Lay Summaries Archive

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Early View Lay Summaries

 

Plant communication in a widespread goldenrod: keeping herbivores on the move

André Kessler and Kimberly Morrell Photograph provided by authors.

Plants can exchange information with neighbouring plants and a complex network of herbivores, predators and parasitoids. The language that plants use for such information transfer is, to a great extent, chemical - released into the rhizosphere (the soil immediately surrounding the roots) or into the air surrounding the plant. Chemical communication between neighbouring plants through airborne volatile organic compounds (VOCs) has to date been documented in over 35 plant species spanning 16 families; however, the underlying mechanisms through which it shapes plants’ ecological interactions remain less clear. Using a combination of field/laboratory bioassays and airborne volatile and leaf chemical analyses in tall goldenrod (Solidago altissima), we tested the hypothesis that plant-to-plant communication affects the performance, feeding and movement behaviour of herbivores by changing plants’ chemical phenotypes. We found that plant communication accelerates herbivore movement between host plants while simultaneously reducing herbivory. This suggests that plant communication can limit herbivore loads by keeping herbivores on the move between host plants.

We also demonstrate that volatile chemicals emitted from herbivore-attacked plants are sufficient to explain metabolic responses in, and ecological consequences for, the exposed neighbour plant. Thus, volatile organic compounds emitted by stressed plants provide neighbouring plants with specific information about herbivores in the vicinity. The attacking herbivores, in turn, respond similarly to directly damaged plants and plants exposed to VOCs from damaged neighbours, as if they were of equivalently poor quality.

This study suggests that by enlarging the spatial scale at which induced resistance affects the distribution of plant chemical phenotypes in plant populations, VOC-mediated plant communication alters the movement behaviour and performance of herbivores.

Image caption: Photograph provided by authors.
Read the article in full here.

 

Plant genotype identity and intra-specific diversity trump soil nutrient availability to shape old-field structure and function

Lara Souza, Katharine L. Stuble and Aimeé T. ClassenPhoto provided by authors.

Biodiversity, often measured as the number of species in a community, can promote services within ecosystems such as sequestration of carbon from the atmosphere. Biodiversity within a species, or specifically the number of genotypes within a species, may be just as important in promoting ecosystem services, especially when considering a common species. Solidago altissima, also known as tall goldenrod, is a commonly found plant in abandoned agricultural fields ranging from Florida into northern Canada. Tall goldenrod can make up almost half of the total productivity of old fields and is associated with a large number of insects including herbivores, predators and pollinators. To explore the role of biodiversity within tall goldenrod, and how the environment may influence biodiversity effects on ecosystem services, we established a field experiment where Solidago genotypes occurred in monocultures vs. mixtures under ambient vs. added soil nutrients, to mimic the variability of resources found across space and time. Our findings indicate that plant genetic variation, and to some extent plant genotypic diversity, strongly influence carbon sequestration in old fields, and such effects took place regardless of soil nutrient availability.

Image caption: Photo provided by authors.
Read the article in full here.

 

Fire ant queen choices are behind fire ant success

Walter Tschinkel and Joshua KingThe experimental plots in the Apalachicola National Forest in Florida. Several tilled plots and shade covers are apparent.

One of the basic questions of ecology is how and why particular sets of species (called communities) live together; to what degree does the physical nature of the habitat limit the species present, and to what degree do species' interactions? Solid answers to such questions cannot be derived from the existing species co-occurrence, but must be derived from experiments.

The fire ant, Solenopsis invicta, is an exotic, invasive ant found primarily in human-disturbed habitats, and is absent from most undisturbed, native habitat such as the coastal plains pine forests of northern Florida. However, fire ants quickly colonize soil and vegetation disturbances in these forests and thrive until these revert in time to a less disturbed condition. We previously showed that soil disturbance reduces the native ant populations. Newly-mated, dispersing fire ant queens locate these disturbances while in flight and settle in them preferentially to try to establish new colonies. The question is, do they know what they are doing? Does settling in such sites improve their chances of success?

We set up experimental plots in a Florida pine forest with all combinations of soil tilling, shading and reduction of the native ant community (using poison baits). We then planted newly-mated fire ant queens, incipient colonies and small colonies in these plots and followed their survival. Survival of newly-mated queens and incipient colonies was extremely low, but those that did survive were exclusively in plots in which native ants had been reduced and/or the soil disturbed. Planted small colonies fared much better: in plots with reduced native ants, 21 of the 108 planted colonies (19%) were still alive 15 months later, while in plots with an intact native ant population, less than 2% of the 108 colonies survived.

By choosing to land in disturbed habitat with its reduced native ant population, newly mated fire ants queens increase their chances of successful colony establishment. This ant community is thus assembled primarily by queen habitat choice and secondarily by competition. Queens do know what they are doing.

Image caption: The experimental plots in the Apalachicola National Forest in Florida. Several tilled plots and shade covers are apparent.
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Tree height, not fruit shape or weight, predicts how far wind dispersed seeds fly

Carol K. Augspurger, Susan E. Franson, and Katherine C. Cushman A representative dispersal unit of each of 12 wind-dispersed study species in Panama.  The results show that tree height and number of dispersal units, and not how fast the dispersal unit falls, explain the pattern of seeds distributed around the parent tree.Image provided by authors.

Seeds that disperse further from their parent tree often have a better chance of survival. Seed dispersal may send a parent’s offspring to areas with more light, and therefore improved growth. Also, offspring may arrive in areas of lower seed density and away from the parent tree where fungi and herbivores are less likely to attack them. However, how a parent controls where its offspring are dispersed is unclear. This study provides insights into factors critical in predicting the pattern of seeds that fall around a parent tree. This pattern is important because dispersal determines how many of a parent’s offspring survive.

Here, we studied wind-dispersal by 12 Panamanian tree species. Our results showed that dispersal units with a higher weight to area ratio fell faster in still air. However, this speed of fall did not predict dispersal distance when many dispersal units were released from a 40 m tower in the forest. Likewise, these traits did not explain how far a seed landed after natural dispersal from the parent tree.

The pattern of seeds around parent trees of the 12 species differed greatly. We found that taller trees had greater average and maximum seed dispersal distances. Trees dispersing a greater number of seeds also had a greater average dispersal distance. In contrast, a seed’s speed of fall in still air, which is related to how long it is exposed to winds, was not important. Generally, the tree variables predicted dispersal distance well, but unaccounted factors about the dispersal unit or the parent tree, or, more likely, variation in wind speeds that seeds experienced after release, were also important.

Therefore, tree traits explained dispersal distances of these wind-dispersed species, particularly over long distances where offspring survival is enhanced. Apparently, a taller tree exposes its seeds to stronger winds, particularly updrafts after they are released, and carries them to farther distances and lower densities, and perhaps to higher light where some offspring may survive. Future studies should focus on wind strengths needed to release the seeds from the tree, as well as wind patterns after release, to improve our understanding of dispersal.

Image caption: A representative dispersal unit of each of 12 wind-dispersed study species in Panama. The results show that tree height and number of dispersal units, and not how fast the dispersal unit falls, explain the pattern of seeds distributed around the parent tree. Image provided by authors.
Read the article in full here.

 

Intraspecific trait variation across multiple scales: the leaf economics spectrum in coffee

Adam Martin, Bruno Rapidel, Olivier Roupsard, Karel Van den Meersche, Elias de Melo Virginio Filho, Mirna Barrios and Marney Isaac Photograph provided by authors.

Ecologists are interested in knowing how changes in biodiversity affect ecosystems. Specifically, they are often interested in understanding how biodiversity losses reduce the “services” that ecosystems provide. In agricultural systems for example, we are interested in knowing how reduced diversity affects crop yield, pest outbreaks, or crop responses to climate change. For a long time, ecologists have measured biodiversity simply as the number of species in an ecosystem. But more recently they are interested in “functional diversity”: in other words, the range of leaf, root and stem types that are present in an ecosystem.

Generally, functional diversity is a better predictor of ecosystem services than simply the number of species, so it has become important to know which are the most ecologically important functional traits in plants. Leaf functional traits – notably, photosynthetic rates, the amount of nitrogen in a leaf, and leaf mass per area – get the most attention. One main way ecologists have come to know these traits are ecologically important is by examining how they relate to one another. Looking at the leaves of hundreds of species, they have uncovered general trends in plants globally: as leaf nitrogen goes up, photosynthesis goes up, and leaf mass per area goes down.

While we know this happens across plant species in natural ecosystems (or “wild” plants), we are still unsure i) if these relationships occur when we look across different individuals of the same species, or ii) if these relationships in wild plants also occur in crops, which have been domesticated over many years.

We looked at these questions in coffee, one of the world’s most common (and well-loved) crops. We found that the same leaf traits that are ecologically important in wild plants are also ecologically important in coffee. Specifically, we found that across nearly 400 leaves from 100 coffee plants, as leaf nitrogen goes up, photosynthesis goes up, and leaf mass per area goes down. But in coffee, these relationships are not the same as in wild plants, possibly because coffee has been bred to have a lot of caffeine, much of which may be in leaves.

Image caption: Photograph provided by authors.
Read the article in full here.

 

Climate and tree vigour control the timing of wood formation in deciduous oaks

Gonzalo Pérez-de-Lis, José Miguel Olano, Vicente Rozas, Sergio Rossi, Rosa Ana Vázquez-Ruiz and Ignacio García-GonzálezTransverse section of wood from pedunculate oak (Quercus robur). Dividing cells in the cambial zone (centre) give rise to new phloem (top) and xylem (bottom) tissues.

Trees produce new wood during their whole lifespan. Tissue known as ‘vascular cambium’ generates a new tree ring that is disposed over the existing wood tissues every year. To sustain the machinery of growth, trees need to invest large amounts of carbohydrates produced in the leaves via photosynthesis. Trees adjust how they function in different climates by shifting the timing of growth (i.e. phenology), although this can influence the capability of trees to produce wood. Understanding how phenology affects wood production is of special relevance in the context of climate warming, which is modifying phenological patterns in terrestrial plants.

We monitored wood and leaf formation, and the content of non-structural carbohydrates (NSC), in the stems of two deciduous species, pedunculate oak (Quercus robur) and Pyrenean oak (Quercus pyrenaica), in three sites located along a humidity gradient in northwestern Spain. Although Pyrenean oak is better adapted to drought than pedunculate oak, both species coexist along the transition between the temperate and Mediterranean regions. We also assessed the impact of the number of cambial cells in winter (higher in more vigorous trees) on wood production and phenology during the following growing season.

Pedunculate oak was more productive and had a longer growing season than Pyrenean oak, but both species showed comparable seasonal changes in growth activity and carbon reserves. We show that, under warm and dry conditions, deciduous oaks reduce or even stop growth in summer, but extend the growing season in spring and autumn. Stem NSC dropped in spring simultaneously with the onset of growth, and recovered in summer after the formation of new leaves. Trees with more cambial cells in winter had a longer growing season and produced more wood. This result indicates that tree vigour acts as a predisposing factor for growth, modulating carbon demands throughout the year.

Image caption: Transverse section of wood from pedunculate oak (Quercus robur). Dividing cells in the cambial zone (centre) give rise to new phloem (top) and xylem (bottom) tissues.
Read the article in full here.

 

Integrating intraspecific variation in community ecology unifies theories on bodysize shifts along climatic gradients

Alice Classen, Ingolf Steffan-Dewenter, William J. Kindeketa, Marcell K. PetersImage provided by the authors.

Species traits, like the size and shape of organisms, change along broad-scale climatic gradients. Probably the most famous biogeographical pattern in this context is Bergmann’s rule, which says that species tend to get larger in cooler environments. This has been explained by the fact that species with larger body sizes are energetically favoured because they lose less heat, in relative terms, due to a reduced surface-to-volume ratio. An alternative hypothesis is that energy availability effectively limits the maximum size of organisms. Absolute energy requirements of larger organisms are higher than those of smaller organisms, i.e. they need more energy and space to maintain critical population sizes and are predicted to face higher extinction risks in energy-limited environments. Thus, the predictions concerning body size distributions are contradictory.

Tropical mountains provide excellent conditions to study the patterns and drivers of species traits, as here potential drivers like temperature, area and resource availability change rapidly, making ecological studies feasible. In this study we analysed the body size distributions of wild bees on the highest free-standing mountain in the world, Mount Kilimanjaro (Tanzania). As we assumed that different drivers may operate at different levels of biological organization we studied trends in body size at both the community and species level.

We show that Bergmann´s rule and energy-based predictions are both evident in bee communities along the elevational gradient of Mt. Kilimanjaro. While individuals within species became on average larger with increasing elevation, communities in cooler habitats were increasingly dominated by smaller species. Thus, whether evidence for one or the other hypothesis is found depends on the level of biological organization. We conclude that the integration of intraspecific variation into community ecology can unify conflicting theories on body size shifts along temperature gradients.

Image caption: Image provided by the authors.
Read the article in full here.

 

Wood anatomy reflects different ecological strategies in tropical rainforest lifeforms

Deborah M.G. Apgaua, David Y.P. Tng, Lucas A. Cernusak, Alexander W. Cheesman, Rubens M. Santos, Will J. Edwards and Susan G.W. LauranceAnatomy of a rainforest liana Strychnos minor showing large and largely solitary vessels. Image provided by the authors.

Tropical rainforests harbour a large portion of the world’s plant diversity, yet many scientists fear these communities are at risk from increasing drought events. In order to understand how forests with thousands of species will respond to droughts, we explored how plants that live in different parts of the forest differ in form and function.

We studied 90 plant species in a lowland rainforest in northeast Australia that differed in their habitat preferences, ranging from the dark understorey to the tops of trees. These species formed six ecological groups: mature-phase trees, understorey trees, pioneer trees, understorey shrubs, pioneer shrubs and vines. We sampled wood from these species to collect data on anatomical features related to water transport, such as vessel sizes, frequency and distribution. We also collected leaves from each species to quantify leaf intrinsic water use efficiency through carbon isotope ratios, a measure of how much carbon could be taken up by photosynthesis for a given amount of water lost to transpiration.

Across our study species, we found a spectrum of different wood characteristics. Large climbing plants called lianas, for instance, had low wood densities and exhibited large solitary vessels, indicating an ecological strategy that maximizes water transport at the expense of mechanical support. At the other end of the spectrum, understorey shrubs and trees had high wood densities and numerous small vessels, possibly reflecting a higher investment in structural support, and the reduced need for high water transport. Vessel size was also a strong predictor of water use efficiency across our 90 study species, indicating that plants with larger vessels, and thus a higher potential for water transport, are able to fix more carbon per unit of water transpired. We therefore provide a framework for understanding plant performance through wood functional anatomy and a plant functional group approach.

Image caption: Anatomy of a rainforest liana Strychnos minor showing large and largely solitary vessels. Image provided by the authors.
Read the article in full here.

 

Mosses in Californian grasslands in a changing environment

Risto Virtanen, Anu Eskelinen and Susan Harrison A view over the experimental site at McLaughlin Nature Reserve (Inner Coastal Ranges, California) with harsh serpentine (background) and non-serpentine grassland (foreground). The green grassland patches in the middle of harsh serpentine are created by simulated eutrophication and increased rainfall. In these grasslands, typical bryophytes include Didymodon vinealis (left insert) and Fissidens sublimbatus (right insert). Photos by Anu Eskelinen and Risto Virtanen.

Bryophytes (mosses) are small spore-producing plants that occur in most global ecosystems. Even where they are relatively scarce, such as in semiarid grasslands, bryophytes still may play important roles in various processes such as nutrient cycling, surface water dynamics or vascular plant regeneration. Human impacts such as projected climate shifts and nutrient deposition are likely to change both the abundances and the ecological role of bryophytes.

We simulated two environmental changes, increased springtime rainfall and increased nutrient availability, in a semiarid grassland in California. Both of these changes are already known to make grassland plant communities more productive and more strongly dominated by tall vascular plant species such as exotic annual grasses. In turn, this increase in productivity has been shown to suppress the abundance and diversity of smaller vascular plants, many of which are native annual forbs (“wildflowers”). We asked whether bryophytes would show this same competitive suppression of abundance and diversity under enhanced rainfall and nutrients.

As predicted, both bryophytes and small vascular plants declined under our rainfall and nutrient addition treatment as biomass and tall plant dominance increased. In contrast, adding water alone benefited bryophytes but not small vascular plants, while adding nutrients alone benefited small vascular plants but not bryophytes. In general, our results support the idea that environmental changes that enhance grassland productivity and dominance of tall vascular plants are likely to harm grassland diversity, including bryophytes as well as small vascular plants.

Image caption: A view over the experimental site at McLaughlin Nature Reserve (Inner Coastal Ranges, California) with harsh serpentine (background) and non-serpentine grassland (foreground). The green grassland patches in the middle of harsh serpentine are created by simulated eutrophication and increased rainfall. In these grasslands, typical bryophytes include Didymodon vinealis (left insert) and Fissidens sublimbatus (right insert). Photos by Anu Eskelinen and Risto Virtanen.
Read the article in full here.

 

How will climate change affect predatory invasive species?

Brian S Cheng, Lisa M Komoroske and Edwin D GrosA predatory Atlantic oyster drill rests upon an Olympia oyster. In many parts of the world, oyster drills have been accidentally introduced and may pose a problem for native oysters. These negative effects may intensify with climate change. Oyster drill egg capsules can also be seen on the right side of the photo. Photo credit: Brian Cheng.

The spread of invasive species has resulted in tremendous economic impacts and losses to biodiversity across the planet. There is concern that climate change may worsen the impacts of invaders, partly because many of these species appear to be more tolerant of changing environmental conditions than their native counterparts. However, most of our knowledge in this area is from alien species that are taxonomically related to or that compete with natives. Invasive predators are among the most disruptive non-native species, yet we know almost nothing of how these animals may respond to climate change. To address this, we examined the physiology of two invasive predators (oyster drills – predatory sea snails) and their native prey (oysters) to understand how these species may respond to warming and extreme flood events. We found that these predators were generally less tolerant of extreme climate change conditions as compared to their prey. However, when animals were exposed to conditions representing near-term warming, predator performance and foraging on prey oysters increased greatly. These observations are supported by previous field measurements that indicate intense predation on oysters at the warmest sites. In addition, both invasive predators exhibited different temperatures of peak performance, suggesting that there is a broad temperature range over which predators will consume prey oysters.

Although extreme events appear to favor prey oysters, near-term warming trends may ultimately reduce their abundance in nature. This is a concern, because wild oysters have experienced declines of up to 88% over the last century due to overfishing and habitat degradation. In response, there are active efforts to conserve and restore oyster populations in many parts of the world. Our work suggests that climate change and the invasion of non-native species may severely hamper the recovery of oysters. Future efforts to assist native oysters should consider attempting to eradicate invasive predators that may benefit from climate change.

Image caption: A predatory Atlantic oyster drill rests upon an Olympia oyster. In many parts of the world, oyster drills have been accidentally introduced and may pose a problem for native oysters. These negative effects may intensify with climate change. Oyster drill egg capsules can also be seen on the right side of the photo. Photo credit: Brian Cheng.
Read the article in full here.

 

Does differential processing of coral and algal exudates by reef sponges influence dissolved organic matter cycling via the “sponge loop”?

Laura Rix, Dick van Oevelen, Ulrick Struck, Fuad Al-Horani, Christian Wild and Malik NaumannImage provided by authors.

The efficient recycling of nutrients on coral reefs contributes to the characteristic high productivity of these diverse underwater ecosystems. The main primary producers on coral reefs, corals and algae, release large quantities of their excess products from photosynthesis as energy-rich dissolved organic matter (DOM). This DOM represents the largest source of organic matter produced on coral reefs, but most reef organisms that rely on organic matter as a source of energy cannot directly utilize DOM as a food source. Sponges are not only able to consume DOM, but they also transform and release a fraction of the DOM they assimilate as particulate detritus, which can then be used as a food source by many other reef organisms. This sponge-mediated DOM recycling pathway has been termed the “sponge loop” and plays a key role in transferring the energy and nutrients in DOM to higher trophic levels on coral reefs. Interestingly, the DOM released by corals and algae differs in composition and nutritional quality, but the influence of these different DOM sources on recycling by sponges has not been investigated.

We used incubation experiments to compare the processing of coral- and algal-derived DOM by three coral reef sponge species from the Red Sea: Chondrilla sacciformis, Hemimycale arabica, and Mycale fistulifera. We found that the sponges took up and assimilated both coral- and algal-derived DOM into their tissue biomass, but that uptake rates were significantly higher for algal-derived DOM. A substantial fraction (15–49%) of the coral- and algal-derived DOM assimilated by the sponges was subsequently converted into and released as particulate detritus. However, algal-derived DOM was released as detritus at a higher rate. These findings suggest that sponges process and recycle algal-DOM more rapidly than coral-derived DOM. As coral reefs are increasingly threatened by anthropogenic impacts, many corals reefs are undergoing community shifts from coral to algal dominance. By demonstrating that the DOM produced by algae enhances DOM recycling via the sponge loop, our findings have potential consequences for both nutrient cycling and the transfer of energy through food webs on coral reefs.

Image caption: Image provided by authors.
Read the article in full here.

 

Moose in disturbed forests: impacts on plant regeneration, litter decomposition and soil composition

Nichola Ellis and Shawn LerouxImage provided by authors.

Herbivores, such as moose, can play an important role in ecosystems. By selectively feeding on certain plant species, herbivores can reduce the growth of their preferred plants and promote growth in those plant species they avoid. Herbivores usually consume plants that are relatively high in nitrogen and phosphorus and avoid plants that are relatively high in carbon and non-palatable toxins. Most of the plant material not consumed by herbivores dies and becomes litter which then decomposes in the soil. Depending on feeding preferences, herbivores can dramatically change the concentrations of carbon, nitrogen and phosphorus in the soil. This could influence plant growth, and the insects, birds and other animals that depend on plants.

Evidence from studies in boreal forests in North American show that moose, via their feeding activities, can change plant communities, decrease the amount of carbon, nitrogen, and phosphorus in soils and decrease the time it takes for litter to decompose. We tested the influence of moose and abiotic conditions, such as climate, on plant communities and soils in Newfoundland, Canada, a temperate marine island with different climatic and environmental history from that in other studies.

We used 10 large fenced areas to exclude moose and found that after 15-20 years of moose absence, both preferred and non-preferred plants were able to grow taller, and produce more litter compared to areas where moose were feeding. However, concentrations of carbon, nitrogen, and phosphorus in soils and litter decomposition time were not impacted by moose, while soil depth and soil pH were higher and lower respectively. Our results suggest that, in Newfoundland, environmental conditions such as moisture and disturbance history may have a greater impact on soil quality and litter decomposition than moose presence. We show that future studies of herbivore impacts on forests should consider the importance of environmental conditions. In Newfoundland, Parks Canada should continue to monitor moose populations and forests to see if the effect of moose on forest ecosystems changes over time.

Image caption: Image provided by authors.
Read the article in full here.

 

The outcome of competition between two parasitoid species is influenced by a facultative symbiont of their aphid host

Ailsa H.C. McLean & H. Charles J. GodfrayAphelinus abdominalis parasitizing Acyrthosiphon pisum. Photo by Jan Hrček.

Many insects have close and ongoing relationships with symbiotic bacteria, which can provide a number of different benefits, including defence against natural enemies. In this study, we asked whether this protection can affect how different natural enemies interact with one another; specifically, can symbiont-mediated protection alter the outcome of competition between natural enemies?

We studied aphids which carry a symbiotic bacterium that can provide protection against parasitoid wasps. The wasps lay their eggs inside aphids, and the developing wasp larva eventually kills the aphid, but not until the very end of its development. The symbiotic bacteria can act to kill the wasp at an early stage, but the symbionts are not equally effective against all wasp species. We used a symbiont strain which is known to provide strong resistance against one species, Aphelinus abdominalis, but much weaker resistance against a second species, Aphidius ervi. We asked how this asymmetric protection affects the outcome of competition between these two different wasp species when they lay eggs in the same aphid. In these interactions, only one wasp can develop successfully.

We allowed a female of first one wasp species, then a female of the other wasp species, to lay one egg each in a single aphid and compared the outcome for aphids with and without the symbiont. We asked which wasp species successfully developed, or did the aphid survive? We found that, in symbiont-free aphids, the first wasp to oviposit gained an advantage. However, A. abdominalis never survived in the presence of the symbiont. This allowed A. ervi, which would normally have been the inferior competitor, to develop successfully in aphids with the symbiont, even when it parasitized the aphid second. Our results show that protective symbionts do not only affect the interaction between the host and a natural enemy, but also the outcome of competition at the next trophic level.

Image caption: Aphelinus abdominalis parasitizing Acyrthosiphon pisum. Photo by Jan Hrček.
Read the article in full here.

 

Competition shaping the phytoplankton communities, judged from the functional properties of the species

Riina Klais, Veera Norros, Sirpa Lehtinen, Timo Tamminen and Kalle OlliMorphological diversity of phytoplankton, from single cells to different colonies and chains. Photo credit: Dr. Richard Kirby.

Understanding the rules of species coexistence is central for ecological research. Phytoplankton – free-living phototrophic protists and cyanobacteria (the bluegreens) – are known to be controlled by temperature, salinity, light, and nutrients. Species’ environmental preferences define the biogeography and seasonality of phytoplankton functional groups (the most well known being diatoms, dinoflagellates and blue-greens). This knowledge is already used to inform global plankton models. Much less is known about the role of biotic interactions – especially competition – between phytoplankton species in the assembly of natural communities.

We analysed a large coastal phytoplankton dataset, consisting of nearly 8000 samples, collected from the Baltic Sea over the last 30 years, and covering the seasonal cycle and wide salinity and temperature gradients. We first estimated the preferred habitat of every species. From that information, we constructed the simulated communities – as they should be, if only the environment determines community composition. These simulated communities were then compared against the actually observed communities.

We investigated whether the species in the observed community were functionally more or less similar to each other than the simulation predicted. The similarity was judged from characteristics such as body size, ability to fix atmospheric nitrogen, whether they are both auto- and heterotrophic at the same time, whether they swim around, make colonies or chains to change the body shape and avoid predators, and the composition of accessory pigments that phytoplankton use to harvest all the different wavelengths of light that penetrate the water.

When comparing the simulated and observed communities, we found that one in every four communities was notably shaped by competition, because species in it were either too similar, or too dissimilar to each other for their coexistence to be explained only by the environment.

Image caption: Morphological diversity of phytoplankton, from single cells to different colonies and chains. Photo credit: Dr. Richard Kirby.
Read the article in full here.

 

Which are the drivers of animal personality: hormone levels or metabolic rates?

Benedikt Holtmann, Malgorzata Lagisz and Shinichi NakagawaColour-ringed dunnock (Prunella modularis) from the Dunedin Botanic Garden, New Zealand. Photo credit Stefanie Grosser.

Animals of the same population often show individual variation in their behaviours, which are consistent over time (i.e. repeatable). For example, some individuals are consistently more active, more explorative or more aggressive than others. While these repeatable behavioural differences, referred to as animal personality, have been described in various species, we still know very little about their underlying mechanisms and how personality differences are maintained. Recent studies in the field of animal personality have proposed that consistent individual differences in hormone levels and/or metabolic rates may be responsible for mediating consistent behavioural differences. Thus, here we investigate the relationship between behavioural and the two proposed physiological traits by testing the hypothesis that physiological traits (hormones vs. metabolism) that mediate consistent individual differences in behaviour exhibit similar or higher time-consistency (i.e. repeatability) compared to behavioural traits.

We systematically reviewed published (and unpublished) data from bird species on the repeatability of hormone levels, metabolic rates and behavioural traits, combining results from all relevant articles. Our analyses revealed that both metabolic rates and behavioural traits were highly repeatable and that repeatability estimates of both traits were of similar magnitude. Conversely, the repeatability of hormone levels was three times lower, suggesting that individual hormone levels are more variable over time. These results indicate that individual differences in metabolic rates, rather than hormone levels, are likely a key mechanism involved in generating consistent individual differences in behaviour.

Moreover, additional analyses revealed three more notable findings. First, repeatability estimates of hormone levels and behavioural traits decrease with increasing interval time between two consecutive measurements. Second, males and females differ in repeatability for behavioural traits. And third, hormone level measurements, taken within a few minutes after the capture of an individual (baseline levels) show higher variation than hormone levels taken at least 30 minutes after capture (stress-induced levels).

By conducting meta-analyses, we show that metabolic rates are likely one of the mechanisms underlying consistent individual differences in behaviour. Future studies are now needed to investigate the relationship between metabolic rates and personality traits in more detail.

 

Aphid-generated indirect interaction network

Yoshino Ando, Shunsuke Utsumi and Takayuki OhgushiFigure showing how aphid created an interaction network through ant-mediated and plant-mediated indirect effects.

A wide variety of herbivorous insects may share a host plant. Since the strength and direction of an interaction between two species can be indirectly altered by a third species, multiple insect herbivores on plants can interact directly and indirectly with each other.

Herbivory can induce morphological and/or chemical changes in plants, thereby affecting interactions with subsequent insect herbivores, called a plant-mediated indirect effect. Although past studies have focused on interactions between co-occurring species, plant-mediated indirect effects can affect plant-associated arthropod communities by connecting species that are separated in time and space. However, little is known about how and to what extent multiple direct/indirect interactions can create an interaction network through plant-mediated indirect effects.

We focused on the potential role of an aphid in creating an interaction network on tall goldenrods, and used an aphid exclusion experiment to examine how the aphid affects the interaction network through aphid-generated indirect effects and its consequence for plant reproductive success .

The aphid played a critical role as a network creator in determining the interaction network. The aphid indirectly decreased co-occurring insects through their removal by ants (an ant-mediated indirect effect). Also, late in the season when the aphid was no longer present, it still indirectly decreased scale insects but increased grasshoppers through aphid-induced leaf regrowth. As a result, aphid-induced leaf regrowth greatly contributed to an increase in the interaction diversity and complexity by connecting co-occurring and temporally-separated herbivores. Moreover, the aphid-generated interaction network could improve the reproductive success of tall goldenrods by increasing seed production.

Image caption: Figure showing how aphid created an interaction network through ant-mediated and plant-mediated indirect effects.
Read the article in full here.

 

Insects adapt in real-time to cold but not hot temperatures

Mads Fristrup Schou, Marie Brandt Mouridsen, Jesper Givskov Sørensen & Volker Loeschcke To measure the cold tolerance of small insects, they are distributed individually to small numbered glass tubes, which are lowered into a fluid with a low freezing point (<10°C). Hereafter, several machines work together to perform a controlled decrease in temperature, while every single fly is monitored through the glass. The temperature at which all movement of a fly stops is noted, and is a measure of the cold tolerance. Photograph credit: Mads F. Schou.

The ability of insects to evolve and adapt to an increased or a decreased temperature is receiving a great deal of attention, as a consequence of current and future climate change. But adaptation through evolutionary change, which typically requires multiple generations, is not the only way organisms can adapt. Organisms have a remarkable ability to adjust important traits during their lifetime, to stay well aligned with the environment at hand. One example among many is the drastic change in fur color of snowshoe hares from brown to white before the arrival of winter. Do insects also have the ability to readily adjust their physiology or morphology? If insects can increase their cold tolerance when winter is coming, and increase their heat tolerance as the temperature increases during summer, this may be a short-cut for dealing with the expected changes in temperature during the next century. In an attempt to answer this question we investigated 13 species of fruit flies, with distributions that are either world-wide or restricted to deserts, the cold northern climate or the tropical climate. Throughout the entire life cycle, the flies were reared at one of several different temperatures spanning their entire tolerable temperature range. We then estimated the ability to adjust their physiology and thereby align their tolerance according to the given temperature. All 13 species had a surprisingly strong ability to readily adjust their cold tolerance as a response to rearing temperature. This ability is without doubt central for their ability to survive in natural habitats. Conversely, all species had very limited ability to increase their heat tolerance when reared in warmer temperatures, and some species even suffered a decrease in heat tolerance, likely because the high temperatures stressed them. In conclusion, heat tolerance is a highly fixed trait which is unlikely to be rapidly adjusted within generations as an adaptive response during a changing climate, at least in comparison to the strong response with respect to cold tolerance.

Image caption: To measure the cold tolerance of small insects, they are distributed individually to small numbered glass tubes, which are lowered into a fluid with a low freezing point (<10°C). Hereafter, several machines work together to perform a controlled decrease in temperature, while every single fly is monitored through the glass. The temperature at which all movement of a fly stops is noted, and is a measure of the cold tolerance. Photograph credit: Mads F. Schou.
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Handbook of protocols for standardized measurement of terrestrial invertebrate functional traits

Marco Moretti, André T.C. Dias, Francesco de Bello, Florian Altermatt, Steven L. Chown, Francisco M. Azcárate, James R. Bell, Bertrand Fournier, Michael Hedde, Joaquín Hortal, Sébastien Ibanez, Erik Öckinger, José Paulo Sousa, Jacintha Ellers and Matty P. BergPhotographs of Isopoda  by Theodoor Heijerman.

Traits are simply species characters that can be measured or observed directly and are commonly a descriptor of a behavioural or morphological adaptation. The first well known observation was made by Charles Darwin who famously described the shape of finch bills and their functional relationship with seed size and form. Beyond shape and form, traits strike at the very heart of how individuals increase their survival and fitness in relation to environmental conditions - Darwin’s theory of natural selection brilliantly illustrated that. Relating traits to functions can ultimately provide a measure of how key ecosystem processes and services, like nutrient cycling and pollination, might be affected if communities were to change. Perhaps not surprisingly, the practical side of trait ecology is little different to how taxonomists collect measurements to describe new species: ecologists collect measurements like body size, life span, eye morphology and these are then mapped using a standardized protocol. Measurements are projected in a ‘trait space’ that displays the range and variability of traits of interest, and in doing so, seemingly unrelated species are linked to identify general principles and emergent ideas. Traits have yet to realize their full potential because the methodology is rarely standardized outside of plant ecology, an issue that we try to resolve in this paper for terrestrial invertebrates. We propose the first handbook of protocols for standardized measurements of 29 terrestrial invertebrate traits known to be sensitive to global stressors and to affect key ecosystem processes and services. As has been the case with plants, standardized functional traits will be used in the future to explain invertebrate community assembly, species diversity patterns, and ecosystem processes and services within and across taxa and trophic levels. Meta-analyses across regions and ecosystems will likely highlight future weaknesses and vulnerabilities in communities, as they have done to some extent with pollination. Importantly, we have left room for new knowledge to be incorporated into the trait protocols, using a standard format within which researchers can further provide methodological input for additional special cases.

Image caption: Photographs of Isopoda by Theodoor Heijerman.
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Special Feature: The Ecology of De-Extinction

Using palaeoecology to determine baseline ecological requirements and interaction networks for de-extinction candidate species

Jamie R. Wood, George L. W. Perry, Janet M. WilmshurstCoprolites, such as this of an extinct New Zealand moa, are a source of detailed information on the habitat and dietary requirements, microbiota and parasite communities of extinct species. Photo by J. R. Wood.

One of the main drivers for research into de-extinction (or reviving extinct species) is the potential for returning lost processes and function to modern-day ecosystems. For example, some extinct animals may have been the sole pollinators or seed dispersers for particular plant species, which have now declined themselves as a result of the extinction. Other extinct animals may have played key roles in nutrient deposition, and their extinction may have had major flow-on effects for nutrient cycles. Restoring such species is seen as likely to have beneficial results for ecosystems.

However, this viewpoint focusses mainly on what de-extinction candidates can do for ecosystems. We must also understand and provide the ecological requirements of candidate species, as this will play a key role in determining the success of a de-extinction. Aspects of these include: (i) habitat requirements; (ii) dietary requirements; (iii) microbiota communities; and (iv) parasite communities. Information on these can be challenging to obtain for extinct species, but here we review how different palaeoecological sample types and analytical techniques can be used to gain insights into such requirements. Although palaeoecological data have an important role in guiding and informing the selection of suitable de-extinction candidates, they can only ever provide an incomplete picture, and therefore must complement, rather than replace, observational or experimental data on the resurrected organisms themselves.

Image caption: Coprolites, such as this of an extinct New Zealand moa, are a source of detailed information on the habitat and dietary requirements, microbiota and parasite communities of extinct species. Photo by J. R. Wood.
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Physiological maturity at a critical life-history transition and flight ability at fledging

Allison Cornell, Kate F. Gibson and Tony D WilliamsA fledgling European starling (Sturnus vuglaris) attempts to take off in flight, photo by A. Cornell.

It’s a dangerous world out there for young birds leaving the nest. When songbirds fledge, they make a permanent transition from the sedentary lifestyle of a nestling to a highly active, free-flying fledgling. Outside the nest they have to look for food, escape from predators, and navigate in their habitat. Reported rates of survival show that nearly half of chicks that make this transition die almost immediately, largely due to predators who mark them as easy prey. It’s no surprise that predators choose to go after these juvenile birds; they’re relatively slow to take off, and have poor flight ability.

We investigated the maturity of fledglings on the day they leave the nest, to measure just how developed these young birds are. Consistent with other studies, we found that the values of somatic traits, such as body size and wing length, were smaller than adults. However, when we measured physiological traits that indicate the body’s ability to transport oxygen, we found more than just low trait values. Our fledglings were highly variable in these traits, indicating that this might be a good way to measure the quality of individuals. When we measured the birds’ flight ability, we found that physiological traits were helpful as predictors of take-off angle and energy produced during flight.

When scientists typically study fledglings, only measurements of body size are taken. Our results show that measuring physiological traits might help us distinguish between low and high quality fledglings, because these traits have high individual variation and help predict flight ability. The physiological traits we measured are relatively easy to obtain, and recording these values could greatly impact the way we understand fledglings. If physiological traits are the mechanism driving fledgling flight ability, then for a juvenile bird, physiological maturity could mean the difference between life and death.

Image caption: A fledgling European starling (Sturnus vuglaris) attempts to take off in flight, photo by A. Cornell.
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Review

Does biomass-growth increase in the largest trees? Flaws, fallacies and alternative analyses.

Douglas Sheil, Chris Eastaugh, Mart Vlam, Pieter Zuidema, Peter Groenendijk, Peter van der Sleen, Alex Jay and Jerome VanclayImage provided by authors.

Trees play a major role in the global carbon cycle and our understanding of tree growth informs forest science and management. Yet the characteristic growth pattern of most tree species remains unknown. Until recently most researchers thought that biomass-growth declined at large stem sizes. But recent studies claim to show that biomass-growth increases throughout a tree’s life with no ultimate decline both in forests and in open-grown competition-free environments. Such contrasting views merit careful assessment. Here we examine how methodological issues can influence the detection and interpretation of biomass-growth trends.

Growth studies of large trees pose various challenges. These challenges range from finding enough of such trees (they typically occur at low densities) to measuring them in an accurate and consistent manner (see figure). Correcting stem measurement errors can itself cause biases that increase perceived biomass-growth with tree size. To estimate biomass change from tree measurements requires the size-biomass relationship to be well characterised (calibrated) but for most species and for large stems in general, these relationships remain unknown. Using general species-averaged size-biomass relationships leads to large uncertainties regarding biomass and biomass-growth at large sizes in each species. A problem arises when growth patterns within and among stems are confused (these patterns can be distinct as they reflect distinct ecological processes).

To explore and illustrate some of our concerns we use growth-rings to examine the lifetime growth of 14 tropical tree species. Our examination of estimated biomass-growth in 706 stems indicates similar numbers of positive and negative trends with most trees having relatively flat growth (i.e., without marked trends) over extended periods. Nonetheless, when we compare stems all but one of our 14 species indicate higher biomass-growth in the larger stems. Individual stems and patterns across stems thus lead to contrasting conclusions: any confusion of these would constitute a so called “Ecological Fallacy”.

We note that recent studies concluding that biomass-growth increases as stems grow larger do not in fact examine patterns in individual stems but compare variation in growth among stems. Patterns among stems themselves remain uncertain too, due to errors and possible artefacts. We describe how these problems can be avoided or reduced so as to provide reliable results and conclusions.

Image caption: Image provided by authors.
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Plants direct the dispersal of their seeds towards suitable sites

Merel B. Soons, G. Arjen de Groot , M. Teresa Cuesta Ramirez, Rob G. A. Fraaije, Jos T.A. Verhoeven & Monique de JagerImage provided by authors.

Plants cannot move to find new places to live in – instead, they produce seeds that disperse to sites away from the parent plant. Seed dispersal usually involves the transportation of the seeds by animals, water or wind. Animals may purposely or accidentally pick up seeds and deposit them at another site when they are moving. Depending on the behaviour of the animal, this mode of transportation may be very efficient for plants. For example, the seeds of wetland plants may be ingested by ducks in one pond and excreted after a couple of hours in the next pond visited by the bird. In this way, seeds are transported to new sites that are suitable for the plant species to grow in. Such efficient transportation of seeds towards suitable sites is called ‘directed dispersal’.

Directed dispersal is known mostly for animal-dispersed plant species. However, most plant species are not dispersed by animals but by water or wind. Wouldn’t it be highly efficient for these species as well, if their seeds were dispersed predominantly towards suitable sites? We investigated whether directed dispersal also exists in water-dispersed and wind-dispersed wetland plant species. To this purpose, we studied a range of wetland plant species growing in shorelines, from the permanently inundated, aquatic part to the permanently dry, upland part. We discovered that plants growing under permanently inundated, wet conditions produce large seeds that sink immediately in water. These seeds are transported at the bottom of the pond, stream or ditch by water flows that take them only to other inundated, wet sites. In contrast, plants growing at the waterline produce seeds that float for extensive periods of time until they are eventually washed ashore in… the waterline. In these ways, plants growing in the reach of water use the transportation capacity of water in very different ways to direct the dispersal of their seeds towards suitable sites.

Plants growing on the uplands have seeds that are best dispersed by wind, facilitating their transportation across wet areas to reach dry sites.

Image caption: Image provided by authors.
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Movement ability of an invasive beetle is related to leg length but not body size nor metabolic rate

Pieter A. Arnold, Phillip Cassey, Craig R. White Red flour beetle moving through wheat flour. Schematic of the maze used to assess movement is inset in the top left. Photo: Pieter Arnold.

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Individuals within a species can vary greatly in their ability to move around and disperse within their environment. This variation in movement ability can often be described by physiological, morphological and behavioural traits that are related to dispersal, but the associations among such traits are not always clear-cut or predictable. Previous studies, including work on the invasive cane toad in Australia, have identified that individuals that are larger and have longer legs relative to their body size are able to move farther and faster than smaller or proportionate individuals. In our study, we used an invasive insect species, the red flour beetle, as a model to investigate how movement characteristics related to morphological and physiological traits. Individual beetles were run through a maze that simulated a complex environment, to assess their movement. We identified that movement ability could be described along an axis; individuals that scored positively on this axis moved at higher speed, travelled longer distances, moved continuously, and reached the edge of the maze quicker. Leg length relative to body size was strongly related to movement ability. That is, beetles with relatively long legs had positive movement ability scores, which we hypothesised was because longer legs allow for longer stride length and therefore a greater movement ability. Surprisingly, body size and metabolic rate (energy expenditure) were unrelated to movement ability. This result suggests that dispersal may be more strongly related to the muscles and structures that directly affect locomotion, rather than body size overall or energy-related traits. It will be important for future studies to consider locomotor morphology as a foundation for studying variation in movement and dispersal, especially when investigating the ecology and evolution of traits in invasive or pest species.

Image caption: Red flour beetle moving through wheat flour. Schematic of the maze used to assess movement is inset in the top left. Photo: Pieter Arnold.
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The price of looking sexy: visual ecology of a three level predator-prey system

David Outomuro, Linus Söderquist, Frank Johansson, Anders Ödeen, and Karin NordströmPhoto provided by authors..

Many animals, such as parrots, tropical fish or butterflies, are very colourful. Such colourful displays are favoured in sexual selection as they make the animal stand out, and colour may therefore enhance mating success. However, colour can also be costly, as it makes the animal more conspicuous to both predators and prey. Colourful traits are therefore subject to opposing selection pressures: positive sexual selection by conspecifics (increased mating success) and negative natural selection by predators (higher predation risk) and prey (lowered hunting success). In this paper we studied the conspicuous wing coloration of two species of damselflies, which are predated by birds and prey on small flies. The conspicuous wing coloration is used in colour communication between the sexes and between different species of damselflies. Using electrophysiology, we first determined the colour vision of the damselflies and found that they see well in UV as well as in the human visible range. Second, we measured the wing coloration using spectrophotometry and confirmed that males are more colourful than females. Third, we estimated the predation risk in natural populations by quantifying the predated wings from bird feeding stations, and found that more males than females were consumed. We finally used our data together with previously known colour vision of the bird predator, and the fruit fly prey, to model how visible the wing coloration is in natural environments. We found that males are very conspicuous to bird predators, to other damselflies, and to prey, while females remain predominantly cryptic (i.e. hard to see against the background). This implies that males, but not females, pay a high cost when they use colour to communicate with other damselflies, both in terms of predation risk and visibility to prey. One of our most surprising findings was that male damselflies are unable to discriminate the wing coloration of perching females! We hypothesize that females use this to reduce male harassment, which is very intense in damselflies. Our study demonstrates that by including several levels of interactions in predator-prey systems, we get a more complete understanding of the costs and benefits of being colourful.

Image caption: Photo provided by authors..
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Competing for seed dispersal: evidence for the role of avian seed hoarders in mediating apparent predation among oaks

Mario Pesendorfer and Walter KoenigA western scrub-jay (Aphelocoma californica) searches the branches of a valley oak (Quercus lobata) for acorns at the Hastings Natural History Reservation in Carmel Valley, California. Photo credit: Jenna Kohles.

Species interactions come in many shapes and forms, from predation to mutualisms. Indirect interactions, mediated by a third party, often occur when two or more species share the same generalist predator. When the predators are also seed dispersers, as is the case for many large-seeded trees whose seeds are harvested by seed-hoarding animals, such indirect interactions can shift from seed dispersal mutualism to predation, depending on the relative seed production of the trees that co-occur in a community. Because the shift of mutualistic interactions from one tree species to another results in increased relative predation of the less-dispersed species’ seeds, this indirect effect is termed “apparent predation” – one tree species indirectly preys on the seeds of another.

To investigate the mechanisms underlying apparent predation, we studied the seed predation and dispersal dynamics of valley oaks (Quercus lobata) at Hastings Natural History Reservation in central coastal California, where they mainly co-occur with two other oak species, California blue oak (Q. douglasii) and coast live oak (Q. agrifolia). In the first year of the study, western scrub-jays (Aphelocoma californica), high-quality seed dispersers that scatter seeds across the landscape by hiding them in the ground, attended Q. lobata trees in large numbers to hoard acorns. However, when attending the trees, the jays encountered lots of aggression from another bird species, acorn woodpeckers (Melanerpes formicivorus) that mainly hoard acorns by storing them in so-called granary trees. These low-quality dispersers only help the oaks when they accidentally drop an acorn during transport and thus mainly function as seed predators.

In the second year of the study, Q. lobata and Q. agrifolia acorn crops were similar to the first year, but Q. douglasii crops increased tenfold. With acorns more widely available across the landscape, western scrub-jays only attended Q. lobata trees sparsely, likely to reduce the risk of injury during encounters with the woodpeckers which vigorously defend their preferred valley oaks in year-round territories. The jays have much larger home ranges in the fall and were able to optimise their foraging behaviour by shifting to less-preferred Q. douglasii acorns. As a result, Q. lobata trees experienced a proportional increase in seed predation and almost no seed dispersal from jays. Q. douglasii thus exerted apparent predation on Q. lobata acorns.

Indirect effects mediated by shared seed predators and dispersers may be one of the mechanisms that allows for the co-existence of multiple oak species in forest communities. The variable seed production of each tree species appears to drive seed predation and dispersal dynamics in ways previously not explored. Follow-up studies are necessary to investigate the details of the spatial and temporal variation of such species interactions in order to tease apart the fitness consequences for all the members of the community.

Image caption: A western scrub-jay (Aphelocoma californica) searches the branches of a valley oak (Quercus lobata) for acorns at the Hastings Natural History Reservation in Carmel Valley, California. Photo credit: Jenna Kohles.
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Sexual selection in hybridizing lizards

Hannah E A MacGregor, Geoffrey M While, Jade Barrett, Guillem Pérez i de Lanuza, Pau Carazo, Sozos Michaelides & Tobias Uller A typical Italian male from north-central Italy. Photo by Ben Halliwell.

Populations frequently undergo periods of relative isolation and differentiation that are followed by contact and hybridization (interbreeding). What makes hybridization so striking is the many different ways in which it can act as a catalyst for evolution, such as by accelerating the course of speciation or facilitating adaptation through the exchange of genes. But if members of each population look and behave differently then why does hybridization occur at all? Are some individuals more likely to hybridize than others?

Sexual selection has a reputation for preventing hybridization because females commonly prefer to mate with males of similar genes or traits. But in many animals, including many species of lizard, sexual selection via competition among males is the most important cause of mating patterns within populations. Intuitively, in these species male competition should also influence patterns of hybridization when populations come into contact.

Common wall lizards from north-central Italy have highly exaggerated male sexual traits compared to individuals from Western Europe, having diverged in isolation from one another during the last ice-age. Genetic data from a natural contact zone in northern Italy suggests that hybridization may occur asymmetrically, between Italian males and Western European females. In this study, we used experimental contact zones in outdoor enclosures to investigate the consequences of divergence in male sexual traits (such as body size, testes mass, and colour signals) for male-male competition and patterns of hybridization between Italian and Western European lizards.

During our experiment the Italian males completely dominated the Western European males in aggressive encounters, monopolised high quality territory and the courtship of females, and achieved greater reproductive success. Despite our data suggesting a competitive and reproductive advantage of the Italian males with the most exaggerated traits, these superior Italians were not more likely to hybridize. Instead, hybridization between Italian males and Western European females seems to arise because the Italian males with less exaggerated sexual traits are outcompeted for Italian females but remain competitive relative to the Western European males.

Image caption: A typical Italian male from north-central Italy. Photo by Ben Halliwell.
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The economics of sexual signalling

Thomas M. Houslay, Kirsty F. Houslay, James Rapkin, John Hunt and Luc F. BussièreCrickets.

Sexual selection theory explains the evolution of exaggerated and flamboyant ornaments, displays and mating behaviours in terms of male competition or mating preferences. Such characters are typically costly to produce, but can bring benefits to their bearers: greater mating success for those individuals with the biggest or brightest signals. If an individual produces such signals repeatedly over the course of their adult lifetime, they face ‘trade-offs’ between current and future investment. These trade-offs can create variation in the intensity of signalling at different ages, often interpreted as alternative strategies: ‘live fast, die young’ vs. ‘slow and steady’.

Another possible explanation for this age-related variation is that it is caused by differences in the ability to acquire resources that can be invested in signalling (meaning, for example, that ‘late bloomers’ do not have early investment options). Testing this hypothesis is challenging, not least because measuring both the acquisition and allocation of resources is a difficult task. As an additional complication, an individual’s energetic reserves both affect and are affected by their signalling investment.

Male crickets signal to females using an energetically expensive call, produced by rubbing together their hardened forewings: the more time a male spends calling, the higher his mating success. In this study, we simultaneously manipulated resource acquisition (through diet treatments) and access to females (as a proxy for manipulating sexual signalling) in male decorated crickets (Gryllodes sigillatus). We measured how much time they spent signalling, and how their energy budgets were affected.

Increased diet quality caused increased signalling effort and energy storage, while access to females increased both the likelihood of and time spent signalling. Males with lower resource budgets signalled less, but still suffered energetic losses and reduced lifespan. Our results suggest that energetic constraints, rather than strategic budgeting of resources, led to reduced signalling levels in males with lower acquisition ability. Our findings therefore imply that age-dependent variation in sexual signalling may not represent alternative adaptive strategies. In addition, energetic constraints can help maintain ‘honesty’ in sexual signalling, at least on average: after all, anything spent today cannot be spent tomorrow.

Image caption: Crickets.
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A fundamental problem in finding biomarkers confirmed using feather fault bars in nestling birds

Jelle J. Boonekamp, Rutger Dijkstra, Cor Dijkstra, and Simon VerhulstA female jackdaw (Coloeus monedula) approaching her nest box. Photo by Jelle Boonekamp.

Measuring fitness – essentially the product of survival and reproduction - is central to studies in evolutionary ecology that are aimed at gaining an understanding of natural and sexual selection. But measuring real fitness can be difficult and time-consuming, so fitness biomarkers – traits that predict survival and reproduction – are potentially powerful tools in evolutionary ecology when they can be used as surrogate study end points. For example, most vertebrate species have long reproductive lifespans and therefore valuable time and other resources could be saved by using fitness biomarkers.

Useful fitness biomarkers need to fulfil 2 criteria: (i) they need to be accurate predictors of fitness, and (ii) they need to be sensitive to environmental variation (or experimental manipulation), such that the biomarker successfully links environmental conditions to fitness. However, evolutionary theory predicts that traits that are important for fitness should be well protected (canalized) against the influences of environmental fluctuations, and hence biomarkers that are both accurate fitness predictors and sensitive to environmental conditions may be rare.

Here we tested for this canalization principle using free-living jackdaws. We manipulated the number of siblings in the developmental period to test how strongly developmental conditions affected the number of feather fault bars in tail and wing feathers. Fault bars are deformities on bird feathers associated with developmental stress and can cause feather breakage, thereby impairing flight and insulation. We show fault bars in the tail increased when there were more siblings in the nest, while the number of fault bars in wing feathers was not affected, suggesting tail but not wing fault bar number is sensitive to developmental conditions. In line with evolutionary theory, we found that fault bar number on wings, but not tails, predicted fitness prospects. These results confirm the theory that the development of traits that are important for fitness is strongly canalized.

The canalization phenomenon has implications for the utility of traits as fitness biomarkers, because when traits are good fitness proxies, they are also more likely to be strongly canalised, reducing sensitivity to environmental variation. Intriguingly, there are nevertheless traits that are both sensitive to environmental conditions and predict fitness prospects, and we discuss hypotheses that may explain this paradox.

Image caption: A female jackdaw (Coloeus monedula) approaching her nest box. Photo by Jelle Boonekamp.
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Telomere length and telomerase dynamics in frillneck lizard

Beata Ujvari, Peter A. Biro, Jordan E. Charters, Gregory Brown, Kim Heasman, Christa Beckmann and Thomas MadsenAdult frillneck lizard behind tree.

Much like the plastic tip of shoelaces, telomeres prevent the ends of DNA from fraying during cell divisions. Studies of human cells in culture have shown that telomeres become shorter at every cell division, and when telomeres reach a critically short length (after 50-70 divisions) the cells stop dividing and die. However, many vertebrates produce an enzyme, called telomerase, which replenishes the missing telomere copies. Telomerase not only prevents telomere shortening but is also able to increase the length of critically short telomeres.

In numerous vertebrates, including humans, telomere length (TL) has been shown to decrease with increasing age. Moreover, during recent decades numerous studies have observed an association between TL and organismal survival and/or fitness.

In the present study we therefore investigated how age affected TL and telomerase expression (TE) dynamics in frillneck lizards. We also examined whether TL and TE had any effects on lizard survival. We found that young lizards had short TL, and that TL increased in medium aged lizards but decreased in older cohorts, revealing a curvilinear relationship between TL and lizard age. Higher TE resulted in longer telomeres but in spite of this we did not observe any association between TL dynamics and lizard survival. Instead our results suggest that TL and TE dynamics in frillneck lizards reflect an adaptation to maintain TL above a critical minimum length in order to sustain cellular stability.

Our study has major implications for the role of telomeres in ageing by questioning the significance of TL dynamics as a significant underlying factor in vertebrate survival.

Image caption: Adult frillneck lizard behind tree.
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Endure and call for help: Strategies plants use to deal with a specialised caterpillar

Dani Lucas-Barbosa, Marcel Dicke, Twan Kranenburg, Yavanna Aartsma, Teris van Beek, Martinus Huigens and Joop van LoonCaterpillar of the Large Cabbage White butterfly feeding on flowers of a Black Mustard plant. Photograph credits: Dani Lucas-Barbosa.

Plants have evolved strategies to avoid, resist, and endure damage caused by insect herbivores. Plants may resist herbivore attack by, for instance, changing plant chemistry and producing compounds that are toxic or unpalatable to plant-feeding insects. However, this strategy will not be effective against herbivorous insects that are specialised to withstand the plant’s chemical defences, and will therefore not be deterred from attacking the plant. Thus, plants need to deal differently with specialist herbivores. Plants can, for instance, re-grow leaves to compensate for the tissues lost to plant feeders, invest in flower production and interaction with pollinators, or change odours in order to attract the natural enemies of the herbivores. We studied several strategies that plants can use to deal with herbivores to ensure that they will produce seeds. We investigated the extent to which plants can endure the damage caused by herbivores, and the role of carnivorous insects as a defensive strategy used by plants against their own enemies. In the laboratory, we measured changes in plant basic nutrients (carbon and nitrogen) that are triggered by herbivore attack. In the field, we quantified leaf biomass and seed production in the presence or absence of natural enemies of the herbivores. We also tested whether self-fertilisation increased in mustard plants when exposed to caterpillar damage, and investigated whether caterpillar attack rendered mustard plants more attractive to pollinators than control plants. We found that flowers of mustard plants are rarely visited by insects during the night, and exposure to caterpillars did not influence the rate of self-fertilisation. Mustard plants compensated for caterpillar damage in terms of leaf biomass. However, in the absence of natural enemies of the caterpillars, seed set of these plants was negatively affected by herbivore damage. Once attacked by caterpillars, plants allocated most basic nutrient content to flowers. The investment of plants in flower production or re-growth of leaf tissues per se was not sufficient to sustain seed set of these plants; interactions with the natural enemies of the caterpillars were really essential. We conclude that the natural enemies of the caterpillars play an important role in the plant’s defence strategy.

Image caption: Caterpillar of the Large Cabbage White butterfly feeding on flowers of a Black Mustard plant. Photograph credits: Dani Lucas-Barbosa.
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New insights into the origins of agriculture

Catherine Preece, Alexandra Livarda, Pascal-Antoine Christin, Michael Wallace, Gemma Martin, Michael Charles, Glynis Jones, Mark Rees and Colin P. OsborneThe lead author (C. Preece) working in the greenhouse growing crops and their wild ancestors. Photo credit – Catherine Preece.

Humans began farming the land 10,000 years ago, leading to an agricultural revolution, which had big impacts on human societies. The plants that we now use as crops have changed a lot since the first farmers started growing them. During the process of domestication, these plants changed in appearance and the amount of food that they produce increased. However, we do not fully understand how these changes happened. A deeper understanding of the origins of agriculture may prove useful for improving food production today.

We grew traditional versions of crops including wheat, barley, lentils and peas, and compared them with their wild ancestors, to see how they have changed through domestication, measuring a much wider range of characteristics than ever before. We found that crops are able to produce more food for us because of three important characteristics: they grow into bigger plants, they have larger seeds and they contain less non-edible material. Crops are also able to produce the same number of seeds as their wild ancestors, despite the seeds being bigger. This is important because normally plants must choose between producing a few big seeds or lots of small seeds, but this does not seem to apply so much to these plants.

Today we are seeing increasing pressure on global food production, and crop breeders are taking an increasing interest in traditional crops as a source of useful traits that may help to increase yields or increase resilience to climate change. Our work should help in this process by providing new insights into the process of crop domestication, which may lead to innovations in modern agriculture.

Image caption: The lead author (C. Preece) working in the greenhouse growing crops and their wild ancestors. Photo credit – Catherine Preece.
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Consequences of a nectar yeast for pollinator preference and performance

Robert N. Schaeffer, Yu Zhu Mei, Jonathan Andicoechea, Jessamyn S. Manson, and Rebecca E. IrwinBumblebees. Image provided by authors.

Pollinators provide essential services in natural and agricultural systems, driving global floral diversity and a significant percentage of food production. At the heart of interactions between plants and pollinators are key floral resources, such as nectar, produced by plants as a reward in exchange for pollination services provided. Comprised mostly of sugars and amino acids, this nectar reward can vary considerably in quality, and pollinator foraging decisions are frequently driven by nectar quality. Recently, considerable attention has been paid to the fact that microorganisms such as yeasts and bacteria often colonize nectar. These microorganisms consume nectar sugars and amino acids, altering the nutritional quality of this key resource. The consequences of these changes for pollinator foraging preferences and reproduction are poorly understood.

Here, we demonstrate that microorganisms in nectar, in particular the yeast Metschnikowia reukaufii, can significantly affect pollinator foraging decisions. Through a series of behavior experiments, we show that the yeast M. reukaufii may act as an honest signal, indicating the availability of nectar to common eastern bumble bee Bombus impatiens workers. Both naïve foragers, with no previous exposure to yeasts, as well as foragers trained to associate yeast with a flower color, used cues associated with yeast to make foraging decisions, actively seeking out yeast-inoculated flowers. However, miniature bumble bee colonies that consumed nectar containing active yeast or dead yeast did not differ in their reproductive performance, even when given a protein-limited diet, suggesting no apparent benefits or costs of yeast for bumble bee fitness.

Taken together, our results suggest that nectar yeasts can enhance floral signaling as well as alter foraging behavior at individual flowers, though these microorganisms may have no direct effect on pollinator performance. Thus, nectar yeasts may play a significant role in mediating pollinator foraging behavior, with consequences for plant fitness and evolution of floral traits.

Image caption: Bumblebees. Image provided by authors.
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Herbivore-specific induction of defence metabolites in a grass-endophyte association

Benjamin Fuchs, Markus Krischke, Martin J. Mueller & Jochen KraussPhysical conditions of the plants four weeks after herbivore introduction. Weekly clipped plants show fresh green leaf material after cutting. Aphid treated plants turn towards a yellowish colour, while locust treated plants show reduced leaf material compared to control plants.

Plants have developed several strategies for defence against pathogens and herbivores. The production of chemical compounds is a successful defence strategy to minimise herbivory. Chemical defence can range from deterrence or intoxication of herbivores up to the attraction of natural enemies of herbivores. A key feature of many chemical defence strategies is the induced production of chemical defence compounds following herbivore attack.

Symbioses (mutually beneficial interactions) between plants and microorganisms can alter the defence strategies of plants, increasing their defence against herbivores. The symbiosis between cool season grasses and endophytic fungi of the genus Epichloё is an example where a plant symbiotic microorganism affects herbivory on its host plant. Epichloё endophytes infect the above ground parts of many cool season grass species and produce toxic, herbivore deterring alkaloids. However it is unclear whether these alkaloids can be induced by herbivory and whether herbivore specific plant damage affects the production of specific alkaloids.

Our study organism was the cool season grass Lolium perenne infected with the endophytic fungus Epichloё festucae var. lolii which produces three bioactive alkaloids: peramine, which deters invertebrate herbivores, and lolitrem B and ergovaline, which are both toxic to vertebrate herbivores.

In a controlled common garden experiment we tested the effects of three different herbivore treatments, and a control treatment, on the growth of the endophytic fungus and the production of alkaloids over 18 weeks. We showed that the concentration of the vertebrate toxic alkaloid lolitrem B increased following clipping (a simulation of grazing herbivores), while the insect deterring alkaloid peramine increased following locust herbivory (biting-chewing herbivores). Aphids (piercing-sucking herbivores) affected neither alkaloid production nor endophyte growth.

Our study provides evidence for an herbivore-specific induction of chemical defence compounds from a grass endophyte following herbivore attack on its host grass. Our results indicate a close chemical crosstalk between the interacting species of a grass-endophyte symbiosis.

Image caption: Physical conditions of the plants four weeks after herbivore introduction. Weekly clipped plants show fresh green leaf material after cutting. Aphid treated plants turn towards a yellowish colour, while locust treated plants show reduced leaf material compared to control plants.
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Cannibalism or burial: undertaking behaviour depends on the change of death cues in termites

Qian Sun, Kenneth F. Haynes, Xuguo ZhouA termite worker consuming a dead worker. Taken by Hu Li.

The ability to detect environmental cues is important for animals to exploit resources and defend themselves against predators and disease. Social insects frequently encounter the dead bodies of their nestmates, which may carry pathogens and could cause an outbreak in the colony. Many social insects dispose of the corpses with a stereotypic behaviour named undertaking behaviour. Ants and honeybees remove the corpses from the nest, but termites that feed on a nutritionally imbalanced woody diet could benefit from recycling rather than discarding nutrients from dead nestmates. Therefore, corpses represent both a food resource and a pathogen risk for termites. As corpses decay with time, the reward from feeding declines and the risk of disease increases. The central goal of our study is to determine how termites regulate this trade-off by detecting chemical cues from corpses. We combined behavioural and chemical analyses to address this question using the eastern subterranean termite, Reticulitermes flavipes.

We found that termites cannibalize the corpses if they are freshly killed, but resort to burying them when the corpses are highly decayed. Such a behavioural switch is mediated by the changes of death cues released by the corpses. Immediately after death, corpses release 3-octanol and 3-octanone. The early death volatile cue, consisting of this alcohol possibly in combination with the ketone, attracts workers to quickly retrieve and consume the bodies, but the two compounds decrease rapidly with time. Correspondingly, there was an accumulation of late death cues, including a blend of phenol and indole, which enable termites to locate the corpses, and a blend of six fatty acids that trigger burial behaviour. Cannibalism is more efficient than burial behaviour, because it requires fewer workers, and also allows termites to recycle nutrients. However, if corpses are not found within the recyclable time frame, burial behaviour could effectively prevent pathogenic propagation.

Our study indicates that the dynamic changes in death cues balance nutritional rewards and infection risks. This post-mortem communication highlights unique adaptations in termites to their feeding habit and social living.

Image caption: A termite worker consuming a dead worker. Taken by Hu Li.
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Bad boys bite, good girls eat their dinner

Alexis Y. Dollion, G. John Measey, Raphaël Cornette, Liza Carne, Krystal A. Tolley, Jessica M. da Silva, Renaud Boistel, Anne-Claire Fabre and Anthony Herrel Image provided by authors.

Cranial morphology is complex and how it evolves remains relatively poorly understood. One of the complicating issues is that the head serves many functions ranging from the protection of the brain and major sensory organs to the control of feeding and drinking, and display and communication. These different functions often impose different and conflicting pressures on the size and shape of the cranium in vertebrates. An additional complicating factor is that the selective factors driving the evolution of cranial shape may differ in males and females. Indeed, whereas in males of many vertebrates, and especially lizards, the head is used in territory defense and male-male combat, this is typically not the case in females. Here we explore these issues in a group of dwarf chameleons from South Africa. We quantify skull, mandible and quadrate shape in 3D using a cross-sectional imaging technique (computed tomography, or CT imaging) and test whether skull shape is related to diet as determined by stomach flushing and maximal bite force capacity. Our results do indeed show strong correlations both between shape and bite force, and between shape and diet. Bite force is also related to diet. However, the observed patterns differ between males and females and suggest that the role of the cranium is not identical in both sexes. Our results shed light on the relevance of sex when relating a lizard’s morphological adaptations to its ecological role, and show the importance of collecting comprehensive data on shape, bite force and diet to unravel the selective pressures that govern the evolution of complex integrated structures such as the skull.

Image caption: Image provided by authors.
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How plant species colonize open spaces in meadows

Alena Vítová, Petr Macek and Jan LepšColonization of artificially created gap bounded by mesh after one year of monitoring. Photo provided by authors.

Most grasslands in Central Europe are dependent on human management. Their species composition and abundance have been shaped by centuries of regular mowing and pasturing. Small-scale local disturbances referred to as gaps are open to colonization and are often connected with management (a side-effect of machinery during mowing), or animals (burrowing animals, wild boar). Many meadow species efficiently colonize these gaps, some immediately after gap formation and some gradually over time. Meadow communities are thus dynamic systems containing gaps of various ages, each often differing in their species composition, forming a mosaic in space and time. Gap dynamics play an important role in the maintenance of meadow species diversity, which may be extremely high in some meadows. Nevertheless, species-specific information about dynamics of gap colonization is rather scarce. We aimed to disentangle the processes involved during gap colonization through a manipulative experimental approach in which we artificially created gaps.

Species can colonize gaps either vegetatively by rhizomes and other vegetative sprouts (from nearby in the neighbourhood), or by seeds which may be stored in the seed bank or that arrive via seed rain. We manipulated vegetative propagation into gaps by felting, and altered the seed bank using gamma radiation. We then followed the colonization of gaps by four main species groups with contrasting regeneration strategies (forbs [dicots, or broad-leaved plants], rushes [Juncaceae], grasses [Poaceae], and sedges [Cyperaceae]) over the following three years.

Initially, gaps were colonized mostly from seeds, with vegetative propagation dominating at later stages. There were also differences among species groups. Forbs regenerated mostly from the seed bank and were the first colonizing species. Later in the season, the seed rain also became important and resulted in a shift in species composition from forbs to grasses. The presence of a seed bank was essential for some species, and its presence in gaps had a consistent positive effect on species richness throughout the entire experiment. Gaps in meadow communities are very important for species regeneration via seed and the maintenance of species diversity, although species groups differ in their ability to colonize open spaces through time.

Image caption: Colonization of artificially created gap bounded by mesh after one year of monitoring. Photo provided by authors.
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Aphid toxicity to ladybeetles is not a function of host plant or facultative bacterial symbionts

Jennifer A. White, Joshua S. McCord, Kelly A. Jackson, Allison C. Dehnel, Paul A. LenhartSibling Harmonia axyridis larvae fed on toxic (top) or nontoxic (bottom) aphid lineages.  Larval age and image magnification are the same between panels.

For generalist predators that consume many types of prey, the world is complicated. Some prey species are reliably and consistently edible, but others are not. The multicolored Asian ladybeetle, Harmonia axyridis, is an invasive predator, but also an important biological control agent because it consumes a wide range of pest aphid species. One such pest, the cowpea aphid (Aphis craccivora), is extremely variable in its suitability as food for the ladybeetle. For decades, it has been known that cowpea aphids collected from locust trees (Robinia species) are toxic and can kill ladybeetles, whereas cowpea aphids from other host plants (such as vetch or alfalfa) can be perfectly good food. It is easy to assume that the toxicity of locust-feeding aphids is caused by locust; many other herbivorous insect species acquire chemical compounds from their host plants that they use in their own defense. Because different plant species vary greatly in their chemistry, it would make sense, then, that cowpea aphids from different plants would have different defensive properties. However, here we show that host plant doesn't affect the toxicity of cowpea aphid lineages. Toxic lineages that were originally collected from locust remain toxic even when the aphids had been feeding on vetch or alfalfa, and nontoxic lineages originally collected from alfalfa remain nontoxic even when feeding on locust. So, if current host plant has nothing to do with toxicity, why are toxic aphids consistently associated with locust trees in nature? We show that this is a correlative effect: the toxic aphid lineage is also infected with a heritable bacterial symbiont, Arsenophonus, which we've shown in previous studies to improve aphid performance on locust, but decrease performance on other plant species. Here we show that Arsenophonus doesn't cause aphid toxicity, because the toxic aphids retain their toxic properties even when cured of Arsenophonus. But because Arsenophonus happens to infect a toxic aphid lineage, aphids that do well on locust are also toxic. Our study therefore serves as a precaution that correlation does not necessarily mean causation, and establishes an interesting system to study how variation in prey defense affects predator populations.

Image caption: Sibling Harmonia axyridis larvae fed on toxic (top) or nontoxic (bottom) aphid lineages. Larval age and image magnification are the same between panels. .
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Diversity of ecological tasks in water fleas acts as a health insurance of lakes

Liisa Nevalainen and Tomi LuotoA fossil shell of a water flea (taxon Chydorus cf. sphaericus) extracted from lake sediment deposits. Photo credit: Liisa Nevalainen.

Human impact on lakes, most importantly agricultural land use and waste water draining, has continued for a long time, even for centuries in areas with prehistorical settlements, and has caused nutrient enrichment that may in severe cases lead to algae blooms and fish kills. Increase in nutrients, especially phosphorus, alters the structure of biological communities and how they function in lakes, for example what organisms eat and where they live. This may cause irreversible changes in how the lakes operate and act as resources for humans. Even though the state of lake pollution has improved during recent decades, the long lasting impact of agricultural land use close to lake margins has changed many lakes from their natural state. To understand how lakes operate and change during and after nutrient enrichment, we investigated 100-300 year old lake sediment deposits for water flea fossils for their occurrence and diversity of their specific tasks, such as feeding and habitats. Water fleas are microscopic crustacean animals that live in lake bottoms and open waters. Our study sites included two lakes with a similar history of nutrient enrichment caused by increased agricultural land use nearby. Our results suggested that water fleas occupying a range of different biological and chemical roles in lakes increase in the early stage of nutrient enrichment (~100-200 years ago) due to an increase in the variety of resources, such as different food items and habitats. When the lakes entered into even more nutrient rich conditions (mainly during the 20th century) as human impact continued, the interactions between nutrients and water flea functions varied between individual lakes, and were more related to the food web structure and presence of water flea consuming fish. Diversity of tasks in water fleas thus has a clear connection to lake productivity and food web structure in the historical period and recent decades. This makes the study of water fleas and their fossils in lake bottom sediments a promising tool to understand the long term health and recovery of lakes under human impacts.

Image caption: A fossil shell of a water flea (taxon Chydorus cf. sphaericus) extracted from lake sediment deposits. Photo credit: Liisa Nevalainen.
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Tree genetics strongly affect forest productivity, but intraspecific diversity-productivity relationships do not

Dylan G. Fischer, Carri J. LeRoy, Erika Hersch-Green, Clarissa Dirks, Randy K. Bangert, Gina M. Wimp, Joseph K. Bailey, Jennifer A. Schweitzer, Stephen C. Hartg, Gery Allan, Thomas G. WhithamTrees changing colour. Photo provided by authors.

Do more diverse mixtures of plants function more efficiently and take up more carbon? Previous studies have suggested this occurs frequently in grasslands when species are mixed. Other studies have now suggested that the same can be true of genetic mixtures within a species. When groups of plants are more genetically diverse, they might be more productive. Nevertheless, this idea requires that plants work together, and access resources differently, which may not always be true when looking at different genetic stock within a species. We conducted the first forest ecosystem-scale experiment designed to test if more diverse mixtures of genetic stock result in more productive forests. Our results suggest that they do not! We used a fast-growing cottonwood tree common to the Western USA, and found no effect of genetic stock diversity. We did, however, find enormous differences between different genetic monocultures. In fact, the differences between genetic stock of the same species were so big that they rivaled differences in productivity among forest biomes. In other words, one can go from the most productive forest in the world, to the least productive forest in the world, simply by changing the genetics of the tree. The accompanying photo by author Dylan Fischer shows trees in our experimental forest during fall when different genetic stock are clearly recognizable based on when the leaves change color. Gold-leaved trees represent one genotype of tree, and the larger green trees in the background are another genotype. Less productive trees drop their leaves earlier, even though all trees are the same species. The large observed differences in productivity demonstrate the importance of recognizing genetic variation within naturally occurring tree species, especially in novel climate environments.

Image caption: Trees changing colour. Photo provided by authors.
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Agricultural biodiversity enhances soil nutrient acquisition by crops

Wei-Ping Zhang, Guang-Cai Liu, Jian-Hao Sun, Dario Fornara, Fang-Fang Zhang, Li-Zhen Zhang and Long LiImage provided by authors.

Higher biodiversity is a key feature of intercropping systems, which involve the cultivation of two or more plant species at (about) the same time within the same agricultural field. Intercropping has been widely practiced in many parts of the world for thousands of years, especially in China, mainly because it promotes more efficient use of soil nutrients, water and light compared to monoculture crops, which is then associated with higher yields and a better use of agricultural land. Wheat/maize and barley/maize intercropping are long-established agricultural systems in arid northwest China, especially in areas where seasonal crop growth is significantly limited.

In this study, we addressed how rates of Nitrogen (N), Phosphorous (P) and Potassium (K) uptake might change through time between different agricultural systems. We compared temporal trajectories of N, P and K uptake by wheat, barley and maize in monocultures and intercropping. We asked how a high diversity of plant species might affect the acquisition of N, P and K uptake over time.

We found that maximum cumulative N, P and K uptake (kg ha-1) by wheat and barley were significantly greater in wheat/maize and barley/maize intercropping systems compared with wheat or barley monocultures. Similarly, maximum cumulative N and P (but not K) uptake by intercropped maize were significantly higher than in maize monocultures.

Wheat and barley plants reached their peak of daily N, P and K uptake rates at about 50 days after seedling emergence, whereas maize reached its peak of daily uptake rates at about 100 days after wheat emergence. This mismatch in nutrient uptake is evidence of an important temporal differentiation in nutrient use between these plants. Temporal differentiation in nutrient use between wheat or barley and maize was largely due to differences in the timing of sowing and harvesting of these species, which ultimately contributed to minimizing interspecific competition and the avoidance of negative effects of one crop on another. Our results suggest that ‘temporal complementarity’ in nutrient uptake by neighboring plant species is a key ecological mechanism, which contributes to overyielding (when a mixture of species yields more than you would expect from the yields of the individual species when grown in monoculture) and to higher plant nutrient uptake in intercropping systems.

Image caption: Image provided by authors.
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Accumulation of external nitrogen in decaying Norway spruce wood

Katja Rinne-Garmston, Tiina Rajala, Krista Peltoniemi, Janet Chen, Aino Smolander and Raisa MäkipääImage provided by authors.

Decomposition of dead wood, which is controlled primarily by fungi, contributes substantially to the long-lived forest carbon (C) pool and has a significant role in forest nitrogen (N) cycling. Because of the very high C:N ratios in decaying wood, the rates of N cycling processes and fungi-driven decomposition are tightly linked. External sources of N may be vital in establishing and maintaining high decomposition rates, due to the importance of N in the production of enzymes and fungal material. Wood N content has been found to increase during the decay process; however, the sources of this external N remain unclear.

To examine N dynamics of Norway spruce logs at various stages of decomposition, we combined a large variety of analytical methods: wood nitrogen isotope composition (δ15N), wood N content (N%), radiocarbon dating, fungal composition and fixation rate of atmospheric N2 into wood by bacteria. For N2 fixation rate we also determined its dependency on ambient temperature and decay class (i.e. extent of decay), when estimating annual N2 fixation rates for our study site.

N2 fixation was observed to have a major role in increasing wood N content during decay. For the most decayed wood it accounted for 60% of the total N accumulation. The calculated annual fixation rate was 85 g N/ha. Our δ15N model describing the sources of external N, statistical analysis and the fungal DNA composition of decayed wood suggest that other sources of external N accumulating in wood were soil foraging wood-decay fungi and mycorrhizal fungi.

Our study improves knowledge of the temporal dynamics of N accumulation in wood with advancing wood decay, the potential sources of external N and their relative significance. All of these factors are important for both nitrogen and carbon models that consider ecosystem responses to climate change.

Image caption: Image provided by authors.
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Healthy trees contain fungi that can recycle them back to soil

Zewei Song, Peter Kennedy, Feng Jin Liew and Jonathan SchillingDecay begins before life ends. Wood decomposer fungi Fomes fomentarius (white rot) and Piptoporus betulinus (brown rot) emerge from the same standing birch tree in Alaska. Jonathan Schilling.

Decomposition of wood is a process that recycles an immense global pool of aboveground carbon and that emits significant amounts of CO2 to the atmosphere. Predicting wood decomposition rates, however, is proving to be a challenge for modelers. Variability in these predictions is increasingly attributed to biotic variability (e.g. organism dynamics) rather than abiotic variability (e.g. climate) alone. Specifically, many studies show that altering the sequence of fungal inoculations in dead wood can steer decomposition in different directions, depending on which fungi arrive first. To a modeler, it might seem daunting that the fate of wood decay would rest, to a large extent, on timing. In nature, however, we know that certain fungi have rigid associations with certain trees (e.g. Piptoporus betulinus on Betula spp. trees) despite being flexible in laboratory trials. This indicates that wood decay may be more predictable than our dead wood inoculations might imply, and we hypothesize that this can be traced to fungi colonizing trees as endophytes (organisms living inside plants) prior to tree death.

To test the potential for these endophytic fungi to initiate and potentially dominate wood decay, we used laboratory microcosms to incubate stem sections cut from ten healthy birch trees. At time zero, there were 143 fungal taxa present in the wood, on average. After five months of incubation in isolation or in the presence of fungi inoculated to challenge the endophytes, the birch wood lost nearly two-thirds of its fungal endophyte taxa and became dominated by wood-degrading fungi. These endophytic wood-degrading fungi caused severe decay (30-40% wood mass loss) without any additional inoculum. Most surprising, however, was that although decomposition in the wood of all birch trees (ten replicates) was dominated by brown rot-type fungi, the dominant taxa did not include Piptoporus betulinus commonly found in decaying birch. Instead, wood decay was dominated (>90% relative abundance) by four taxa in the genera Coniophora and Postia – best known as pests in lumber. These results support our hypothesis that tree endophyte fungi can initiate and dominate wood decay with predictable outcomes, but it implies that these community-driven outcomes remain a function of environment.

 

Image caption: Decay begins before life ends. Wood decomposer fungi Fomes fomentarius (white rot) and Piptoporus betulinus (brown rot) emerge from the same standing birch tree in Alaska. Jonathan Schilling.
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Organic macromolecules and ultraviolet radiation combine in freshwater ecosystems to damage water flea DNA

Raoul Wolf, Tom Anderson, Dag Olav Hessen and Ketil HyllandImage provided by authors.

As a result of reduced acid rain, climate change, and increased vegetation cover, many lakes and rivers in boreal regions currently experience a phenomenon called “browning”. It describes an increasing transport of plant-derived material from terrestrial plants and soil into freshwater, which causes a distinct brown color. The substances responsible for this browning are usually organic macromolecules or humic substances, commonly referred to as dissolved organic carbon, or simply DOC.

Plants and animals living in lakes and rivers can benefit from increased browning, as it protects them from harmful ultraviolet radiation (abbreviated UVR). However, UVR photons can also react with these DOC substances and produce so-called reactive oxygen species (ROS). These are harmful for all organisms, as they can damage cell membranes, proteins and DNA.

The aim of our study was to find out if the interaction of DOC and UVR in freshwater could produce ROS, and if these harmful substances could then cause DNA damage in an aquatic animal. The animals of choice in our experiments were freshwater water fleas of the species Daphnia magna. Despite their name, water fleas are crustaceans and important members of freshwater food webs, and commonly used model organisms. In our experiments, the water fleas were put in artificially browned waters and put under artificial UVR sunlamps.

We found that by themselves, either DOC or UVR produced only modest amounts of harmful ROS, which caused only minor DNA damage in the animals. However, the combination of DOC and UVR resulted in substantial production of ROS, which caused high levels of DNA damage in Daphnia. This points out the importance of indirect and unsuspected effects, by which climate change may affect aquatic organisms.

Image caption: Image provided by authors.
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Accelerometers can measure total and activity-specific energy expenditure in free-ranging marine mammals only if linked to time-activity budgets

Tiphaine Jeanniard-du-Dot, Christophe Guinet, John PY Arnould, John R. Speakman, Andrew W. TritesAntarctic fur seals. Image provided by authors.

How much energy animals spend during their daily life and how they spend their time are two key factors in understanding their health and their ability to survive and produce viable young in the wild. However, this is really difficult to study in wild marine animals at sea. Recently, biologgers have allowed us to remotely track and record behaviours of these animals in their natural environment. Particularly, the use of accelerometers capable of recording 3D movements and posture of marine mammals at a sub-second resolution have opened a window onto the secret life of these animals over periods of weeks to months.

The theory that an animal’s movements, i.e. its body acceleration, are directly linked to the energy needed to perform them has found growing interest within the scientific community as it can provide a relatively easy and inexpensive way of measuring metabolic rates. This link has been tested and validated in various birds, sharks and mammals, mostly in controlled ‘laboratory’ settings. However, it is still uncertain whether the same relationships hold in wild conditions when animals perform a wide range of behaviours and activities (diving, traveling, grooming and sleeping). Consequently, we investigated whether animals’ dynamic body acceleration could accurately predict the energy expended by free-ranging marine predators during full trips at sea.

To do so, we equipped 25 lactating northern and Antarctic fur seals with accelerometers, GPS and time-depth recorders, and simultaneously obtained a reference measurement of total energy expenditure. We then compared measures of dynamic body acceleration of animals with their own energetic expenses. Our results show that acceleration was not a good predictor of fur seals’ energy expenditure over a full foraging trip at sea. However, accuracy of the link between acceleration and energetics increased greatly when analysed by type of activities separately at sea. Our study confirms that acceleration is a promising way to estimate energy expenditures of free-ranging marine mammals at a fine scale, but that it needs to be based on how animals partition their time between different activities rather than being derived as a single measure applied to entire foraging trips.

Image caption: Antarctic fur seals. Image provided by authors.
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The Ecology of De-Extinction

De-extinction and evolution

Alexandre Robert, Charles Thévenin, Karine Princé, François Sarrazin and Joanne ClavelPhoto credit: Alexandre Robert.

Some biologists suggest that they can recreate long lost creatures and bring revived lineages back into suitable habitats. However, the potential for this de-extinction process to contribute effectively to the conservation of biodiversity remains unexplored, especially from the perspective of evolution. We discuss the application of the existing evolutionary conservation framework to potential de-extinction projects. We aim to understand how evolutionary processes can influence the dynamics of resurrected populations, and what the potential evolutionary benefits of de-extinction are. In programs aiming to revive long-extinct species, the most important constraints to the short-term dynamics of any resurrected population are their intrinsically low potential to grow and persist, and their poor adaptation to biotic and abiotic changes in the recipient environment. Assuming that some populations of resurrected species can persist locally, they have the potential to bring substantial benefits to biodiversity if the time since initial extinction is short relative to the time scale of evolution. The restoration of lost genetic information could lead, along with the re-instatement of lost ecological functions, to the restoration of some evolutionary patrimony and processes, such as adaptation. However, substantial costs might occur, including unintended ecological and evolutionary changes in the local system, and unintended spread of the species. Further, evolutionary benefits are limited because extinct species that are original from an evolutionary point of view might be those for which de-extinction is the most difficult to achieve practically. Further, the resurrection of a few extinct species does not have the potential to conserve as much evolutionary history as traditional conservation strategies, such as the reduction of ongoing species declines. De-extinction is a stimulating idea, which is not intrinsically antagonistic to the conservation of evolutionary processes. However, poor choice of candidate species, and most importantly, lengthy time scales between a species’ extinction and its resurrection are associated with low expected evolutionary benefits and likely unacceptable ecological and evolutionary risks.

Photo credit: Alexandre Robert.
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The Ecology of De-Extinction

A mammoth undertaking: harnessing insight from functional ecology to shape de-extinction priority setting

Molly Hardesty-Moore, Douglas McCauley, Benjamin Halpern and Hillary YoungImage provided by authors.

De-extinction, or the process of resurrecting extinct species, is an idea that once only seemed possible in science fiction films. Rapidly advancing technologies, however, are bringing de-extinction within reach. Most of the scientific discussion of de-extinction has been focused on the methods that could be used to make it operable and the ethics surrounding whether it is right or wrong to bring back once-extinct species. If made successful, de-extinction could prove an interesting new tool for ecologists and conservation biologists. From an ecologist’s vantage point, the great risk in de-extinction is that it becomes overly focused on the fabrication of species that look like once-extinct species – but do not act like them. In this paper we critically evaluate how de-extinction as a science would have to evolve in order to become a tool of strategic value to ecological communities and ecosystems.

We suggest three ways that de-extinction can produce species that resurrect the ecological jobs of extinct species with high fidelity. First, select candidate species that played a unique role in ecosystems and their loss is more likely to have left gaps in the operation of living systems that have not yet been filled. Second, concentrate on species that went extinct recently, rather than older extinctions. Ecosystems change, and the more time that passes the harder it will be for once extinct species to step back into ecosystems and assume their former roles. Lastly, work only with species that de-extinction can bring back to historic abundance levels, because abundance and ecological performance are often tied together. Following this playbook can help ensure that de-extinction does more than produce ecological zombies.

Image caption: Image provided by authors.
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Stomatal regulation and efficient xylem water transport regulate diurnal water and carbon balances of tropical lianas

Ya-Jun Chen, Stefan A. Schnitzer, Yong-Jiang Zhang, Ze-Xin Fan, Guillermo Goldstein, Kyle W. Tomlinson, Hua Lin, Jiao-Lin Zhang and Kun-Fang CaoHuge lianas in tropical forest (photo by Chen YJ).

Lianas are a conspicuous component of tropical and subtropical forests, contributing up to 35% of woody plant diversity and 40% of stem density. Lianas are considered to be structural parasites because they use the stems of other plants (mostly trees) to ascend to the forest canopy, readily thrive and form a carpet-like leafy layer with little vertical structure, where they can get better position in terms of light. However, lianas have to cope with high light, high temperature, and high wind—all of which increase water stress, to which lianas are reported to be vulnerable due to their extremely wide and long water-conducting vessels. How lianas adapt to water stress and balance daily carbon fixation and water use have rarely been tested empirically to date.

Here we selected four liana and five tree species that co-occur in a tropical forest in southwest China. Specifically, we tested whether physiological regulation can help lianas mediate the diurnal water and carbon balances during the day. Lianas tend to run a more “risky” hydraulic strategy. They appear to have low water storage capacity and are vulnerable to daily water deficit due to their wide vessels and slim stems. However, physiological regulation and efficient water transport from the soil to terminal branches could help lianas maintain their stem water status within a safe range to avoid excessive water loss. Therefore, we provide experimental evidence for physiological adaptation of lianas to a hot/dry environment that may help explain how lianas operate efficiently in tropical seasonal forests.

Image caption: Huge lianas in tropical forest (photo by Chen YJ).
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Adaptation to heat stress reduces plasticity in a marine copepod

Morgan. W. Kelly, M. Sabrina Pankey, Melissa .B. DeBiasse and David.C. PlachetzkiTigriopus californicus (female).

Human-driven climate change is a major threat to global biodiversity. For species that are able to do so rapidly enough, evolutionary adaptation may provide some protection against changing environments. Organisms may also respond to changing environments via physiological acclimation, and this too may buffer some populations from extinction. However, while both are potentially beneficial, these two responses may either dampen or strengthen each other’s effects, and little is known about how they are likely to interact during periods of environmental change. We examined the effects of adaptation to heat stress on the ability to acclimate to this stressor in the crustacean Tigriopus californicus. We artificially selected populations for increased heat tolerance in the lab, then measured heat tolerance and the ability to acclimate to heat stress in both selected populations and controls. We also measured the gene expression response to heat stress in both populations. We observed increased heat tolerance in experimentally evolved animals, but also diminished ability to acclimate to heat, and a smaller gene expression response to this stressor. Our findings have important implications for biological responses to climate change: if adaptation to environmental stress reduces the ability to acclimate, then sensitive populations may not be able to count on the benefits of both adaptation and acclimation as buffers against climate change.

Image caption: Tigriopus californicus (female).
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A global method for calculating plant CSR ecological strategies applied across biomes worldwide

Simon Pierce, Daniel Negreiros, Bruno E.L. Cerabolini, Jens Kattge, Sandra Díaz, Michael Kleyer, Bill Shipley, S. Joseph Wright, Nadejda A. Soudzilovskaia, Vladimir G. Onipchenko, Peter M. van Bodegom, Cedric Frenette-Dussault, Evan Weiher, Bruno X. Pinho, Johannes H.C. Cornelissen, J. Philip Grime, Ken Thompson; Roderick Hunt, Peter J. Wilson; Gabriella Buffa, Oliver C. Nyakunga, Peter B. Reich Marco Caccianiga, Federico Mangili Roberta M. Ceriani, Alessandra Luzzaro, Guido Brusa, Andrew Siefert, Newton P.U. Barbosa, F. Stuart Chapin III, William K. Cornwell, Jingyun Fang, G. Wilson Fernandes, Eric Garnier, Soizig Le Stradic, Josep Peñuelas, Felipe P. L. Melo, Antonio Slaviero, Marcelo Tabarelli, Duccio TampucciImage provided by authors.

A vast range of plant biodiversity exists on Earth, with each species characterised by a particular suite of morphological traits. However, not all traits affect survival and many operate only during brief moments of the life-cycle. Plants exhibit a surprisingly limited number of basic ways in which they can use available resources to grow and persevere: differences in plant size affect the outcome of competition, and differences in the ‘economics’ of how plants invest resources – in individual robustness or in reproduction – determine how plant populations persist during environmental difficulties. Much of biodiversity represents variation around these general themes, or primary ‘strategies’.

Certain size and economics traits that can represent primary functioning, such as leaf size and aspects of photosynthetic tissue density, have now been measured around the world and can potentially provide a global framework within which strategies can be measured and compared. These absolute limits are used here to develop a tool for plant strategy classification, grounded in a theory of plant strategies (competitor, stress-tolerator, ruderal, or ‘CSR’, theory).

As plant adaptation within different geographic regions is intimately linked to climate (particularly temperature and seasonal water availability) there is reason to expect plant strategies to vary at the largest scales, between bioclimatic regions or biomes. The global CSR analysis method was used to analyse the range and character of plant strategies in all 14 major biome classes worldwide. The results did demonstrate differences in functional specialisation between biomes but also detailed a large amount of variability within biomes, probably due to the presence of contrasting habitats and plant communities within each one. However, it is clear that the global ‘CSR analysis’ tool presented here is valid for the functional description of plant species and communities worldwide, and can provide plant ecologists working in different habitats and biomes with a lingua franca equivalent to taxonomists’ use of Latin.

Image caption: Image provided by authors.
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Importance of deep water uptake in tropical eucalypt forest

Mathias Christina, Yann Nouvellon, Jean-Paul Laclau, Jose L. Stape, Jean-Pierre Bouillet, George R. Lambais , Guerric le MairePhotograph provided by authors.

Water uptake by deep roots is generally considered to be an efficient means of adapting to drought in tropical and subtropical forests. Although fine root biomass generally decreases exponentially with depth, with fewer than 10% below a depth of 1 m, many tree species can grow roots to depths of more than 10 m with maximum rooting depths reaching about 60 m for eucalyptus trees. Despite their low biomass, deep roots are likely to have a strong effect on the functional ecology of forest ecosystems.

There is a lack of in situ measurements investigating the multiple interactions between rainfall patterns, water fluxes in the soil, water table dynamics, root growth, and the dynamics of water uptake by tree roots down to the root front (maximum root depth) in tropical forests. Simple forest ecosystems such as Eucalyptus plantations may provide useful information on the belowground strategy of fast-growing trees, and more generally on the consequences of deep rooting patterns for tree water use in tropical forests.

The aim of this study was to explore the multiple functions of deep rooting profiles in terms of drought avoidance strategy and use of transient water resources, based on long term experimental and modelling analyses in a eucalypt plantation. Our study provides a quantification of water withdrawal throughout the whole rooting profile, including the interaction with the water table, in a planted tropical forest over an entire cultivation cycle of five years. We show that deep water uptake (3 to 16 m depth) is critical to explain the high transpiration rates throughout the year, with different mechanisms involved at different growth stages. Possible insights into the role of deep roots in tropical forests are discussed, as well as the impact of deep rooting on large scale ecosystem services.

Image caption: Photograph provided by authors.
Read the article in full here.

 

Conserving rare species when de-extinction is an option

Gwenllian Iacona, Richard F. Maloney, Iadine Chadès, Joseph R. Bennett, Philip J. Seddon, Hugh P. PossinghamThe Huia (Heteralocha acutirostris), is an extinct New Zealand bird species with an interesting dimorphism such that the female has a dramatically longer bill than the male. The last individuals may have survived until as recently as the 1960s. Species such as this are often suggested as candidates for de-extinction: they are recently lost species of significant conservation interest, and the threats that caused their extinction are known. This paper discusses how using a decision theory approach to conservation prioritization can help managers decide if de-extinction of such species is a good idea.   – photographer J.L . Kendrick. Photo courtesy of the New Zealand Department of Conservation.

The technology to revive extinct species (de-extinction) may soon no longer be simply in the realm of science fiction. In the exciting rush to bring back populations of wild mammoths, or moa, or passenger pigeons, we need to take a step back and make sure that the conservation benefits of such an action outweighs any potential perverse negative impacts. We suggest that the decision tools used in modern conservation prioritization approaches can quantitatively and transparently weigh the pros and cons of de-extinction. This is especially relevant to managing a de-extinct species in the wild in systems where there are extant species of conservation concern. While outlining the steps to the process, we discuss the new considerations that would be important if de-extinction was a possible conservation action. One particularly interesting implication of de-extinction would be its capacity to change the biodiversity conservation problem from the current one that is similar to managing non-renewable natural resources, to a version where the management is of a potentially renewable natural resource. This switch opens up a new suite of time preference and risk aspects to rare species management which could change the strategies employed by managers and the possible conservation outcomes. We are not arguing for or against de-extinction. Instead, we are proposing that the technological advances need to be considered within the context of the existing conservation landscape, and that such considerations may include unprecedented modifications to the current species prioritization problem.

Image caption: The Huia (Heteralocha acutirostris), is an extinct New Zealand bird species with an interesting dimorphism such that the female has a dramatically longer bill than the male. The last individuals may have survived until as recently as the 1960s. Species such as this are often suggested as candidates for de-extinction: they are recently lost species of significant conservation interest, and the threats that caused their extinction are known. This paper discusses how using a decision theory approach to conservation prioritization can help managers decide if de-extinction of such species is a good idea. – photographer J.L . Kendrick. Photo courtesy of the New Zealand Department of Conservation.
Read the article in full here.

 

Root heterogeneity along an arctic elevational gradient: the importance of resolution

Sabrina Träger & Scott D. WilsonRoots in arctic forest in a minirhizotron image (13.5 x 18 mm). Photo by S. Träger.

The majority of ecological studies focus on aboveground parts of plants and their interaction with the environment. However, plant roots often account for 80 – 90 % of plant biomass, especially in the Arctic. Roots are the key link providing plants with nutrients and water, and providing organic carbon to soils. Patchy distribution of resources can lead to and in turn be influenced by patchy root growth.

The magnitude and spatial scale of root patchiness varies with the dominant vegetation type (e.g. forest or grassland). However, studies are limited to temperate regions and deal with scales ranging between a few kilometers to a few centimeters. At the same time, the root diameter and thus the scale of interaction with the environment can be as small as fractions of a millimeter. Knowledge about root patchiness at those scales is still missing.

We analyzed the magnitude and scale of fine root patchiness in the Arctic at resolutions ranging from 1 to 300 mm² along an arctic alpine gradient (500 to 1100 m above sea level) to cover a variety of vegetation types (from forest to tundra). To study roots in their natural environment and in a non-invasive way we used a minirhizotron camera.

Roots in all vegetation types responded to or generated very fine scales of spatial patchiness of a few millimeters, which are scales about five times smaller than those that have previously been found. The patchiness of roots was greatest at the highest elevation, tundra, where the smallest plants dominated, which stands in contrast to studies from temperate regions where patchiness increases with plant size. Both the magnitude and scale of heterogeneity varied with sampling resolution, suggesting resolutions as small as a few millimeters are relevant to studies of spatial root interactions and belowground processes.

Image caption: Roots in arctic forest in a minirhizotron image (13.5 x 18 mm). Photo by S. Träger.
Read the article in full here.

 

Effects of flooding on relationships between plants and soil fauna

Corentin Abgrall, Matthieu Chauvat, Estelle Langlois, Mickaël Hedde, David Mouillot, Sandrine Salmon, Bruna Winck and Estelle ForeyView of the considered flooding gradient from the mudflats (photo credit: Estelle Langlois-Saliou).

Terrestrial ecosystems are composed of plants and soil animals (e.g. earthworms, small insects) with strong interactions between them that are central in ecosystem functioning. These interactions between plants, soil organisms and the soil itself regulate processes such as nutrient cycling or energy flow and control how plant and animal communities are structured. Simultaneous study of all these compartments can therefore provide additional information on how the ecosystem is structured and functions, more so than separate studies ever would. In this study we looked for links between plant and soil fauna characteristics (or traits) in relation to soil abiotic properties along a flooding gradient on the banks of the Seine River. Small and localized environmental gradients such as this one provide powerful tools to assess the effects of variations within a specific environmental variable (here flooding) on various processes. We sampled and identified soil fauna and plants in the field and used publically available databases to provide information on their traits. We observed a strong influence of flooding on the structuring of plant communities with particular traits, or adaptations, being selected by flooding intensity leading to the existence of functionally, and visually, different communities along the gradient. Springtails, small soil arthropods which we used as a proxy for the soil fauna, were not observed to be directly linked to variations in flooding intensity. Instead of being directly filtered by flooding, springtail traits were selected and filtered by variations within plant communities, especially their traits. We thus revealed an indirect influence of flooding intensity on soil fauna through its effects on plant communities. As this pattern has been previously observed for other gradients and species, our results enhance our understanding of how naturally-occurring communities can be influenced by other organisms as well as their physical and chemical environment.

Image caption: View of the considered flooding gradient from the mudflats (photo credit: Estelle Langlois-Saliou).
Read the article in full here.

 

Salivary cues: Simulated deer browsing induces changes in plant hormones and defense compounds in tree saplings

Bettina Ohse, Almuth Hammerbacher, Carolin Seele, Stefan Meldau, Michael Reichelt, Sylvia Ortmann and Christian Wirth Simulating deer browsing by clipping a tree sapling’s apical bud and applying deer saliva on the fresh cut (here on Acer pseudoplatanus). Photo by Bettina Ohse.

Young trees in temperate forests are often browsed by mammalian herbivores, such as deer. Studies on insect herbivory have shown that plants respond to herbivory by upregulating growth hormones and producing defense compounds. However, it remains unknown whether the same response mechanisms are induced when young trees are browsed by mammals. We also wanted to know if tree saplings can detect whether they are just injured mechanically, or whether they are browsed by deer. To answer these questions, we simulated deer browsing on field grown sycamore maple (Acer pseudoplatanus) and European beech (Fagus sylvatica) saplings by clipping their buds in winter and leaves in summer. For some of the saplings we additionally applied deer saliva with a pipette on the cut surface.

We found that two hours after clipping, wound hormones, called jasmonates, increased in the remaining maple buds and beech leaves. This is a well-known response to herbivory, but differed here between tree species and developmental stages. In maple buds, growth hormones (cytokinins) also increased after clipping, probably because if maple loses its one main apical bud through browsing, the upregulated growth hormones will help activate lateral buds for regrowth. Beech has more equal buds and may therefore not respond as strongly to clipping when losing one. Saliva application did not amplify wound hormone responses, but led to increased levels of the signaling hormone salicylic acid in beech leaves, suggesting that the trees were able to detect something in the deer saliva. Interestingly, changes in defense compounds were found only when deer saliva was also applied, which means that these compounds are only regulated specifically after deer browsing and not after any mechanical damage. Not all defense compounds changed in the same way. Mainly hydrolysable tannins increased, although they are not harmful to deer. Condensed tannins, which occurred only in beech and are known to be avoided by deer because they negatively impact digestion, did not change, and may rather act as a constitutive defense, i.e. one that is permanently present.

We conclude that tree saplings are able to detect and specifically respond to mammalian herbivory, although strategies to respond to mammalian browsing seem to be species-specific, probably based on distinct combinations of morphological and chemical characteristics.

Image caption: Simulating deer browsing by clipping a tree sapling’s apical bud and applying deer saliva on the fresh cut (here on Acer pseudoplatanus). Photo by Bettina Ohse.
Read the article in full here.

 

In, out or staying put? The landscape and the plant both have their say.

Alistair G. Auffret, Elsa Aggemyr, Jan Plue and Sara A.O. CousinsThe Stockholm archipelago from above (Photo: S. Cousins); Common Hepatica (Hepatica nobilis) responded well to grassland abandonment (Photo: A. Auffret);  However, Mountain Everlasting (Antennaria dioica) disappeared completely from the 27 islands  (Photo: A. Auffret); Harebell (Campanula rotundifolia) has characteristics of plants both able to persist and able to disperse (Photo: A. Auffret).

Every summer, Stockholm's idyllic archipelago is alive with tourists. People arrive at an island, stay for a while, and then leave. During the 20th century, the same has happened to the islands' plant species, albeit much more slowly. Up until the 1950s, the area was a busy farming landscape. Fodder was grown in the meadows and cattle were transported from island to island during the summer. Since then, agriculture has been almost totally abandoned and now most of the land area is covered in forest. This has had a huge impact on the area's plant life.

We compared species lists of plants from 27 small islands in 1908, when farming was still thriving, with our own survey from 2008. This meant that for each island, we were able to see which plant species had arrived, which had disappeared and which had stayed put during 100 years of landscape change. It was much easier for plants to survive on and arrive at larger islands and those close to the mainland, but it also depended on the plants themselves. Taller plants, which were able to compete for light in the overgrown pastures, could persist and spread to new islands, while plants with long life spans or long-lasting seeds were also more able to survive adverse conditions. Plant species that prefer to move (disperse) rather than stay put did not fare so well. Even if one would expect such species to move to more suitable areas following grazing abandonment, the magnitude of change meant that there was simply nowhere for them to go.

We also compared the species listed in the grid squares used for the historical and present-day plant atlases covering the same area. In this case it was only the plants, not the landscape, which explained change over time. Understanding how plants and animals are affected by human activity over time is interesting for ecologists, and historical species lists are therefore very useful. However, our results show that it is important to understand that different sources of species observations can affect the patterns we see and what drives them.

Image caption: The Stockholm archipelago from above (Photo: S. Cousins); Common Hepatica (Hepatica nobilis) responded well to grassland abandonment (Photo: A. Auffret); However, Mountain Everlasting (Antennaria dioica) disappeared completely from the 27 islands (Photo: A. Auffret); Harebell (Campanula rotundifolia) has characteristics of plants both able to persist and able to disperse (Photo: A. Auffret).
Read the article in full here.

Review

 

Bridging frameworks to better understand the nutrition of animals in their environment

Erik Sperfeld, Nicole Wagner, Halvor Halvorson, Matthew Malishev, David RaubenheimerThe water flea Daphnia magna (photo: Silvia Heim), the grasshopper Locusta migratoria (adapted photo by Ferran Turmo Gort, CC BY 2.0), and the caddisfly larvae Pycnopsyche gentilis (courtesy of Bob Henricks)..

It is essential for ecologists to understand the interaction between animal nutrition and the environment to better predict how animals will respond to our changing world. The research field investigating this animal nutrition-environment interface, nutritional ecology, has developed tremendously within recent decades. Steering this field are two prominent research frameworks, offering a toolbox of concepts to address the challenges of nutritional ecology. One framework, ‘Ecological Stoichiometry’ (ES), uses elements (e.g. carbon, nitrogen, phosphorus) to explore how imbalanced diets alter animal physiology, population dynamics, and nutrient cycling in ecosystems. The second framework, ‘Nutritional Geometry’ (NG), uses geometry to study feeding decisions of animals to maximize their fitness. ES originates from studies on element cycling, often using aquatic invertebrates (e.g. water fleas) as focal organisms, whereas NG originates from animal behaviour research, particularly on terrestrial insects (e.g. grasshoppers and cockroaches). Both origins have influenced the types of questions investigated and the type of nutrient currency used, with NG focusing on macronutrients (proteins, carbohydrates, and fats) and ES on elements.

Despite their inherently different perspectives, NG and ES are unified by a shared concept that contributes to collectively achieving the common goal of understanding the animal nutrition-environment interface. This concept, called homeostasis, drives animal nutrition and is broadly defined as an animal’s ability to regulate its internal nutrient status under a varying diet. ES uses an “are you what you eat?” approach to homeostasis by measuring internal nutrient composition, while NG adds individual behaviour to diet choice and food intake. In this paper, we illustrate how the complementary homeostasis approaches of NG and ES can be integrated in a conceptual, mathematical model that a) describes animal metabolism and tracks the flow of multiple nutrients through the body, and b) describes individual animal feeding behaviour in its environment in time and space. Our described modelling approach aims to advance nutritional ecology by better connecting organisms with their environments across different scales by using a shared concept well established in the field.

Image caption: The water flea Daphnia magna (photo: Silvia Heim), the grasshopper Locusta migratoria (adapted photo by Ferran Turmo Gort, CC BY 2.0), and the caddisfly larvae Pycnopsyche gentilis (courtesy of Bob Henricks)
Read the article in full here.

 

Experimental warming in a dryland community reduced plant photosynthesis and soil CO2 efflux, but didn't change the relationship between the fluxes

Timothy M. Wertin, Jayne Belnap and Sasha C. ReedClimate manipulation experiment in a semiarid grassland, with Achnatherum hymenoides (Indian ricegrass) as the focal plant species; photo by TM Wertin.

As air temperatures warm and precipitation patterns shift, arid and semiarid grasslands, such as those typical of the southwestern US, are expected to expand throughout this century. At the global scale, drylands support up to 38% of the human population, a number that is expected to increase due to both population growth and climate change. Recent research also suggests dryland systems are a major factor dictating future carbon cycling and climate. From a regional perspective, arid and semiarid grasslands represent critical habitat for wildlife, agriculture, and livestock grazing. If climate change affects plant growth, it would have dramatic implications on the landscape’s ability to sustainably maintain food production and carbon stocks.

Nevertheless, our understanding of how dryland grasses will respond to climatic change remains notably poor. To test the effects of warming on arid grasslands we conducted a climate manipulation study where we artificially increased plant and soil temperature by ~2 oC, which is well within the expected range of temperature increase expected for the Southwest. Specific goals of this experiment were to determine how a change in temperature would affect photosynthesis (the process by which plants convert solar energy and CO2 into organic forms) and soil respiration (the conversion of plant carbon and soil organic matter into CO2 and energy). We conducted this experiment on Indian Rice Grass, a native plant that is heavily relied upon for native and domesticated animal grazing.

Our study showed that a relatively subtle increase in temperature reduced both photosynthesis and soil respiration. The close coupling between soil respiration and photosynthesis was surprising; although warmer temperature reduced both fluxes, it did not change the relationship between the fluxes. In our study site, soil organic matter is quite low, and our data suggest that soil CO2 efflux was strongly regulated by newly acquired photosynthetic products respired or exuded by roots. This finding may have dramatic implications for climate models, which are used to predict carbon cycling and climate, and also heralds concern for the important grasses of the Southwest.

Image caption: Climate manipulation experiment in a semiarid grassland, with Achnatherum hymenoides (Indian ricegrass) as the focal plant species; photo by TM Wertin.
Read the article in full here.

The Ecology of De-Extinction

How close can we get to bringing an extinct species back to life?

Beth Shapiro A researcher prepares a fragment of mammoth bone for DNA extraction in the Paleogenomics Lab at UC Santa Cruz. Credit: Beth Shapiro.

Over the last five years, de-extinction, which is the term used to describe the idea that extinct species may soon be brought back to life, has received increasing attention in both scientific and public arenas. Discussions about de-extinction tend to concentrate on the ethical and political implications of resurrecting extinct species and, increasingly, to focus on the ecological consequences of releasing resurrected species into the wild. Relatively less attention has been paid, however, to the process of de-extinction itself, specifically whether the technology is sufficiently advanced to bring an extinct animal species back to life.

I review the three main technologies that are being considered at present for de-extinction: back-breeding, cloning via somatic cell nuclear transfer, and genetic engineering. Back-breeding aims to concentrate ancestral traits that persist within a population into a single individual using selective breeding. Cloning aims to create genetically identical copies of an extinct species from preserved cells, which means that this approach may not be feasible for long-dead organisms whose cells, and the genetic material within them, have decayed. Genetic engineering draws on recent advances in both ancient DNA and genome editing technologies, and aims to edit the genome sequence within a living cell so that the sequence more closely resembles that of a closely related extinct species. This edited cell would then be cloned, creating a genetic hybrid between the living and extinct species.

Because the phenotype of an organism is the consequence of the interaction between its genotype and the environment in which it develops and lives, none of these processes will create exact copies of the extinct species that they are attempting to resurrect. Precise replication, however, is not necessary to achieve the conservation-oriented goals of de-extinction. In the majority of ongoing de-extinction projects, the goal is to create functional equivalents of species that once existed: ecological proxies that are capable of filling the extinct species’ ecological niches. It is this application of de-extinction technologies that is likely to have the most positive impact on conservation.

Image caption: A researcher prepares a fragment of mammoth bone for DNA extraction in the Paleogenomics Lab at UC Santa Cruz. Credit: Beth Shapiro.
Read the article in full here.

 

Assessing vulnerability of functional diversity to species loss: a case in Mediterranean agricultural systems

Carlos P. Carmona, Irene Guerrero, Manuel B. Morales, Juan J. Oñate & Begoña PecoDetail of one of the agricultural fields included in the study.

Increasing intensification of land use is leading to biodiversity losses worldwide, which in turn can alter the functioning of ecosystems. Agricultural intensification aims to increase yield through changes in management both at the local field and at the landscape level. Arable plants, which support services like biological pest control, as well as the presence of pollinators, birds and mammals, are one of the groups most notably affected by these practices. However, it is increasingly clear that not all species are equally important for ecosystem processes. Approaches based on the traits of plants (e.g. height or leaf area) have allowed ecologists to tackle questions regarding the effects of plants on ecosystem functioning, because these traits determine how species affect different ecosystem processes. Thus, whereas the loss of a species with unique functional traits from a community may result in a reduction in the capacity of the community to perform some function, the loss of a functionally redundant species should have a much smaller impact. Assessment of the changes in functional trait diversity –a proxy of the range of functions provided by a community– as species are lost appears as a promising tool to predict the impacts of land use intensification. Here, we modified a recently developed method that compares the changes in functional diversity caused by random losses of species with those expected under the most likely order of species losses. This approach allowed us to estimate the vulnerability of the functional diversity of biological communities. We applied this method to arable plant communities from 78 agricultural fields in the area of Madrid (Spain), across a gradient of agricultural intensification. We found that the vulnerability of functional diversity to species losses increased along with agricultural intensification. Importantly, vulnerability to intensification was markedly non-linear, with great increases in the first stages of intensification, and much smaller increases afterwards. Our results suggest that field-level agricultural intensification not only reduces the taxonomic and functional diversity of arable plant communities, but also eliminates functionally redundant species, thus increasing their vulnerability to further species losses.

Image caption: Detail of one of the agricultural fields included in the study.
Read the article in full here.

 

Positive species diversity and above-ground biomass relationships are ubiquitous across forest strata despite interference from overstorey trees

Yu Zhang, Han Y.H. Chen, Anthony R. TaylorOld growth red spruce (Picea rubens) stand, typical of eastern Canadian temperate forest.  Photo Credit: Anthony Taylor.

There is growing concern over rates of global species diversity loss, given its important role in the healthy functioning of ecosystems and the many goods and services they provide. However, our knowledge of how diversity supports ecosystem function remains unclear. While positive relationships between tree species diversity and forest biomass production have been observed, forests are structurally complex, consisting of various understorey vegetation layers which also contribute to ecosystem functioning as they often account for the majority of species richness; however, the relationships between understorey vegetation diversity and function are largely unexplored. Further, few studies have simultaneously assessed how both overstorey and understorey vegetation interact and contribute to overall forest ecosystem function.

In our study, we used Canada’s National Forest Inventory data, covering many forest types across a wide spatial distribution, and a robust statistical modeling approach (structural equation modelling) to explore both overstorey and understorey relationships between species richness and forest biomass production while accounting for potentially confounding factors, including climate, physical site characteristics, and forest ageing. We found positive relationships between species richness and biomass production across all forest vegetation layers, but the relationship was strongest for the overstorey layer. Species richness of the understorey tree, shrub, and herb layers was positively related to overstorey species richness. However, overstorey biomass had a negative effect on the biomass production of all understorey layers. Our results suggest that resource filtering by overstorey trees might have reduced the strength of the positive diversity-productivity relationships in the forest understorey, supporting previous hypotheses that the magnitude and direction of diversity-productivity relationships is context specific and dependent on the conditions of the surrounding environment. Further, heterogeneity in understorey resources, as affected by overstorey trees, may promote niche complementarity (i.e. plants using different resources, or at different times or in different places) as the main mechanism driving diversity-productivity relationships in understorey vegetation.

Image caption: Old growth red spruce (Picea rubens) stand, typical of eastern Canadian temperate forest. Photo Credit: Anthony Taylor.
Read the article in full here.

 

Movement correlates of lizards' dorsal pigmentation patterns

Topaz Halperin, Liran Carmel and Dror HawlenaPhoto provided by authors.

The reasons why some animals have cryptic body patterns, such as spots, reticulations and blotches, while others have conspicuous stripes, has long intrigued scientists. We provide a simple explanation for this quandary that is based on the balance between the animal’s need to eat and the need to avoid being eaten. Species that remain still during much of their activity time, such as animals that hunt from ambush, may benefit from cryptic body patterns that help them blend in to the environment. However, cryptic patterns are less beneficial for species that actively search for food. This is because visual predators can easily detect a moving prey regardless of their coloration. Conversely, these highly detectable active species may benefit from conspicuous stripes that improve their chances to survive predator attacks. Stripes can dazzle the predator’s motion perception and hamper its ability to intercept escaping prey. Thus, we suggest that species that forage less actively should have cryptic patterns while species that actively search for food should have stripes. We tested this hypothesis by studying the association between lizard foraging behaviors and their pigmentation patterns. Using an extensive literature survey, we found that lizards with stripes were indeed substantially more active than lizards with cryptic patterns. Our findings provide the first quantitative support for the hypothesized relationships between pigmentation-patterns and foraging behavior. These findings might be relevant to other animals besides lizards. We hope that future studies will test our movement-patterns hypothesis, ultimately applying meticulous manipulations to tease apart and test its mechanistic details.

Image caption: Photo provided by authors.
Read the article in full here.

 

Searching for prey in a three-dimensional environment: hierarchical movements enhance foraging success in northern elephant seals

Taiki Adachi, Daniel P. Costa, Patrick W. Robinson, Sarah H. Peterson, Masato Yamamichi, Yasuhiko Naito and Akinori TakahashiFemale northern elephant seals during moulting season at Año Nuevo State Reserve, CA, USA. Photo taken by T. Adachi in the morning on May 23, 2011.

In nature, prey is often patchily distributed. Therefore, to enhance foraging success, predators are expected to concentrate search paths in areas where prey is more abundant. This style of searching is generally called “area-restricted search (ARS)”, which is characterized by sinuous search paths of predators with increased turning frequency. ARS has been suggested as an optimal search strategy in a patchy environment for both terrestrial and marine predators. However, due to the technological challenge of coupling search paths of animals with records of feeding events (prey captures), it remains unclear if ARS actually enhances foraging success in free-ranging animals, especially in marine animals that forage in a three-dimensional (3D) underwater environment.

Here, we reconstructed fine-scale 3D dive paths of a deep-diving (occasionally over 1000 m) marine predator, the northern elephant seal, coupled with recording feeding events using accelerometers attached on their jaws. Then, we quantified the 3D foraging behavior to test if seals enhance foraging success by employing “volume-restricted search” (VRS, termed for ARS in three-dimensions) while exploring a 3D environment.

Our results showed that most feeding events occurred when seals employed VRS. Also, we found that there was a hierarchical structure to the VRS; most small-VRS (95%) were nested within large-VRS (nested VRS). Importantly, nested VRS had significantly higher feeding rates than non-nested VRS, because nested VRS contained small- and large-VRS with higher and lower feeding rates, respectively. These results provided the first empirical evidence that underwater sinuous search paths (VRS) are strongly linked to higher foraging success, especially when the search paths are hierarchically structured, suggesting that seals forage on prey in a hierarchical patch system where high-density patches at small scales are nested within low-density patches at larger scales.

For all animals that search for prey, it is a central question how to adjust search paths according to the spatial distribution of prey to enhance foraging success. Our results suggest that northern elephant seals enhance foraging success by employing hierarchical decision making to concentrate search paths in areas where prey appeared to be hierarchically structured in patches over a range of 3D spatial scales.

Image caption: Female northern elephant seals during moulting season at Año Nuevo State Reserve, CA, USA. Photo taken by T. Adachi in the morning on May 23, 2011.
Read the article in full here.

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