Lay Summaries

The summaries below are provided by our authors to help put their research into context for the wider scientific community and the general public. Lay summaries for the current issue are here. You can also find all the previous lay summaries by issue, as well as summaries for articles on Early View, in the lay summaries archive.

Lay summaries for the current issue, which includes our latest Special Feature: The Functional Role of Silicon in Plant Biology.

 

You can also find all the previous lay summaries by issue, as well as summaries for articles on Early View, in the lay summaries archive.

 

 

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.

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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.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

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. LenhartImage provided by authors.

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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: Image provided by authors.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

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.

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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.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

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.

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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.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

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.

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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.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

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.

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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.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

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.

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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.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

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.

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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.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

The Ecology of De-Extinction

De-extinction and evolution

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

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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.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

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.

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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.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

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).

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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).
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

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).

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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).
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

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.

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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.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

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.

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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.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version 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.

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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.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version 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.

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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.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Stress hormones may help handicapped moms produce young

James W. Rivers, Gretchen N. Newberry, Carl J. Schwarz and Daniel R. ArdiaPhoto provided by authors.

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Stress hormones are typically thought of as being bad for one’s health, but they can be beneficial to individuals over short-term periods of high energetic demand. In this study, we evaluated whether female violet-green swallows, small insect-eating birds found throughout western North America, had altered stress hormone concentrations while undergoing unplanned energetic challenges when rearing young. To test this idea, we experimentally removed a small number of wing feathers at two different intensities (low and high) in some individuals, whereas other individuals were handled in the same manner but had no feathers removed. We measured stress hormone concentrations at two points during the breeding season when females were feeding their young: immediately prior to feather removal, and 10 days later. We also assessed whether females in the three groups varied in how often they fed their offspring, as well as the quality and quantity of young that were raised.

Females in the three groups were initially similar in their body size and in their baseline stress hormone concentrations. However, females experiencing feather removal were found to have much greater increases in baseline stress hormones, and the amount of stress hormones was positively linked to the degree of feather removal. Despite this, females in both feather-removal groups were able to maintain feeding rates at levels similar to control females, and they produced a similar number of young. Offspring from mothers in the different groups did, however, have different levels of stress hormones, the reason for which remains unclear. Overall, this study suggests that energetic challenges are associated with increases in stress hormones, and such increases appear to allow female swallows to maintain feeding rates at a level typical of control females and produce a similar number of offspring. Thus, stress hormones may provide individuals with a way of ramping up their parental effort when they encounter unexpected energetic challenges, so they can produce the same number of young they would have done during a normal breeding season.

Image caption: Photo provided by authors.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version 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).

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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).
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version 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.

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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.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version 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).

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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).
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Climate and atmospheric change impacts on sap-feeding herbivores: a mechanistic explanation based on functional groups of primary metabolites

James M. W. Ryalls, Ben D. Moore, Markus Riegler, Lisa M. Bromfield, Aidan A. G. Hall and Scott N. Johnson Magnified pea aphids (Acyrthosiphon pisum) feeding on an experimental lucerne (Medicago sativa) leaf.

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‘Little things that run the world’ is how E.O. Wilson described insects and other invertebrates, but which ‘little things’ will run a future world with higher atmospheric carbon dioxide concentrations and warmer temperatures? We set about answering this for aphids feeding on lucerne and aimed to get at the underlying plant-mediated mechanisms for changes in their performance. We chose aphids because these troublesome insects transmit at least 50% of insect-vectored plant viruses and therefore cause widespread damage to crops worldwide - a troubling prospect considering that we’ll need to feed another 3 billion people by 2050. In addition, they can have disproportionately large impacts on foodwebs and insect community structure simply because they can reproduce so rapidly in response to favourable environmental conditions. Aphids have been repeatedly identified in reviews and meta-analyses as being a net beneficiary of predicted increases in atmospheric carbon dioxide concentrations, yet the exact mechanisms for this aren’t always clear. Our study addresses a missing piece of this jigsaw by investigating the underlying chemical mechanisms for their success and how concurrent climatic factors (elevated air temperature) interact with elevated CO2. We demonstrated that it was a specific group of amino acids that increased and decreased, respectively, under elevated CO2 and temperature, which was directly correlated with aphid performance. This consistent pattern across five plant genotypes explained why aphids benefited from elevated CO2, yet performance declined when elevated temperature was included. Understanding the chemical mechanisms underpinning insect responses to climate and atmospheric change raises the possibility of building resistance into new crop cultivars and gives us some foresight for preventing pest outbreaks and preserving ecosystem functions.

Image caption: Magnified pea aphids (Acyrthosiphon pisum) feeding on an experimental lucerne (Medicago sativa) leaf.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

The honeybee leads the effect of an exotic plant on resident plant-pollinator communities

Ana Montero-Castaño and Montserrat VilàSubsample of the Mediterranean plant –pollinator community studied.

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Exotic plants that depend on pollinators for their reproduction usually become well integrated into the diet of generalist pollinators. This integration can affect the entire recipient plant-pollinator community; for instance, by attracting pollinators, or on the contrary, by stealing pollinators from the recipient communities. Understanding the factors that govern such variable effects is among the fundamental goals in invasion ecology.

Because species traits determine the interaction between plants and pollinators (e.g. size, shape and colour of flowers and body size or tongue length in pollinators), trait similarity among plants or among pollinators might modulate how they affect each other.

We conducted a flower removal experiment to investigate the effects of the exotic legume Hedysarum coronarium on the pollination patterns of a Mediterranean shrubland community. We explored if the number, frequency or identity of interactions were affected by the exotic and whether the effects were influenced by trait similarity. Specifically, we explored the influence of similarity in flower morphology with Hedysarum (i.e., whether natives were also legumes or not). And in the case of pollinators, we explored the influence of belonging to the same functional group (i.e., whether they were also bees or not) as the main pollinator of Hedysarum, the highly competitive honeybee. Other pollinators were flies and beetles.

Hedysarum was well integrated into the diet of 15 generalist pollinators. Such integration did not affect the pollination of native plants (irrespective of their flower morphology) in terms of number and frequency of interactions, despite a reduction in proportion of honeybee visits. On the other hand, Hedysarum reduced the visitation frequency of bees to both natives and Hedysarum. In addition, pollinators switched the plants they visited (i.e., interaction rewiring) according to the changes in the proportion of honeybee visits. That is, the bigger the change in the proportion of honeybee visits to a given plant, the greater the interaction rewiring.

In conclusion, pollinators respond to plant invasions with a plastic use of floral resources. When the exotic attracts highly competitive pollinators such as the honeybee, plasticity is especially significant for pollinators functionally close to that pollinator, i.e. other bees. The result is an interaction rewiring due to pollinators avoiding competition with the honeybee.

Image caption: Subsample of the Mediterranean plant –pollinator community studied.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

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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)..

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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)
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version 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.

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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.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version 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.

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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.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

Advances and challenges in the study of ecological networks

Species and their interactions

Kristian Trøjelsgaard and Jens M. OlesenA food web consisting of a single top predator (bird), some intermediate species (parasitic wasp, caterpillar, and grasshopper) and a single primary producer (plant). The network is a quick way of illustrating the feeding relationship between the species.

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Virtually no organism lives in isolation, and biotic interactions (e.g. competition, predation, mutualism and parasitism) therefore play an important part in the biodiversity and distribution of species that we see today. One way of analysing complex systems of interacting species is through network analysis, a discipline that has grown considerably in recent decades. Ecological networks consist of nodes (typically species) that are connected because they somehow interact. A good example is food webs where predators are connected to prey, which in turn can be connected to plants, and as such, the food web demonstrates who eats whom. Interestingly, it has turned out that human networks like air transportation networks, the Internet, and sexual relationships between humans have many structural commonalities with the ecological networks we find in nature. For example, most species (or humans) have few interaction partners while a few nodes have disproportionately many interaction partners.

As stated, ecological networks provide a way of capturing whole communities of interacting species in a single analysable entity. The variability that ecological networks exhibit across space and time is likely to teach us how networks of interacting species will respond to e.g. future climate changes. Interestingly, temporal comparisons of ecological networks range from within season to across millions of years, and spatial comparisons have been done within a single km, across regions or even across the globe. Herein we review what such studies have taught us and list potential ways of moving forward.

We emphasize that although networks may look calm on the surface, when compared across space and time, there seems to be much variability underneath. For example, individual species may change with whom they interact, with how many they interact, and also their role in the community. This microscopic (i.e. below the network level) variability deserves further attention, and is likely to add another dimension to network variability.

Image caption: A food web consisting of a single top predator (bird), some intermediate species (parasitic wasp, caterpillar, and grasshopper) and a single primary producer (plant). The network is a quick way of illustrating the feeding relationship between the species.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version 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.

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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.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

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