Lay summaries for Volume 30, Issue 6 of Functional Ecology

 

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FE Spotlight

Plant physiological ecology

Plant-animal interactions

Animal physiological ecology

Behavioural ecology

Community ecology

 

FE Spotlight

Ecological significance of thermal tolerance and performance in fishes: new insights from integrating field and laboratory approaches. Ben Speers-Roesch and Tommy Norin

Plant physiological ecology

Trade-offs in juvenile growth potential vs. shade tolerance among subtropical rainforest trees on soils of contrasting fertility

Kerrie M. Sendall, Christopher H. Lusk and Peter B. ReichPhoto provided by authors.

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Coexistence of tree species is often associated with a trade-off between juvenile shade tolerance and growth rate in gaps. On the other hand, species sorting along/across soil fertility gradients is thought to involve trade-offs between the nutrient and carbon economies of plants. Little is known, however, about how these two types of trade-off interact. We asked if the growth versus shade tolerance trade-off in Australian subtropical rainforest is influenced by soil phosphorus (P) availability, and if similar trade-offs occur on P-rich basalt and low-P rhyolite.

We measured growth of juveniles (400-1200 mm tall) of 15 common tree species across a wide range of light intensity in an Australian subtropical rainforest. Nine common species were measured on the basaltic soil and seven on the rhyolitic soil; one species occurred on both soils. We used hemispherical photographs to quantify light environments above each plant. We then used relationships of growth with light to compare growth of each species at 3, 6, 12, and 20% light availability, and to calculate two measures of species’ light requirements: (a) the light compensation point (the light level at which stem growth averages zero) and (b) the minimum light requirement (the bottom 5% of the range of light environments occupied by each species).

Growth in 3 and 6% light was negatively related to minimum light requirements, but positively related at 20% light. Similar growth versus shade tolerance trade-offs were found among species adapted to the two different substrates. However, the species growing on P-rich basalt encompassed a wider range of light compensation points and growth rates than species growing on low-P rhyolite.

Our results suggest that differential adaptation to soil P availability has little effect on the relationship between shade tolerance and maximum growth rates. However, they do suggest an effect on functional diversity: both the fastest-growing species and the most shade-tolerant species are limited to P-rich soils.

Image caption: Photo provided by authors.
You can read the article in full here.

 

Cold hardiness does not limit range shifts of Mediterranean pines to Central and Western Europe

Christoph Bachofen, Thomas Wohlgemuth, Jaboury Ghazoul and Barbara MoserPinus nigra seedlings growing in the common garden in the Central Alps. Photograph by Christoph Bachofen.

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Mediterranean tree species are adapted to long dry periods during summer, thus they might be well adapted to drought spells, which are projected to increase in Central Europe if climatic conditions become warmer and dryer. Frost, on the other hand, is an important factor limiting the distribution ranges of many tree species. It causes damage to buds and needles during winter and spring. Species distribution models predicting latitudinal range shifts might underestimate the risk from freezing damage, because they rely on average climate data and knowledge of the loss of cold hardiness from winter to spring, called dehardening, is sparse for many tree species.

We estimated the vulnerability of Mediterranean pines to winter and spring frost, and thus their potential to migrate northwards, by comparing the cold hardiness of Mediterranean populations of Pinus sylvestris (Scots pine), Pinus nigra (black pine) and Pinus halepensis (Aleppo pine) to Central Alpine populations of P. sylvestris. Seedlings were grown in a common garden in a cold Central Alpine valley. We artificially froze needles of every species and population at several temperatures on seven dates between February and July 2013. Cold hardiness was determined by estimating the temperature at which the majority of the needles were injured. Needle injury was measured in terms of the amount of electrolytes leaking from the ruptured needle cells.

We found no difference between the cold hardiness of Mediterranean P. sylvestris and P. nigra and Central Alpine P. sylvestris. The cold hardiness was not related to the temperature at the seed origin of the populations. All populations of P. sylvestris and P. nigra maintained extremely wide safety margins against frost, which exceed that of deciduous trees considerably. P. halepensis, on the other hand, exhibited a very narrow safety margin until late spring and its cold hardiness was in the range of temperatures that regularly recur in Central Europe in winter.

Our study shows that Mediterranean P. sylvestris and P. nigra populations are equally well adapted to the late winters and spring frosts of Central Europe as P. sylvestris from the Central Alps. P. halepensis might be resistant to winter temperatures occurring in the Atlantic region of Europe but not to current frost events in Central Europe.

Image caption: Pinus nigra seedlings growing in the common garden in the Central Alps. Photograph by Christoph Bachofen.
You can read the article in full here.

 

Environmental cue to germinate in gaps is closely associated with seed sizes

Qingqing Xia, Mariko Ando and Kenji SeiwaSeed germination experiment in a plant growth chamber in which we provided a R: FR ratio by stick-type light-emitting diode lamps.

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It is well known that seeds of pioneer species use either temperature fluctuations or spectral composition of light as gap detection signals. The relative importance of these two signals, however, remains unknown due to the lack of germination experiments testing the interactive effects of the different signals. We hypothesized that the relative importance of these two factors differs among species with different seed sizes, because the environmental signals may change with soil depth in different manner.

We monitored changes in these environmental signals at different soil and litter depths in forest gaps and under adjacent forest understorey. We also conducted a seed germination experiment in darkness and under red to far-red (R: FR) light ratios of 0.1, 0.4, and 1.0 under fluctuating (30/10 °C day/night) and constant (20 °C) temperatures using 10 pioneer tree species with different seed sizes.

In forest gaps, light is a germination cue that is detectable only at the soil surface or immediately below it when litter is absent, whereas temperature signals can be detected in deeper soil. The proportion of seeds germinating in small-seeded species (seed mass ≤1.05 mg) was strongly promoted by higher R: FR ratios, thereby ensuring germination of seeds buried close to the soil or litter surface. In contrast, percent germination of large-seeded species (seed mass ≥200 mg) was strongly facilitated by temperature fluctuations, ensuring germination of seeds even if buried in deeper soil and litter. In three medium-seeded species (2.84–9.50 mg), interactive effects of the two signals were observed.

Our results suggest that in temperate pioneer trees, differences in seed size across species were associated with differences in the relative importance of light vs. temperature regimes as germination cues for gap detection.

Image caption: Seed germination experiment in a plant growth chamber in which we provided a R: FR ratio by stick-type light-emitting diode lamps.
You can read the article in full here.

 

Do non-native plants have the same traits at home? A comparison in France and New York

J. Mason Heberling ,Thomas Kichey, Guillaume Decocq, and Jason D. FridleyCommon buckthorn on the forest edge in the native France (left) and invasive New York, USA (right). Photo by J.M. Heberling.

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Non-native species become invasive when they actively spread in their introduced range. Trait comparisons between invasive and native species that occur in the same habitat have provided important explanations for how certain non-native species are so successful in their new range. However, it is unclear if these invasive species function similarly in their native range. In other words, do “invasive traits” arise after introduction or do some invasive species also display these traits in their native range?

We compared leaf traits associated with plant function of two important forest invaders in their native (home) and introduced (invaded) ranges: black cherry, a tree native to the Eastern North America but invasive in Europe, and common buckthorn, a shrub native to Europe but invasive in Eastern North America. This transatlantic comparison was unique in that where one species is native the other is invasive, and vice-versa. Because the two species occur in the same regions, we could better control for the potential effect of regional conditions like climate to understand the effect of whether the species is invasive to the region.

We found striking differences in leaf traits associated with plant strategy between native and invaded ranges for both species. Black cherry had similar rates of photosynthesis in the forests of native New York and invasive France, but leaves in France contained more carbon. Trait differences between home and invaded regions were more pronounced for common buckthorn, with 50-60% higher rates of photosynthesis in the invaded region (New York) compared to native France. Buckthorn leaves in New York also tended to have greater leaf nitrogen costs (an important nutrient for photosynthesis) and resorbed proportionately less of this nitrogen in autumn prior to dropping leaves. Autumn leaf nitrogen concentrations were 69% lower in France than New York. This trait might explain how buckthorn is able to drop its leaves later than other species in the invaded range.

Overall, our study shows that traits, which together form a plant’s resource-use strategy, can be different between native and non-native ranges.

Image caption: Common buckthorn on the forest edge in the native France (left) and invasive New York, USA (right). Photo by J.M. Heberling.
You can read the article in full here.

Plant-animal interactions

Dung beetles reduce drought stress in plants without increasing plant susceptibility to an aboveground herbivore

Scott N. Johnson, Goran Lopaticki, Kirk Barnett, Sarah L. Facey, Jeff R. Powell and Susan E. Hartley Rain exclusion shelters at the DRI-GRASS research platform.

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It’s reckoned that insects provide well in excess of USD $500 billion of ecosystem services to mankind every year in the form of pollination and pest control. Some of the most important providers, however, have the less glamorous role of consuming animal faeces – the dung beetles. There are over 6,000 species of dung beetle living on all continents except Antarctica. These beetles provide ecological functions and services by virtue of their physical manipulation of the ecosystem, making them miniature ecosystem engineers. In addition to consuming animal dung, these engineers disperse and incorporate it into the soil via burrowing activity. This drives a number of ecological processes including nutrient cycling, soil aeration, seed burial and parasite suppression. This is estimated to contribute an amazing USD $380 million in ecosystem services to the US cattle industry alone. We were interested in whether these ecosystem services might help mitigate the negative impacts of climate change, particularly altered rainfall patterns, on plant growth and productivity.

Using rain exclusion shelters in SE Australia, we tested how dung beetles (Bubas bison) might alleviate the negative impacts of drought on plants (Brassica oleracea) by enhancing soil water retention. Provisioning plants with resources, however, might make them more nutritious for herbivores and potentially cancel out any benefits that dung beetles conferred, so we also tested whether plant suitability to a herbivorous pest (Plutella xylostella) changed when dung beetles were present. We found that dung beetles increased soil water retention by 10% and increased plant growth by almost three fold under drought conditions. Dung beetles also allowed plants to capture more nutrients such as nitrogen and carbon. Contrary to our predictions, however, dung beetles did not make the plants more susceptible to the herbivore, potentially because they increased nutrient content but not the concentration in leaves. These results point to a potential beneficial role for insect ecosystem engineers in climate change adaptation and crop protection.

Image caption: Rain exclusion shelters at the DRI-GRASS research platform.
You can read the article in full here.

 

Impacts of toxic nectar on three pollinators

Erin Jo Tiedeken, Paul A. Egan, Philip C. Stevenson, Geraldine A. Wright, Mark J. F. Brown, Eileen F. Power, Iain Farrell, Sharon M. Matthews, and Jane C. Stout Invasive Rhododendron ponticum.

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Pollinator decline is a serious concern worldwide; pollinators are important for global food production, and they are also essential in maintaining the diversity of flowering plants on our planet. One cause of pollinator declines is thought to be the spread of highly abundant and ecologically damaging species beyond their native ranges (invasive alien species). Nevertheless, researchers still do not understand the direct impacts that invasive plants have on pollinators.

In this study, we show that an invasive plant in the United Kingdom and Ireland, Rhododendron ponticum, has very different effects on three economically and ecologically important pollinating bee species. Rhododendron nectar was toxic to native Irish honeybees, killing individuals within hours of consumption. The nectar also had negative impacts on the foraging behaviour of a native Irish solitary bee. The solitary bees became paralyzed after feeding on Rhododendron nectar, and ate less food than bees fed a control nectar. In contrast, the native buff-tailed bumblebee was able to consume the nectar with no negative responses, even when the bumblebee was weakened by lack of food or parasite infection. Invasive Rhododendron may therefore provide an important novel nectar resource for this bumblebee species, especially in the early spring when bumblebee queens are establishing their colonies.

Our study shows that the toxicity of Rhododendron nectar is due to the presence of a neurotoxin that humans are also susceptible to, called grayanotoxin I. Many plant species contain such “nectar toxins,” chemicals that are usually associated with defence against foliar herbivores. Our paper demonstrates that invasive plants may differentially impact pollinators, providing new food resources only to those that can tolerate their nectar toxins. In addition, this work demonstrates the importance of comparing the susceptibility of multiple species to natural and synthetic chemicals before making conclusions about the impact of substances on pollinators as a whole.

Image caption: Invasive Rhododendron ponticum.
You can read the article in full here here.

Animal physiological ecology

Temperature-dependence of fish performance in the wild: links with species biogeography and physiological thermal tolerance

Nicholas L. Payne, James A. Smith, Dylan E. van der Meulen, Matthew D. Taylor, Yuuki Y. Watanabe, Akinori Takahashi, Teagan A. Marzullo, Charles A. Gray, Gwenael Cadiou & Iain M. SuthersSand whiting Sillago ciliata. Image Credit: Nick Dawkins.

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It is well known that temperature has a strong influence on the performance, growth, and fitness of ectothermic (“cold-blooded”) animals. However most of our understanding comes from studies of animals in captive laboratory settings. Unlike in the laboratory, ectotherms in the wild need to balance the influence of temperature on their physiology (e.g. rates of metabolism or enzyme reactions) with a need to eat, avoid predation, compete and also reproduce, but we have little understanding of how temperature influences performance of ectotherms in their natural habitats.

We measured body activity and growth rates in the wild for fishes from nine species, and across a broad range of temperatures. Temperature had a strong influence on fish performance in the wild, and in terms of both body activity and growth rates, the more-tropical species performed best in the wild at higher temperatures than did species with more-temperate distributions (tropical species had higher “optimum temperatures”). The tropical species also tended to have optimal temperatures that were closer to the highest temperatures they experience throughout their geographical distributions than did temperate species; temperate species generally maintained a larger “buffer” between their optimum temperatures and the warmest temperatures encountered in their natural range.

We were also interested to know whether the trends seen in our wild data reflect trends seen in earlier physiological studies of how temperature influences performance in captive fishes. We compiled published, laboratory-derived data on fish aerobic scope – the difference between minimum and maximum metabolic rates – and found that the buffer which wild fish maintain (between their optimum performance temperatures in the wild and the highest temperatures in their range) is very similar to the difference between the optimum temperature for aerobic scope and the critically high temperature where aerobic scope plummets to zero in the laboratory.

The combination of data from the field and laboratory highlights the major influence of temperature on ectotherm performance, and shows how closely the influence of temperature on physiology (in this case aerobic scope) seems to translate into patterns of performance in the wild. Interestingly, these data also suggest that fish species tend to perform best in the wild near the highest temperatures they encounter in their range, while maintaining a “safety margin” from the negative effects of critically high temperatures.

Image caption: Sand whiting Sillago ciliata. Image Credit: Nick Dawkins.
You can read the article in full here.

 

Old birds become worn and rusty too

Katherine A. Herborn, Francis Daunt, Britt J. Heidinger, Hanna M. V. Granroth-Wilding, Sarah J. Burthe, Mark A. Newell and Pat MonaghanFamily of Isle of May shags, Phalacrocorx aristotelis. ©Lucie Bernardova.

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While we know that our own bodies deteriorate as we get older, relatively little is known about these processes in wild animal populations. Much of what we know about aging in other species comes from research on species with relatively short lifespans, such as insects and rodents, which can be studied from birth to death in laboratories. To determine whether the same patterns of aging occur in long lived organisms requires long term programmes and long scientific careers. Moreover, understanding aging under natural conditions, instead of in the relatively homogenous and safe laboratory environment, presents the additional challenge of finding the same animal at different stages of its life in the wild. One reason why individuals deteriorate with age is thought to be akin to rusting – that is accumulated oxidative damage to tissues. The term ‘oxidative stress’ describes a state where oxidising molecules, which are mostly a natural by-product of metabolism, exceed the body’s level of antioxidant defences, and thus are free to react with and damage body tissue. We examined age-related changes in oxidative stress exposure in the Isle of May population of a long-lived seabird, the European Shag (Phalacrocorax aristotelis). Chicks were given unique coloured and lettered leg rings, allowing them to be recognised throughout their lives. Over three consecutive breeding seasons, we collected tiny blood samples from individuals aged from 2 to 22 years at the start of the study. Individuals of all ages showed an increase in oxidative stress exposure from one year to the next, and those with the highest levels were more likely to die. This is consistent with the expectation that older individuals will invest less energy and resources into self-maintenance in favour of more investment into reproduction, as a last ditch attempt at passing on their genes. Our study, therefore, provides a rare insight into the process of aging in a long-lived species; they become rusty much like ourselves.

Image caption: Family of Isle of May shags, Phalacrocorx aristotelis. ©Lucie Bernardova.
You can read the article in full here.

 

Food as fuel: How food protein-carbohydrate content affects resting metabolic rates

Rebecca M. Clark, Anthony J. Zera, and Spencer T. BehmerFemale cricket housed in a flow-through respirometry chamber used to measure carbon dioxide production and oxygen consumption.  Photo by S.T. Behmer.

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Metabolic rate is a fundamental physiological characteristic of animals that summarizes overall energy usage by an organism. Because of its central role in organismal physiology, metabolic rate is widely thought to be influenced by external and internal factors, especially food nutrient content and physiological state (e.g. reproductive status). However, despite decades of study in the context of nutritional ecology and life-history evolution, the effects of food nutrient content and animal reproductive status on resting metabolic rates are poorly understood.

We tested how the balance and concentration of protein and carbohydrate in food affected resting metabolic rate in females of the sand cricket, Gryllus firmus. Females of this species occur in two physiologically distinct forms (morphs) that specialize in either flight ability or egg production. Because these forms differ dramatically in many aspects of fat and amino acid metabolism related to production of fat flight fuel and eggs, we also expected them to differ in metabolic rate. Surprisingly, we found that the dramatic differences in organismal biochemistry did not lead to differences in resting metabolic rates between the morphs. Likewise, resting metabolism was similar across diets, even though the diets had different protein-carbohydrate profiles. The maintenance of constant resting metabolic rate on different diets occurred because crickets shifted the nutrients that they used as metabolic “fuel,” to compensate for changes in the amount and ratio of protein and carbohydrate in their diet.

Therefore, counter to expectations, individuals can experience dramatic variation in nutrient input and have vastly different physiological characteristics, without showing any signs of these major distinctions at the level of whole-body resting metabolic rate. Conversely, the absence of differences among individuals in resting metabolic rate does not necessarily mean that those individuals do not differ dramatically in underlying aspects of biochemical function. Physiological studies need to be undertaken both at the whole-organism and biochemical levels to identify adaptive biochemical differences among individuals and to determine the extent to which these differences give rise to differences in overall energy usage.

Image caption: Female cricket housed in a flow-through respirometry chamber used to measure carbon dioxide production and oxygen consumption. Photo by S.T. Behmer.
You can read the article in full here.

 

Visual ecology of Eulemur suggests a cathemeral origin for the primate cone opsin polymorphism

Kim Valenta, Melissa Edwards, Radoniaina R. Rafaliarison, Steig E. Johnson, Sheila M. Holmes, Kevin A. Brown, Nathaniel J. Dominy, Shawn M. Lehman, Esteban J. Parra, Amanda D. Melin A brown lemur (Eulemur fulvus) searches for fruits under daylight conditions in Ankarafantsika National Park, Madagascar. Photo credit: Travis Steffens.

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Unlike most primates, which are predominantly active during either the day or night, lemurs in the genus Eulemur are active across the 24-hour daily cycle. Although debated, recent evidence suggests that this activity pattern has a long evolutionary history for these lemurs, and was possessed by their ancestors. The impact of nighttime vs. daytime activity on the evolution of color vision in primates is actively debated and we explore the visual ecology of lemurs that are active at both times to shed new light on this debate. We studied three groups of wild brown lemurs (Eulemur fulvus) in Ankarafantsika National Park, Madagascar and collected stool samples for DNA analysis to study the opsin genes underlying color vision. We measured the color and brightness of dietary fruits and modeled the conspicuousness of food objects to different color vision types under daylight, twilight, and moonlight conditions. We found the color vision of E. fulvus to be routinely dichromatic – all males and females had the same color vision, consisting of two color channels. Our models suggest that dichromacy is well-suited to the foraging ecology of this species. The color vision of E. fulvus differs from its close relative E. flavifrons, for which polymorphic trichromacy – the addition of a third (red-green) color channel in some females - has been reported. We suggest that ecological differences between species of Eulemur could reveal thresholds for the origins of polymorphic trichromacy, which preceded the evolution of routine trichromatic vision in humans and other primates.

Image caption: A brown lemur (Eulemur fulvus) searches for fruits under daylight conditions in Ankarafantsika National Park, Madagascar. Photo credit: Travis Steffens.
You can read the article in full here.

Behavioural ecology

Effects of neonatal size on maturity and escape performance in the Trinidadian guppy

Terry Dial, David Reznick and Elizabeth BrainerdImage provided by authors.

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Newborn offspring are always smaller than the parent, but not all offspring are born the same size or same level of maturity, so what factors ultimately control the evolution of offspring size? Parents balance the tradeoff between offspring size and offspring number, and the optimal balance depends largely on the environment.

In response to high predation pressure by large predatory fish, Trinidadian guppies produce lots of small babies, flooding their environment with numbers. Above waterfall barriers, in environments with low or no predation, guppies produce fewer, larger babies.

To avoid a predator, fish will initiate an escape start by first bending their body into a C-shape and then undulating out of it, away from the threat. In other fish studied, larger individuals are known to produce higher performance escape starts. Thus, it is somewhat paradoxical that an adaptation to living with predators is to produce babies that are born with an inherent size disadvantage, but are they?

Here we measure escape performance of newborn guppies from five populations adapted either to low predation, high predation, or extreme high predation environments. We also measured detailed morphology, both external and internal, to assess whether these offspring possess different body proportions or levels of maturity. We find that those fish responding maximally to our stimulus perform at the upper limit for their size, and that both size and maturity influence this escape performance limit.

The smallest guppies are extremely slow at performing the escape start, even for their size, and these smallest offspring are also less developmentally mature compared with their larger counterparts. Within the Trinidadian guppy, it appears that both size and maturity tradeoff with number of offspring, and that offspring abundance outweighs performance in environments with the highest predation pressure.

Image caption: Image provided by authors.
You can read the article in full here.

 

Predation, food, and male-male competition drive natural variation in lizard tail autotomy

Chi-Yun Kuo and Duncan J. IrschickSide-blotched lizard couple sharing a burrow. Photo credit: Chi-Yun Kuo.

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Autotomy, or the voluntary shedding of body parts, is a behavior many animals (> 100 vertebrate and invertebrate families) use to survive predation. In some animals the detached body parts would continue moving to divert the attention of the predators away from the escaping animal. Autotomy is normally triggered by a force exerted on the discardable body part. In most cases the force comes from a predator but can sometimes be the result of male-male combats. Despite its benefit in enhancing the chance of survival in the field, autotomy imposes numerous short- and long-term costs, such as risk of infection, lower locomotor performance, lower mating success, and ultimately long-term survival. High costs of autotomy imply that selection should not take the use of this behavior lightly, and how easily autotomy occurs should reflect the underlying cost-benefit dynamics. Indeed, how easy it is to induce autotomy (i.e. the propensity for autotomy) exhibits remarkable variation among populations. In this study, we combined model simulations and field data to explicitly test the hypothesis that the ecological environment drives the variation in autotomy among populations. We first built a simple model to examine the roles of three major ecological factors: predation, food abundance, and male-male competition. Our predictions for the three factors are as follows: high predation and an abundance of food should favor high propensities for autotomy (i.e. easier to induce), as the former situation would increase the benefit of autotomy while the latter makes autotomy less expensive. On the contrary, more male-male fighting should favor lower propensities for autotomy because it is undesirable to lose body parts under non-life threatening situations. Simulation results confirmed all our predictions above. We then collected data on predation, food abundance, the intensity of male-male competition, and the propensity for tail autotomy from five side-blotched lizard populations in western U.S. With the ecological information, our model was able to predict how those five populations should vary in the propensity for tail autotomy. Again, our model successfully predicted the pattern of variation observed in the field, thereby providing further evidence that predation, food abundance, and male-male competition jointly drive natural variation in autotomy among populations.

Image caption: Side-blotched lizard couple sharing a burrow. Photo credit: Chi-Yun Kuo.
You can read the article in full here.

 

Short-term rainfall, not temperature, controls lizard microhabitat use in a piñon-juniper woodland

Mason J Ryan, Ian M Latella, J. Tomasz Giermakowski, Howard Snell, Steven Poe, Robert E Pangle, Nathan Gehres, William T Pockman & Nate G McDowellImage provided by authors.

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As climate change increases temperature globally and alters regional rainfall, the activity and foraging behavior of cold-blooded animals (ectotherms) like lizards must also change if individuals are to grow and reproduce. Lizards respond to higher temperatures by decreasing activity and reducing foraging time, particularly in sunlit locations, to limit heat gain. While these behavioral changes at higher temperature are linked to population declines, little is known about how lizards will respond to decreases in rainfall in arid environments predicted to accompany warming. Moreover, tests of these responses are difficult in natural environments because experimental manipulations of temperature and rainfall are uncommon.

To examine how wild lizards respond to changing temperature and rainfall, we measured lizard responses in a piñon-juniper woodland in New Mexico where rainfall and temperature were manipulated on 40 x 40 m plots assigned to one of four treatments: Drought imposed by plastic troughs diverting 45% of natural rainfall, Warming plots with inverted plastic troughs that raised temperatures without diverting rainfall, Irrigation plots with sprinklers that simulated rainfall, and unmanipulated Control plots. In the context of these treatments, we observed lizards and recorded their activity and use of shade or sun microhabitats. This design allowed us to determine how rainfall and/or temperature influenced lizard activity and decisions about foraging in sun vs. the shade of trees.

Contrary to recent studies, we found that rainfall, not temperature, strongly influenced lizard behavior. During dry periods, lizards foraged almost exclusively in shade under trees, whereas lizards foraged in sunny areas across the landscape following natural or simulated rainfall events. Temperature did not influence lizard behavior, even in the covered plots with the warmest temperatures, a surprising result considering the wealth of research showing lizard temperature sensitivity. We conclude that our study lizard is more sensitive to moisture and relies on tree shade as a refuge during dry periods. The long-term drying trends that are increasing tree mortality in piñon-juniper woodlands may decrease the availability of this critical lizard microhabitat.

Image caption: Image provided by authors.
You can read the article in full here.

Community ecology

The importance of biotic interactions for the prediction of macroinvertebrate communities under multiple stressors

Nele Schuwirth, Anne Dietzel and Peter ReichertMayfly with eggs, taken by Nele Schuwirth.

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In this study we tested a computer model to predict the occurrence of macroinvertebrates in streams. Macroinvertebrates are aquatic organisms that live on the river bed or in the sediment, like insect larvae, snails, worms, or crustaceans. They are very diverse and have different environmental requirements, e.g. regarding temperature, flow velocity, substrate types, water quality, and they are specialized on different food sources. Because their community composition depends on the environmental conditions, they can be used to assess the ecological state of rivers and the influence of human impacts, like water pollution, channelization, or modifications of the flow regime. For decision support in river management it is important to predict the influence of different management activities on the ecological state of the rivers. To this end, predictive models can be useful tools.

Based on existing knowledge about the requirements of different macroinvertebrate taxa and some basic principles, like mass conservation or the scaling of vital rates with body-size and temperature, we constructed the process based model called "Streambugs". The model aims to predict which species, genera or families are expected to occur at which sites. We used existing monitoring data from 36 sites in the Glatt catchment at the Swiss Plateau to compare model predictions with observations. Even without fitting the model parameters (factors that influence growth, respiration and death processes) and just relying on prior knowledge about these parameters, for 79% of the taxa at the 36 sites the difference between the observed and predicted frequency of occurrence is less than 50%. This is considerably better (+18%) than a random model that assigns a 50% chance to observe or not observe each taxon at each site and each sampling event. By adjusting factors that increase or decrease the growth rates of the different organisms, we can increase model compliance with data. Furthermore, we tested which properties of the organisms contributed most to the predictive power of the model. In this catchment, sensitivity to organic toxic substances as well as feeding-types were most important for making good predictions. These results highlight that biotic interactions between the organisms (competition for food and predator-prey interactions) should be taken into account when trying to predict the occurrence of aquatic organisms in streams.

Image caption: Mayfly with eggs, taken by Nele Schuwirth.
You can read the article in full here.

 

How do precipitation gradient and evolutionary history shape the variations in leaf and root traits in the Inner Mongolia grassland?

Junhui Cheng, Pengfei Chu, Dima Chen and Yongfei BaiRoot systems of six grasses widely distributed in the Inner Mongolia grassland.

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The attributes of leaves and roots are fundamental for understanding different strategies that plants use to acquire resources, like water, soil nutrients, and light, in different environmental conditions. This is important because these resource acquisition strategies are essential for species coexistence, community assembly and functioning of terrestrial ecosystems. Species with less dry matter investment per leaf area and root length have high growth rate but short life span, indicating a resource acquisitive strategy. In contrast, species with high dry matter investment per leaf area and root length have low growth rate but long life span, suggesting a resource conservative strategy. It has been assumed that variation in environmental factors (e.g. precipitation and temperature) and evolutionary history (species divergence time on the evolutionary tree) shape both leaf and root traits. The branching architecture of fine roots also affects the functional role of living roots, such as acquisition and transport of water and nutrients. However, few studies have examined the effects of evolutionary history and environmental gradients on species leaf and root traits, or considered how plants are able to access increasingly scarce resources like water and nutrients as climate shifts from relative moist to very arid?

In this study, we examine how leaf and root traits vary across 55 species and 21 plant communities along a 2,000-km transect in the Inner Mongolia grassland, part of the largest contiguous grassland in the world, the Eurasia steppe. Our results suggest that acquisition of soil resources, such as water and nutrients, is a fundamental determinant of plant dry mass investment per root length in arid and semiarid grasslands. Across the transect, species that evolved relatively late tended to have high dry matter investment per leaf area and root length for the first root branching order, and were distributed in dry and infertile habitats, while earlier-evolving species exhibited low dry matter investment per leaf area and root length and were found in wet and fertile habitats. These findings provide new insights for predicting the response of species and ecosystems to changes in temperature and precipitation in arid and semiarid grasslands.

Image caption: Root systems of six grasses widely distributed in the Inner Mongolia grassland.
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Functional replacement across species pools of vertebrate scavengers separated at a continental scale maintains an ecosystem function

Chantal M. Huijbers, Thomas A. Schlacher, Rosemary R. McVeigh, David S. Schoeman, Andrew D. Olds, Marion B. Brown, Kasun B. Ekanayake, Michael A. Weston and Rod M. Connolly Removal of fish carcasses from ocean beaches, a key ecological function, is maintained across a continental scale via functional species replacement: scavenger assemblages on tropical beaches were dominated by raptors, such as white-bellied sea eagles (left image), and substantially different from temperate scavenger assemblages, which were dominated by red foxes (right image). Photographs taken while scavengers were actively removing beach carrion during the experiments. Credits: C. Huijbers.

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The composition of the total variety of species available to colonise a particular site (the ‘species pool’), and those that actually occur together (the local assemblage), often show large geographical variation, reflected in distinct ‘faunas’ and ‘bio-regions’ across the globe. Whilst such structural differences are often prominent, much less is known about whether these geographic patterns in species identity change the functioning of ecosystems.

Scavenging, the consumption of animal carcasses, is an important ecological function. We tested how differences in the composition of local scavenger assemblages affect the removal rates of carrion (dead fish) from sandy beaches. We deployed fish carcasses on beaches in tropical north Australia and temperate south Australia and used motion-triggered cameras to monitor which animals scavenge on the carcasses.

Tropical assemblages of vertebrate beach scavengers were dominated by raptors such as brahminy kites and white-bellied sea eagles, while carrion on temperate beaches was mostly removed by invasive red foxes. Despite the distinct differences in terms of which species make up the scavenger assemblages, the rates at which carrion was removed from beaches was similar between regions separated by thousands of kilometres. This indicates that two very distinct species assemblages can maintain a pivotal ecological process via functional replacement of species.

Image caption: Removal of fish carcasses from ocean beaches, a key ecological function, is maintained across a continental scale via functional species replacement: scavenger assemblages on tropical beaches were dominated by raptors, such as white-bellied sea eagles (left image), and substantially different from temperate scavenger assemblages, which were dominated by red foxes (right image). Photographs taken while scavengers were actively removing beach carrion during the experiments. Credits: C. Huijbers.
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Re-growing a tropical dry forest: functional plant trait composition and community assembly during succession

Vanessa Buzzard, Catherine M. Hulshof, Trevor Birt, Cyrille Violle and Brian J. EnquistRecently disturbed TDF in Sector Santa Rosa of Area de Conservación Guanacaste (ACG) in northwestern Costa Rica. Photo credited to Catherine Hulshof.

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Most of the world’s remaining tropical forests have experienced some degree of disturbance. Tropical dry forests (TDFs), which are characterized by seasonal drought, currently occupy 42% of all forested tropical regions throughout the world but today less than 2% of TDFs throughout Central America remain undisturbed. The primary conversion of this forest type is a result of a long history of human land use. In order to restore these tropical ecosystems, ecological studies are needed to help understand how the structure and function of these forests change over time.

Ecological theory suggests that the environmental conditions following disturbance are stressful. Therefore, directly following a disturbance, communities are likely to be characterized by drier and more variable soil moisture, higher light levels, increased temperatures, and lower relative humidity acting as a filter where only a few species can successfully establish. Over time, as environmental conditions improve, more species establish and begin to compete with one another for resources resulting in greater differences between species. This shift in resource availability and turnover in species composition through time has been the primary focus of successional ecology for many years, resulting in little understanding of the change in function over time. Therefore, in this study we take a more mechanistic approach to assess community function over time by measuring physiological and chemical traits of leaves that are related to the success of an individual (functional traits) for woody plants within 14 plots that have varying times since disturbance.

When we compare species composition and community function, we find that older TDF communities differed significantly from younger forests in species composition, above ground biomass and functional traits. The observed trait shifts appear to be primarily determined by a concomitant shift in resource availability, e.g., water availability (reflected in increased soil moisture) and light availability. Further, early stages of succession were uniformly characterized by traits related to strategies important for avoiding water loss, whereas in later successional stages traits reflected increased water and nutrient availability. Interestingly, in contrast to expectations, functional trait variation did not generally change through succession. Our results suggest that regenerating TDFs are resilient and can be restored within a human lifetime.

Image caption: Recently disturbed TDF in Sector Santa Rosa of Area de Conservación Guanacaste (ACG) in northwestern Costa Rica. Photo credited to Catherine Hulshof.
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Liverworts to the rescue: an investigation of their efficacy as mycorrhizal inoculum for vascular plants

Jill Kowal, Silvia Pressel, Jeffrey G. Duckett, and Martin I. Bidartondo Septate hyphae emanating from a microscopic leafy liverwort rhizoid following resynthesis with the ericoid mycorrhizal fungus isolate.

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Healthy plant life aboveground is largely dependent on the function of belowground fungal communities. Mycorrhizal fungi are ubiquitous in the soil, forming mutualistic plant-fungal interactions in all terrestrial ecosystems. Mycorrhizal fungi are not transmitted directly from parent to offspring plants, so mycorrhizal mutualisms must form de novo when plants establish from seed.

A widespread mycorrhiza-forming fungus (Pezoloma ericae (D.J. Read) Baral) associates with plants in the order Ericales and also forms mutualistic associations with several families of liverworts, many of which are also widespread throughout the world. The ecological significance of this ‘shared’ mycorrhizal partnership remains largely unknown. The Ericales number approximately 8,000 species and include familiar plants such as heathers, blueberries and cranberries.

We investigated the functional associations among ericaceous plants, liverworts and mycorrhizal fungi in wet lowland heathland dominated by heathers, a top priority habitat for conservation. The research aimed to determine whether pioneering liverwort plants harbouring P. ericae can act as inoculum for the re-establishment of heather plants and can therefore be proposed as a practical application in heathland restoration ecology. The process of becoming mycorrhizal can be limiting to plant establishment in ecosystems poor in nutrients, such as heathlands.

Our molecular analyses confirmed that the liverworts and heather (Erica tetralix and Calluna vulgaris) share the same mycorrhizal fungus, P. ericae. We cultured liverworts from spores, and introduced the P. ericae isolate. Within weeks, the liverworts were colonized by the fungus, as found in nature. These liverworts were then planted together with heathers (both seedlings and cuttings) in field-simulating conditions, to assess the functional role of the colonized liverworts on the heathland plants. Germination, rooting success, plant survival, and growth were measured after several weeks and months.

Our research showed, for the first time through molecular identification, that British species of leafy liverworts harbour a fungus that forms mycorrhizas with vascular plants. We unequivocally demonstrated that these fungal symbionts emanate from leafy liverwort rhizoids and repeatedly colonize roots forming typical "ericoid mycorrhizas" in seedlings and cuttings. Plant establishment is significantly more successful when plants are co-planted with liverworts containing these fungi. Growth is significantly increased as well, but can be initially suppressed – there may be an initial cost to partnering with fungi.

The liverworts tested are adaptable to considerable swings in temperature and moisture levels in nature, and are relatively easy to cultivate and apply for inoculation treatments. We therefore conclude these liverworts are a viable inoculum delivery mechanism for heather establishment, and preferable to a slurry of the fungus isolate or other Ericaceae plants as they are more cost effective and practical on a large scale. We plan to test this inoculum in nature now that we have established its efficacy in our experiments.

Image caption: Septate hyphae emanating from a microscopic leafy liverwort rhizoid following resynthesis with the ericoid mycorrhizal fungus isolate.
You can read the article in full here.

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