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.

  • Long-lasting effects from previous winter warming events suggest that an important sub-Arctic moss will be disadvantaged in a future sub-Arctic climate Bjerke et al
  • Joint effects of climate change and parasite infection on host in the wild Bruneaux et al
  • The effect of egg size on hatch time and metabolic rate: theoretical and empirical insights on developing insect embryos Maino et al
  • Positive species diversity and above-ground biomass relationships are ubiquitous across forest strata despite interference from overstorey trees Zhang et al
  • Do thermoregulatory costs limit altitude distributions of Andean forest birds? Londoño et al
  • The plant you choose to make your home isn't always the one that protects you best Ali & Agrawal
  • Movement correlates of lizards' dorsal pigmentation patterns Halperin et al
  • Testosterone and the cloacal microbiome in a free-living bird Escallón et al
  • Host phenology and potential saprotrophism of ectomycorrhizal fungi in the boreal forest Hupperts et al
  • New ranking algorithm can identify overall pattern from incomplete surveys, providing critical insight into complex problems Swain et al
  • Fire impacts on soil organisms Soong et al
  • Phytopathogens affect plant volatile emissions and the attraction of parasitoid wasps Ponzio et al
  • Linking the respiration of fungal sporocarps with their nitrogen concentration: variation among species, tissues, and guilds Trocha et al
  • Limited flexibility in heat tolerance suggests vulnerability to climate change van Heerwaarden et al
  • Searching for prey in a three-dimensional environment: hierarchical movements enhance foraging success in northern elephant seals Adachi et al
  • Litter microbial and soil faunal communities stimulated in the wake of a volcanic eruption in a semiarid woodland Berenstecher et al
  • Using functional responses to quantify interaction effects among predators Wasserman et al
  • Fertilization changes goldenrod’s defensive response to grasshoppers Burghardt
  • Predator-prey mass ratio revisited: Does preference of relative prey body size depend on individual predator size? Tsai et al
  • How bark properties promote invertebrate diversity in tree logs during early decay Zuo et al
  • Relative importance of soil properties and microbial community for soil functionality Delgado-Baquerizo et al
  • Are dive bottom durations good indicators of fur seal foraging success? Viviant et al
  • Stable isotopes reveal the ecology of tropical butterfly larvae. Van Bergen et al
  • Mycorrhizal and saprotrophic fungal guilds compete for the same organic substrates but affect decomposition differently Bödeker et al
  • Evolutionary history imprinted on species interaction Peralta
  • Neighboring resources can affect the attractiveness of resources occurring in the neighborhood Verschut et al
  • Who interacts with whom? A common framework for identifying linkage rules across different types of interactions Bartomeus et al
  • Energy expenditure of adult green turtles at sea Enstipp et al
  • Author-suggested reviewers: Gender differences and influences on the peer review process at an ecology journal Fox et al
  • Lay summaries for the current issue.

     

    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.

     

     

    Long-lasting effects from previous winter warming events suggest that an important sub-Arctic moss will be disadvantaged in a future sub-Arctic climate

    Jarle W. Bjerke, Stef Bokhorst, Terry V. Callaghan & Gareth K. PhoenixA shoot of splendid feathermoss with fertile organs (sporophytes) protruding from the green shoot segments, which are partly blurred. Photo credit: Jarle W. Bjerke.

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    Understanding the impacts of climate change on ecosystems is complex for many reasons. Firstly, there are many drivers of change and each driver has numerous interacting facets. Secondly, there are practical issues that hinder research, such as difficult species groups and winter research. Here we focus on a moss (an understudied plant group), the winter period (under-represented in field studies) and extreme warming events, that are both difficult to observe and even more difficult to predict. Winter is a period of dormancy for plants of cold environments. However, winter climate is changing, leading to an increasing frequency of warm weather events that temporarily reduce snow cover. These conditions can break dormancy for some plants and expose them to freeze-and-thaw stress. Mosses are a major component of northern lands, yet the longer-term impacts of such winter warming events on mosses remain unknown. Therefore, we undertook a field experiment to simulate these events over three consecutive winters in a sub-Arctic open woodland. The mat-forming splendid feathermoss (Hylocomium splendens), also known as the glittering woodmoss or stairstep moss, was the most abundant moss species at our site, and we studied it during both the experimental years and in the years following these events. This is probably one of the most abundant moss species in the World, and plays important roles such as insulating the ground. We found that the warming events reduced its vitality. Both photosynthesis and shoot growth rates declined considerably and were still much lower than in non-experimental plots even four years after the last warming event. These results suggest that this moss will be disadvantaged in a future sub-Arctic climate where a high frequency of winter warming events may become the norm. More broadly, this suggests the potential for large consequences for northern lands where mosses are often a major component of the vegetation and where the greatest increases in extreme winter events may be expected. This will again have a strong influence on ground temperature and moisture, cycling of nutrients and water, permafrost thaw and ecosystem carbon balance.

    Image caption: A shoot of splendid feathermoss with fertile organs (sporophytes) protruding from the green shoot segments, which are partly blurred. Photo credit: Jarle W. Bjerke.
    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.

     

    Joint effects of climate change and parasite infection on host in the wild

    Matthieu Bruneaux, Marko Visse, Riho Gross, Lilian Pukk, Lauri Saks, Anti VasemägiEcologist at work. Photograph provided by authors.

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    Climate change can affect ecosystems in several ways, through direct temperature effects on organisms (e.g. limiting metabolic capacity at high temperatures) or through indirect effects, such as an increased parasite burden or the introduction of new parasites. These negative effects can interact with potentially dramatic consequences, when high temperatures disrupt the immune function of the host and make it unable to resist a parasite infection, or when the parasite infection compromises the ability of the host to cope with elevated temperatures.

    The physiological effects of parasites have been traditionally evaluated under controlled laboratory conditions. However, much less is known about the effect of emerging parasitic diseases on host performance in nature. We studied wild-caught juveniles of brown trout (Salmo trutta) and measured several physiological and performance traits to evaluate the effect of proliferative kidney disease (PKD), which is caused by the myxozoan parasite Tetracapsuloides bryosalmonae This parasite can result in high mortalities in salmonid species, both in farms and in natural ecosystems, and its range has extended in recent years. To understand how parasite load, metabolic rate and thermal resistance are related to each other in the fish host, we brought our physiological laboratory into the field to measure oxygen consumption and thermal tolerance of wild brown trout.

    We found that fish exhibited varying degrees of disease severity, with a wide range of parasite load, kidney swelling and associated anemia. Importantly, the aerobic scope, which is the maximum amount of usable energy a fish can produce using its aerobic metabolism, was negatively correlated with the severity of PKD. In addition, the thermal tolerance of the fish was also negatively correlated with disease symptoms. Our results demonstrate how a wild fish population can be at risk under the double threat of increased water temperature and expanding parasite range, and of their interaction. Understanding if and how local populations can adapt to these selective pressures will be critical to assess the long term evolution of this type of ecosystem.

    Image caption: Ecologist at work. 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.

     

    The effect of egg size on hatch time and metabolic rate: theoretical and empirical insights on developing insect embryos

    James L. Maino, Elia I. Pirtle, and Michael R. KearneyGumleaf Grasshopper from Australia’s Dry Eucalypt Forest. This grasshopper resembles a dry gum leaf and lays its eggs in the leaf litter. Photograph by James Maino.

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    As organisms change in size, they much also change in design to compensate for the mismatched scaling between surface-area and volume-based processes. Body size scaling relationships, combined with metabolic theory, allow biologists to study ecological phenomena in terms of processes at the organism level. By properly understanding biological processes at one level, higher level processes are able to be predicted and, in doing so, a mechanistic understanding is achieved. In this study we present a model based on simple energy and mass transfer processes during egg development that is able to explain how hatch time varies with species size and the time course of metabolic rate from egg lay to hatch. Our findings suggests that previous models made unrealistic assumptions regarding the metabolic activity of a freshly laid egg, leading to unreliable predictions. Metabolic theory is increasingly being applied in biology to understand a range of biological phenomena. Contributing to its success is its emphasis on the currencies of mass and energy, which are relevant at all scales of biology from the molecular to the ecosystem. Our presented model and supporting data on 98 species of insects advances our mechanistic understanding of egg development and highlights the usefulness of process-based models from which higher levels patterns can be derived.

    Image caption: Gumleaf Grasshopper from Australia’s Dry Eucalypt Forest. This grasshopper resembles a dry gum leaf and lays its eggs in the leaf litter. Photograph by James Maino.
    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.

     

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

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

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

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

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

     

    Do thermoregulatory costs limit altitude distributions of Andean forest birds?

    Gustavo A. Londoño, Mark A. Chappell, Jill E. Jankowski and Scott K. Robinson Andean cock-of-the-rock. Image provided by authors.

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    Tropical mountains contain the highest regional bird diversity in the world, largely because of high turnover of species with narrow altitudinal ranges. Understanding the mechanisms that limit so many species to narrow altitudinal distributions in the Andes is the central goal of our study. Our research is the first experimental approach to understanding the role of thermal physiology in limiting species’ altitudinal distributions. The biologist Daniel Janzen in 1967 hypothesized that tropical organisms should be specialized to a narrow range of temperatures because they experience little climatic variation in their ranges. As a result, they should be intolerant of temperatures outside of the optimal range, which would inhibit up- or downslope movements. Some tropical ectotherms (cold-blooded animals) fit Janzen’s predictions, but we do not know if endotherms, which maintain a constant internal temperature, are also excluded from environments outside their optimal temperature range. We measured several aspects of thermal physiology of 215 bird species across a 2.6-km altitude gradient in the Peruvian Andes. We predicted that highland species would show adaptation to the colder high-altitude climate, and that energy costs of thermoregulation might limit up-slope dispersal of lowland natives.

    We found reductions in thermal conductance (amount of heat loss) and body temperature, and lower critical temperature (lowest temperature where metabolism increases) in highland birds compared to lowland species, all of which make birds of high elevations more resistant to heat loss. We did not, however, find convincing evidence that acute thermal limits or energy costs of thermoregulation constrained altitudinal distributions. However, to evaluate the amount of energy that low elevation birds would spend at high elevation, we built heat budget models that predicted low-to-moderate long-term costs at native altitudes. Costs increased for lowland natives modeled in the highland climate, but for all but a few species, these higher costs remained within putative expenditure limits as defined in the literature.

    Although we did not test heat tolerances, we measured all species at temperatures similar to the hottest air temperatures at the lowland site. The lack of difference in basal metabolic rate at 30-34ºCdoes not suggest that high lowland temperatures preclude down-slope movements of highland birds. While thermal tolerances probably do not directly determine altitude occupancy by most species, there may be a tradeoff between the higher costs of thermoregulation experienced by lowland species moving up-slope and investment in important life history components such as breeding.

    Image caption: Andean cock-of-the-rock. 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 plant you choose to make your home isn't always the one that protects you best

    Jared G. Ali & Anurag A. Agrawal Image provided by authors.

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    A herbivore’s ability to feed, avoid predation, and succeed on specific host plants are some of the most important factors in its life. What we find, though, is that not all herbivores are able to perform equally well on every plant they encounter. Therefore, we assume most herbivores have specialized on plants that allow them to achieve optimal measures of performance. An important question that remains in ecology is whether herbivores select hosts more because of interactions with their host alone (nutrition, plant defenses, growth, etc.) or if predators and parasites play a major role in the selection of a plant host. A very interesting phenomenon occurs in many herbivores that specialize on particular hosts; they often gain the ability not only to cope with plant defenses (toxins produced to ward off herbivores), but to also steal them and keep them in their bodies to protect themselves from their own enemies. In this experiment we tested two specialized insect herbivores’ ability to perform on alternative plant hosts. We evaluated their performance while measuring toxins that these specialist herbivores steal from plants that might protect them from parasitic worms. We find specialization is driven primarily by plant-herbivore interactions, rather than by threat of predation/ parasitization, and that not all measures of performance are highest on the herbivores’ preferred host plants. This tells us that measures of performance are complex and that ecological interactions between a plant and host are not always those that result in optimal performance on every trait.

     

    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.

     

    Movement correlates of lizards' dorsal pigmentation patterns

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

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

    Image caption: Photo provided by authors.
    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.

     

    Testosterone and the cloacal microbiome in a free-living bird

    Camilo Escallón, Matthew H. Becker, Jenifer B. Walke, Roderick V. Jensen, Guy Cormier, Lisa K. Belden, Ignacio T. Moore Image provided by authors.

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    Testosterone is a hormone that primarily functions to regulate reproduction in male vertebrates. It mediates processes such as sperm production, development of sexually-selected traits, and reproductive behaviors. There are many benefits for males maintaining high testosterone levels. However, it has been argued that maintaining high testosterone levels for prolonged periods also has costs, and could ultimately have negative consequences for long-term survival. One of the proposed pathways by which testosterone can affect survival is by increasing the risk of infection, including pathogenic bacteria.

    We investigated testosterone and cloacal bacteria in free-living rufous-collared sparrows in the Ecuadorian Andes. Males of this species have high levels of testosterone during the breeding season, when they form socially monogamous unions with females. However, extra-pair paternity is common. We measured circulating testosterone concentrations, and assessed the diversity and types of bacteria living in their cloaca, which in birds functions as the opening from the gastrointestinal tract and is also the copulatory organ. Thus, it harbors bacteria that can be sexually transmitted.

    We found that birds with higher levels of testosterone also had higher cloacal bacterial diversity, and had higher relative abundance of Chlamydiae, a group of bacteria that can be pathogenic. In addition, the cloacal microbes of low-testosterone birds were different from the rest of the males, seemingly because they were missing some bacteria that the other birds possessed. Two nonexclusive explanations for these results are that testosterone affects behaviors that lead to increased sexual contacts, and thus increased exposure to bacteria, or that testosterone is altering the bird’s immune system, thus making it easier for bacteria to colonize. Either way, these results suggests that increased exposure to sexually-transmitted pathogens in the form of cloacal bacteria could be a cost of maintaining high testosterone levels.

    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.

     

    Host phenology and potential saprotrophism of ectomycorrhizal fungi in the boreal forest

    Stefan F. Hupperts, Justine Karst, Karin Pritsch, Simon LandhäusserMature aspen trees during late summer, when leaves are fully expanded and photosynthesizing at full capacity. Carbon allocation to ectomycorrhizal fungi is likely high during this phenological stage. Photo credit: Erin Wiley.

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    Ectomycorrhizal plants allocate some of their photosynthetically derived carbon to ectomycorrhizal fungi - organisms that colonize roots and provide mineral nutrients to their plant hosts in return for carbon compounds. With the onset of spring, trees will develop leaves for photosynthesis and then drop their leaves in autumn when temperatures decrease and daylight shortens. These seasonal changes in photosynthetic capacity induce fluctuations of carbon stored in tree roots, and may therefore influence the amount of carbon provided to ectomycorrhizal fungi.

    Though traditionally considered dependent on living trees for carbon, recent work suggests that ectomycorrhizal fungi may be able to mobilize carbon from soil organic matter and plant litter (i.e. become saprotrophic). Two competing models exist to explain carbon mobilization by ectomycorrhizal fungi. Under the ‘saprotrophy model’, decreased allocation of carbon may induce saprotrophic behavior in ectomycorrhizal fungi, resulting in the decomposition of organic matter to provide the fungus with carbon if the supply from the host plant is inadequate. Alternatively, under the ‘nutrient acquisition model’, decomposition by ectomycorrhizal fungi may instead be driven by the acquisition of nutrients, such as nitrogen and phosphorus, locked within soil organic matter compounds, with carbon mobilization a secondary process.

    We tested whether phenology-induced shifts in carbon reserves of fine roots of aspen affect potential activity of carbon-compound degrading extracellular enzymes by ectomycorrhizal fungi. Ectomycorrhizal roots from mature aspen were collected across eight sites in northeastern Alberta, Canada and analyzed during four distinct phenological stages: winter, spring, summer, and autumn. We predicted potential activity of carbon-compound degrading enzymes would be highest when root carbon reserves were lowest, should host phenology induce saprotrophism.

    We found activity of EMF-derived carbon-compound degrading enzymes to be relatively constant across phenological stages. Furthermore, low-biomass ectomycorrhizal fungi appear to have a greater ability to degrade complex carbon compounds when compared to high-biomass ectomycorrhizal fungi. These findings support the nutrient acquisition model, and suggest that the degradation of soil organic matter and plant litter by ectomycorrhizal fungi is driven by nutrient foraging rather than saprotrophy.

    Image caption: Mature aspen trees during late summer, when leaves are fully expanded and photosynthesizing at full capacity. Carbon allocation to ectomycorrhizal fungi is likely high during this phenological stage. Photo credit: Erin Wiley.
    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.

     

    New ranking algorithm can identify overall pattern from incomplete surveys, providing critical insight into complex problems

    Timothy D. Swain, John Chandler, Vadim Backman, Luisa MarcelinoPhoto by Luisa A. Marcelino.

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    As the third global coral bleaching episode is currently ongoing and expected to kill thousands of square kilometers of coral reefs, our ability to understand why some corals are killed while others survive is hampered by our capacity to consolidate previous knowledge. Corals are a combination of simple animals and algae that work in highly efficient unison to collect sunlight to make food. This association is sensitive to changes in temperature; when stressed by heat, the combination unravels in the bleaching response, leaving corals weakened and starving. Rising ocean temperatures caused by global climate change have made bleaching more frequent and severe, and understanding the mechanisms underlying the bleaching response is an urgent ecological problem. It is known that the algae associated with coral are highly diverse, and that some types are better at helping corals resist thermal stress than others. This insight originates from many experiments and surveys that, for reasons necessitated by the biology of the organisms themselves, can only provide detailed information on small subsets of the algae types; meaning that we know a lot about the relative performance of short lists of algae types, but almost nothing about the relative performance of all types. It turns out that this problem, of having lots of information about the ranking of small partial lists and little information about the ranking of an entire population, is common in many fields including search engines, election schemes, ‘best of’ rankings, and theoretical and applied sciences and engineering. To overcome this problem we devised a new ranking algorithm that can accept these partial lists and return a consensus ranking of all the elements in the lists even when there are disagreements among lists. We also validated the performance and accuracy of the algorithm with known rankings; the algorithm is very robust at uncovering new comparisons absent from the initial lists and has a low misranking error. This novel tool has broad application potential to a variety of ranking problems and will provide critical insight into coral bleaching mechanisms.

    Image caption: Photo by Luisa A. Marcelino.
    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.

     

    Fire impacts on soil organisms

    Jennifer L. Soong, Marie Dam, Diana H. Wall, M. Francesca CotrufoImage provided by authors.

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    Fires occur in nearly all terrestrial ecosystems. The occurrence rate and severity of fires depends on many factors. One important impact of fires is the combustion of aboveground plant material. This plant material would typically die and be considered “litter” to be decomposed by soil microbes and other organisms, such as nematodes, who help to recycle the nutrients held in the litter for subsequent plant production. When plant litter is combusted during a fire, much of its biomass is volatilized and lost from the ecosystem but a small fraction remains as partially burned residues, or the black charred material remaining on the soil surface after a fire. Here we used pyrolized organic matter as a substance resembling the charred material left behind by fires.

    We examined how soil microbes, nematodes and plant roots use organic matter from decomposing litter and pyrolized organic matter in order to understand how the alteration of decomposition inputs to the soil by burning affects soil biological processes. We found that while litter provides a carbon and nitrogen food source to soil microbes, nematodes and growing roots, pyrogenic organic matter remains in the soil mostly unused. We also saw that this litter food source shifts the structure of the belowground food web. These results help to explain the impact of fire on belowground biological processes. For example, if aboveground biomass is removed during fires there is less material remaining to fuel belowground organisms, and the partially combusted material remaining is not easily decomposed and recycled.

    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.

     

    Phytopathogens affect plant volatile emissions and the attraction of parasitoid wasps

    Camille Ponzio, Berhane T. Weldegergis, Marcel Dicke and Rieta GolsThe parasitic wasp Cotesia glomerata, parasitizing on 1st instar larvae of the large cabbage white butterfly, Pieris brassicae. Photo copyright Hans Smid / Bugsinthepicture.com.

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    As natural enemies of plant feeding insects, parasitoid wasps lay their eggs in the bodies of these other insects, and develop inside. The wasps find their herbivorous hosts by using plant odors to find the infested plant. When a plant is attacked by an insect herbivore, the volatile odors that it emits are modified, and these changes provide the foraging wasps with important information on the location of its hosts. If more than one species of insect herbivore attacks the plant, this can affect the plant odors, and in turn affect the ability of the wasps to find hosts.

    However, plants are attacked not only by insects, but also by plant pathogens, and these can also change the odor of the plants. This has been rarely studied, and researchers usually focus on plant pathogens that cause disease. Yet plants can also be resistant to a pathogen, and this may also affect the emitted plant odors.

    We investigated how two strains of a plant pathogen, with the plants resistant to one and susceptible to the other, affected the composition of the induced odors and the ability of the wasps to find their hosts. We studied plants infected either with a pathogen, caterpillar hosts of the wasps, or a combination of both. We found that the two strains produced odors that were different from each other, but that the odors from plants infected with the disease-causing strain were similar to the odors induced by feeding caterpillars. The parasitoid wasps preferred plants that had both caterpillars and a pathogen over plants with only caterpillars, and they were even attracted to odors from plants challenged with only a pathogen.

    This research shows that plant pathogens can have as strong influence as insects on plant odors and their use by parasitoids. It is important to combine research on plant-insect and plant-pathogen interactions in the future if we are to have a better understanding of how plants defend themselves against both types of attackers.

    Image caption: The parasitic wasp Cotesia glomerata, parasitizing on 1st instar larvae of the large cabbage white butterfly, Pieris brassicae. Photo copyright Hans Smid / Bugsinthepicture.com.
    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.

     

    Linking the respiration of fungal sporocarps with their nitrogen concentration: variation among species, tissues, and guilds

    Lidia K. Trocha, Elżbieta Rudy, Weile Chen, Miroslawa Dabert, David M. EissenstatMeasuring respiration of a piece of sporocarp of Lactarius sp. using the the oxygraph: a chamber containing the silver electrode which detects oxygen consumption; photo captured by Lidia Trocha.

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    Respiration (RS) has been widely correlated with tissue nitrogen concentration in plants. Worldwide results show positive N-RS relationships across plant species, plant functional groups, and plant organs. We wanted to determine if similar responses exist in fungal sporocarps (spore-producing bodies) either among fungal species representing different guilds (ectomycorrhizal, saprotrophic, and parasitic) or between fungal caps and stipes representing different “tissues”.

    Similar to plants, fungal sporocarps exhibit positive N-RS relationships across 93 species, which was consistent across fungal guilds, and across fungal “tissues”. However, in contrast to plants, nitrogen concentration could only explain relatively little (26%) of the RS variation among fungal species. This result may reflect fungal sporocarp nitrogen allocation, which may be partially metabolically inactive.

    Forest fungi belonging to different guilds (ectomycorrhizal, saprotrophic, and parasitic) gain food through diverse strategies: by decomposition of organic matter (saprotrophic) or through symbiosis with plants (ectomycorrhizal and parasitic). Thus, feeding strategy of a fungus influences fungal metabolic activity as different amounts of energy resources are required depending on the chemical recalcitrance of the food source.

    We found that fungal guild can be linked to sporocarp respiration and nitrogen concentration. Saprotrophic species have the fastest respiration and highest N concentration and ectomycorrhizal species have the lowest, with parasites intermediate. We also found that caps are more active than stipes, which reflects sporocarp “organ” specification: the caps are responsible for producing spores, while stipes mostly lift the caps.

    Image caption: Measuring respiration of a piece of sporocarp of Lactarius sp. using the the oxygraph: a chamber containing the silver electrode which detects oxygen consumption; photo captured by Lidia Trocha.
    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.

     

    Limited flexibility in heat tolerance suggests vulnerability to climate change

    Belinda van Heerwaarden, Vanessa Kellermann and Carla M. SgròPhotograph provided by author.

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    Rises in average temperature (as much as 2-4° C), as well as increases in the frequency of extreme temperature events, are likely to pose a major risk to many species. Tolerance of high temperatures is flexible (plastic) and can change depending on the temperatures a species encounters prior to experiencing stressfully high temperatures. Whether flexibility (plasticity) in heat tolerance can buffer the increases in temperature predicted with climate change is not known. We examined the plasticity of heat tolerance in tropical and temperate flies exposed to constant or fluctuating temperatures that reflect average temperatures experienced in nature during development (developmental plasticity), as well as after a short term stressful, but not lethal, temperature as adults (hardening plasticity) representing extreme high temperature events. While we observed some increases in heat tolerance when flies were exposed to higher average temperatures during development (developmental plasticity) and extreme temperatures as adults (hardening plasticity), heat tolerance was improved only by a maximum of 1.01° C. These results imply that overheating risk will only be minimally reduced by plasticity in heat resistance. We also found that increased heat tolerance after exposure to short term non-lethal stressful temperatures (hardening) was lower in flies exposed to warmer average developmental temperatures, indicating that increases in heat resistance at warmer temperatures may come at the cost of a reduced capacity to respond to short term extreme heat events via hardening plasticity. This study suggests that plastic increases in heat tolerance, particularly at warmer temperatures, may not be sufficient to keep pace with temperature increases predicted under climate change.

    Image caption: Photograph provided by author.
    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.

    Ecosystems, Evolution, and Plant Soil Feedbacks

    Eco-evolutionary feedbacks in an invasive plant

    Jeffrey A. Evans, Richard A. Lankau, Adam S. Davis, S. Raghu and Douglas A. Landis Photograph provided by authors.

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    Ecological and evolutionary processes are often assumed to operate at very different speeds. People typically think of ecological interactions as fast (such as a predator hunting for prey or two plants competing for water). In contrast we usually think of evolutionary change as very slow (for example, it took many millions of years for mammals to evolve from reptiles). But these processes can, in fact, both work relatively quickly and affect each other on mutually relevant time scales. We call these eco-evolutionary feedbacks. Our study shows how an eco-evolutionary feedback between population growth and plant chemistry shapes the invasion process in a weedy invasive plant, garlic mustard (Alliaria petiolata).

    Garlic mustard produces a chemical called sinigrin that it releases into the soil, where it acts as a competitive “weapon” against other plant species early in the invasion process. We show that garlic mustard plants that produce more sinigrin have higher survival rates early in their life cycle, particularly as seedlings and during the summer. These life history stages are important drivers of population growth. Populations that produce more sinigrin grow and spread faster and ultimately reach higher plant densities. Once an established population has pushed out other competitors though, garlic mustard plants primarily compete with each other. Because sinigrin is only useful to garlic mustard in competition with other species, populations evolve to produce less sinigrin as they age. These lower-sinigrin populations grow and spread more slowly and have lower average plant densities.

    Our results illustrate how the evolution of a trait (sinigrin production) can influence the ecology of a species over periods from just a few years to decades, altering its trajectory of population growth and interactions with other species in the soil and the plant communities it invades. They confirm predictions that eco-evolutionary feedbacks occur in natural populations. Furthermore, they improve our conceptual understanding of what drives population growth, by highlighting the relationship of survival and reproduction to a critical competitive trait whose advantages decrease as populations age.

    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.

     

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

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

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

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

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

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

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

     

    Litter microbial and soil faunal communities stimulated in the wake of a volcanic eruption in a semiarid woodland

    Paula Berenstecher, Daniela Gangi, Adelia González-Arzac, M. Laura Martínez, Eliseo J. Chaves, Eduardo A. Mondino and Amy T. AustinMeliquina Valley, Argentina, several months after the massive eruption of the Puyehue volcano in December, 2011.  This site is approximately 70 km from the epicenter of the eruption.  The area is a mixture of natural woodland vegetation and exotic ponderosa pine (Pinus ponderosa) plantations.  Inset shows depth of ash deposition in the woodland ecosystem. Photo courtesy of P. Berenstecher.

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    Large-scale natural disturbances, such as hurricanes, fires, frosts and volcanic eruptions, are important factors that affect natural ecosystems, but generalities regarding their effects are difficult due to their infrequent and unpredictable nature. Volcanic eruptions figure as one of the most prominent of these natural disturbances, but the effects on microbes and soil fauna (ground-dwelling arthropods, such as ants, beetles or mites, and nematodes, microscopic round-worms) are relatively unknown. These organisms are important because they are key players in the formation of soil organic matter and turnover of nutrients which then become available for plants. We evaluated ecosystem changes induced by the dramatic Puyehue-Cordón Caulle eruption of June 2011 in Patagonia, Argentina. We were interested in how these microbes and soil animals responded to heavy ash deposition in both natural woodland vegetation and a pine plantation in the Meliquina Valley, located 70 km west of the epicenter of the eruption. As ash can be quite abrasive and is, in fact, used as an insecticide, we hypothesized that volcanic ash deposition would have marked negative effects on the soil biota and consequently on decomposition. We were extremely fortunate to have made pre-eruption measurements in the same sites in the year prior to the volcanic eruption, which provided a rare opportunity to make a real comparison before and after the ash deposition.

    We measured environmental variables of soil and litter (moisture, pH, organic matter) and biotic variables (abundance of ground-dwelling arthropods, nematodes, microbial biomass and microbial activity in soil and litter) in both natural woodland and pine plantation sites. We were surprised to find that ground-dwelling arthropods actually dramatically increased in abundance after the eruption, while soil nematodes were negatively impacted. More surprising, however, was that evaluating the effects of ash on litter decomposition showed more than doubled rates of carbon turnover in litter from the native woodland. It seems that the effect of the ash deposition may be related to your habitat, with those who reside in the soil being negatively affected while the litter dwelling microbes and fauna were actually favoured by the conditions of the eruption. This study provides insight into the effects of large disturbances on the underappreciated soil biota, and highlights that these disturbances do not always result in the catastrophic effects that we might imagine.

    Image caption: Meliquina Valley, Argentina, several months after the massive eruption of the Puyehue volcano in December, 2011. This site is approximately 70 km from the epicenter of the eruption. The area is a mixture of natural woodland vegetation and exotic ponderosa pine (Pinus ponderosa) plantations. Inset shows depth of ash deposition in the woodland ecosystem. Photo courtesy of P. Berenstecher.
    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.

     

    Using functional responses to quantify interaction effects among predators

    Ryan J. Wasserman, Mhairi E. Alexander, Tatenda Dalu, Bruce R. Ellender, Horst Kaiser and Olaf L.F. WeylSouthern mouthbrooder (Pseudocrenilabrus philander- foreground) and banded tilapia (Tilapia sparrmanii- background). Photo provided by authors.

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    The relationship between prey consumption by a predator and prey availability is known as the functional response. Functional response studies on predators are useful as they provide valuable information on the nature of prey consumption by a predator. For example, the proportion of prey that a predator consumes when there are lots of prey around may be different to the proportion consumed when there are few prey. This is because some predators are better at finding prey at low densities than others, while certain predators are particularly good at eating lots of prey when they are available. Understanding differences amongst predators is important as across most ecosystems, biodiversity levels are changing as a result of extinctions and invasions associated with anthropogenic activities. This is also true for predatory species and many environments have been altered to the point where predatory species have been either lost or gained. It has been shown that predators interact with one another and interactions among predators can diminish or enhance their effects on prey, depending on the nature of the interaction between the predators. These are known as multiple predator effects (MPEs) and are relevant within the context of predator species loss or gain.

    While functional response and MPE studies are common in the literature and their value is well recognised, few studies have assessed both aspects of predation simultaneously. In a laboratory study we use three fish species with different functional traits as model predators (bluegill Lepomis macrochirus, southern mouthbrooder Pseudocrenilabrus philander and banded tilapia Tilapia sparrmanii) and assess intra- and inter-specific predator interaction outcomes on predator-prey dynamics. We contrasted the observed functional responses of combinations of predators, of the same or different species, with expected responses based on those of individual predators. We show that prey risk varies as a result of predator-predator effects, both within and between species. This study therefore represents a step closer to real world scenarios where multiple predators interact with one another, and with prey at different prey densities. We therefore propose that the incorporation of predator combinations into classic functional response investigations would be useful for the development of competition and predation ecology.

    Image caption: Southern mouthbrooder (Pseudocrenilabrus philander- foreground) and banded tilapia (Tilapia sparrmanii- background). 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.

     

    Fertilization changes goldenrod’s defensive response to grasshoppers

    Karin T. Burghardt Photo credit: Karin T. Burghardt.

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    Most plants are not able to actively move away from animals that want to eat them, however they are far from passive in their response. Many species can reduce herbivore feeding by producing an arsenal of chemical and structural anti-herbivore defenses. Such resistance may always be produced by a plant at baseline levels or only after an herbivore attacks. Alternatively, a plant can tolerate herbivore damage and simply reallocate resources to promote regrowth, thereby minimizing the negative impact of the herbivore on reproduction. The strategy a plant uses may depend on nutrient availability because the cost-benefit trade-off between growth and defense changes across nutrient environments.

    In this study, I investigated how defensive strategy changes across a nutrient (fertilization) gradient within tall goldenrod. This plant is an extraordinarily common species found within abandoned fields and along roadsides across eastern North America. Clones of 9 genotypes (collected from an old-field) were grown in a greenhouse at varying nutrient levels and some were exposed to grasshoppers collected from the same field.

    I found that genetically identical individuals changed their defensive strategy across the nutrient gradient. At low nutrient levels, plants tolerated herbivory and exhibited low to moderate levels of baseline resistance. In contrast, fertilized plants did not invest in baseline resistance, opting to wait and invest in high levels of resistance only when attacked by grasshoppers. It is important to note that plant defensive trait changes occur within the context of many other whole-plant changes. Therefore, I also studied how a plant’s defensive strategy changed in concert with 26 other plant traits including leaf nutrient content and belowground allocation.

    This study highlights how flexible genetically identical plants can be in terms of resource allocation patterns across developmental environments. In addition, quantifying the way in which a dominant species alters traits in response to nutrients enables us to predict how human-caused nitrogen deposition (a known occurrence in the northeastern U.S.A) will impact old-field communities. Finally, understanding how soil nutrient environment changes plant defensive traits and productivity is of critical importance to agriculturists interested in reducing pesticide use while maximizing yield.

    Image caption: Photo credit: Karin T. Burghardt.
    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.

     

    Predator-prey mass ratio revisited: Does preference of relative prey body size depend on individual predator size?

    Cheng-Han Tsai, Chih-hao Hsieh and Takefumi NakazawaPhoto provided by authors.

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    Food webs are complex systems including many species and interactions and thus are difficult to understand. A promising way of understanding food-web dynamics and their responses to environmental changes is to focus on body size relationships between interacting predator and prey, because their relative body sizes (i.e. predator-prey mass ratio, abbreviated as PPMR) largely determine the strength of predator-prey interactions. Specifically, it is expected that predators should not eat too big or too small sized prey. If we know the optimal relative prey size, it may help to simplify the structure of complex food-web models and allow us to more easily assess food-web responses to environmental changes. This optimal relative prey size is called preferred PPMR.

    So far, previous studies of several dietary datasets have reported that PPMR increases with predator body size, meaning that large predators consume proportionally smaller prey. Problematically, this pattern contradicts the conventional assumption that all predators should have a similar value of preferred PPMR, and thus those studies have argued that more complex food-web models are needed to better describe food-web dynamics.

    However, we point out that this apparent inconsistency arises because previous measurement of PPMR have been based only on dietary data (i.e. realised PPMR in diet) and have not appropriately assessed prey size selectivity of predators (i.e. preferred PPMR) by considering effects of prey composition in the environment. In this study, comparing long-term changes in prey size composition in both the diet and the environment of a fish species, we appropriately assessed preferred PPMR for the first time, and observed that preferred PPMR does not vary with predator body size, in accordance with the original theoretical expectation. Although this is a case study using a single predator species, our findings represent an important first step in establishing size-based food-web studies. In addition, our approach can be generally applied to other species and systems, which would allow us to test the plausibility of previous theoretical predictions based on the assumption of size-invariant preferred PPMR.

    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.

     

    How bark properties promote invertebrate diversity in tree logs during early decay

    Juan Zuo, Matty P. Berg , Roy Klein, Jasper Nusselder, Gert Neurink, Orsi Decker, Mariet M. Hefting, Ute Sass-Klaassen, Richard S. P. van Logtestijn, Leo Goudzwaard, Jurgen van Hal1, Frank J. Sterck, Lourens Poorter, Johannes H. C. Cornelissen One incubation plot of LOGLIFE experiment in Hollandse Hout, province of Flevoland, the Netherlands. Photograph by J. Zuo.

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    Temperate forests accumulate large numbers of tree logs, which play important roles for biodiversity. They host a large number of organisms that need decaying bark or wood for food, shelter or reproduction. Among these organisms, invertebrates are a vital group with a fascinating diversity and an important role in the decay process of dead trees itself. The factors that determine invertebrate community composition in logs are still not clear. In recently dead tree trunks, the attached bark is of critical importance. The large variation in bark structure and tissue quality observed among tree species may determine invertebrate community composition by providing variation in resources and habitats.

    We investigated the effects of bark properties, during the early decay stage of logs, on invertebrate community structure of 11 common, temperate tree species in the LOGLIFE ‘common garden’ experiment, in which logs of all these trees were placed in the same forest plots at the same time. We measured several bark properties and studied their effects on six animal groups: earthworms, woodlice, centipedes, millipedes, flies/midges and beetles. We hypothesized that, across tree species, the more different the bark properties were between two species, the more the composition of the animal community would differ as well.

    Our tree species varied greatly in seven different bark properties, which had profound effects on the abundance of specific invertebrate groups. The greater the overall difference in the bark properties between tree species, the more dissimilar were the animal communities they supported, and the richer they were together in different invertebrate families. Bark properties have important effects on the composition and diversity of invertebrate communities in recently dead and decaying tree trunks. Our findings indicate that functional diversity in bark properties in decaying logs is likely a good indicator, better than tree species per se, of animal diversity in forests.

    Image caption: One incubation plot of LOGLIFE experiment in Hollandse Hout, province of Flevoland, the Netherlands. Photograph by J. Zuo.
    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.

     

    Relative importance of soil properties and microbial community for soil functionality

    Manuel Delgado-Baquerizo, Jasmine Grinyer, Peter B. Reich and Brajesh K. SinghImage provided by authors.

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    Soil ecosystem functionality is usually divided into two groups of functions: broad (i.e. widely conducted by all or most living organisms) and specialized (i.e. conducted by particular groups of organisms). The most widely accepted theories in soil ecology suggest that broad (e.g. respiration) and specialized (e.g. denitrification – reduction of nitrate, ultimately to nitrogen) functions are affected differently by resource availability and microbial communities in terrestrial ecosystems. However, we lack solid empirical data to quantify the relative importance of microbial communities and soil properties in regulating soil functions. Here we conducted a manipulative experiment and used statistical modeling to evaluate the role of soil properties and microbial communities in driving broad and specialized functioning. Our results provide direct experimental evidence that soil microbial community plays an important role in determining the rates of both broad (soil respiration) and specialized (denitrification) functions. In particular, our findings indicate that for broad functioning, soil properties such as total carbon can play a bigger role than the microbial community composition. Contrary to this, bacterial community composition drove the rates of specialized functioning, regardless of soil properties. These results support the most widely accepted soil ecological theories that suggest that broad functions such as soil respiration, which are a product of widely distributed processes across living microorganisms, are limited by both resource availability and microbial abundance. But specialized functioning, which is conducted by particular groups of organisms, may be highly sensitive to changes in microbial community. Such evidence helps advance our understanding of different drivers of soil ecosystem functioning, which will be crucial to developing an ecologically-relevant theory about belowground ecosystem functioning.

    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.

     

    Are dive bottom durations good indicators of fur seal foraging success?

    Morgane Viviant, Tiphaine Jeanniard-du-Dot, Pascal Monestiez, Matthieu Authier and Christophe GuinetArctic fur seal. Photograph by Christophe Guinet, CEBC UMR 7372 ULR-CNRS.

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    Foraging models applied to air breathing divers predict that diving predators should optimize the time spent foraging at the bottom of dives, depending on prey encounter rate, distance to the prey patch (depth) and physiological constraints. This hypothesis was tested in free-ranging diving Antarctic fur seal Arctocephalus gazelle, equipped with accelerometers or Hall sensors that recorded mouth-opening events, an indicator of feeding events. 82 % of mouth-openings, defined as prey catch attempts, occurred at the bottom of dives. In accordance with model predictions, fur seals increased their foraging time at the bottom of dives with increasing diving depth, irrespective of the number of mouth-openings events. For dives shallower than 55 m, the mean bottom duration of dives without mouth-opening events was shorter than for dives with mouth-opening events. However, this difference was only due to the occurrence of V-shaped dives with very short bottom durations (0 or 1 s). When those V-shaped dives are removed, bottom duration was no longer related to the presence of prey capture attempts. Thus, the decision to abandon foraging is likely related to other information about prey availability than mouth-opening events (i.e. visual, sensory or acoustic cues), that seals might start collecting during the descent phase. For dives deeper than 55 meters, seals keep on foraging at bottom to maintain a greater diving efficiency as there is no longer any benefit of giving up. Most dives occurred at shallower depths (30-55 m) than the depth of highest foraging efficiency (i.e. of greatest number of mouth-opening events detected per dive, below 60 m). This is likely related to physiological constraints linked to deeper dives. These findings suggests that foraging decisions are more complex than predicted by current theory and highlight the importance of the information collected by the predator during the descent as well as physiological constraints.

    Image caption: Arctic fur seal. Photograph by Christophe Guinet, CEBC UMR 7372 ULR-CNRS.
    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.

     

    Stable isotopes reveal the ecology of tropical butterfly larvae.

    Erik van Bergen, Henry S. Barlow, Oskar Brattström, Howard Griffiths, Ullasa Kodandaramaiah, Colin P. Osborne and Paul M. BrakefieldEcologists at work. Photo provided by author.

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    Despite many ecological studies, our understanding of the larval ecology of many tropical butterfly species is very limited. In contrast to adults, caterpillars are mainly active at night and are notoriously hard to spot in the wild. This seriously hampers investigations of the evolution of feeding ecology and potential co-evolutionary interactions between host plants and butterflies. One group of butterfly species that is particularly interesting in the context of plant-herbivore co-evolution is the subtribe Mycalesina (Nymphalidae). These tropical butterflies feed mainly on grasses as larvae and have radiated dramatically in Sub-Saharan Africa, Madagascar and Asia with over 300 extant species.

    The commonest form of photosynthesis is called C3, but tropical grasses often have a variant called C4, and the evolutionary history of mycalesine butterflies is expected to be closely tied to the rapid replacement of C3 vegetation by C4 grasslands in the Late Miocene-Pliocene. In contrast to C3 host plants, these C4 grasses tend to have a higher physical toughness and lower nutritional values. Therefore, insect herbivores, such as mycalesine larvae, are expected to avoid C4 grasses when C3 host plants are available. In addition, one would predict that novel feeding adaptations, for instance in jaw morphology or digestive physiology, may have evolved in mycalesines in response to the ecological dominance of C4 grasses in open savannah habitats.

    Stable isotope analyses represent an unexploited opportunity to increase our understanding of the larval ecology of mycalesine butterflies. The environmental conditions to which a caterpillar is exposed are imprinted into the exoskeleton of the adult during metamorphosis. By measuring the ratios of several stable isotopes we can recover the information that is ‘recorded’ in leg material (=exoskeleton) of adult butterflies, which are relatively easy to capture in the wild. Here, we show that stable isotopes of carbon provide information about the type of host plant, C3 or C4, which was used by the larvae. In addition, stable isotopes of oxygen reveal how much water vapour was present in the atmosphere during larval development.

    The isotopic composition of leg tissue in mycalesine butterflies shows that species that inhabit open C4 grass-dominated environments are quite opportunistic in their larval host plant choice. Nevertheless, we observe that during the dry season, larvae are more likely to use high quality C3 grasses and are exposed to lower levels of water vapour in the atmosphere. Finally, our data reveal that the ability to process C4 grasses is clustered within related groups of mycalesine species, suggesting that C4 grass processing adaptations may have evolved in this subtribe.

    Image caption: Ecologists at work. Photo provided by author.
    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.

     

    Mycorrhizal and saprotrophic fungal guilds compete for the same organic substrates but affect decomposition differently

    Inga TM Bödeker, Björn D Lindahl, Åke Olson and Karina E ClemmensenThe soil profile of the boreal forest near Sala in middle Sweden in which the field study was conducted. The soil has a 10-25 cm thick organic layer on top of the mineral soil. Photo by KEC.

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    Communities of litter saprotrophic (decomposer) and mycorrhizal fungi are vertically separated within boreal forest soil profiles, with litter saprotrophs normally confined to the fresh litter on the surface and mycorrhizal fungi dominating the deeper soil layers. It is unclear whether this depth partitioning is maintained exclusively by substrate-mediated niche partitioning, or by competition for space and resources. Improved understanding of the mechanisms driving spatial partitioning of these fungal guilds is critical, as they may affect carbon and nutrient cycling in different ways.

    We utilized the spatial separation of litter saprotrophic and mycorrhizal fungal communities to – under field settings – test the potential of these fungal guilds to colonize and exploit organic matter outside their normally realized niche. Natural substrates of three qualities – fresh or partly decomposed litter or humus – were incubated in mesh-bags in both their own and in ‘foreign’ locations in the soil profile. After one and two growing seasons we determined fungal community composition and decomposition activities in the substrates.

    During the first growing season, all organic substrates were mainly colonized by fungi native to the soil horizon in which the substrates were incubated. This demonstrated the potential of both fungal guilds to colonize all substrates, and suggests that their colonization under natural circumstances is restricted by competitive interactions. Litter substrates also decomposed more slowly when colonized by root-associated communities than when colonized by saprotrophs, suggesting that ectomycorrhizal fungi are less efficient than saprotrophic fungi in decomposing aboveground litter substrates.

    During the second growing season, certain basidiomycetes from both guilds were particularly efficient in localizing and exploiting their native organic substrates although displaced in the vertical profile. This resulted in a complete catch-up in decomposition of litter even when placed in the humus, showing that fungal communities – rather than microenvironmental conditions - were the primary drivers of slow decomposition of litter during the first season. Humus substrates were only slightly decomposed by both fungal guilds, and based on the present study we cannot resolve whether competitive interactions between fungal guilds are important for long-term soil C storage.

    Overall, fungal community development during the course of the experiment was determined to similar degrees by vertical placement and by substrate quality. While the importance of substrate quality on decomposer communities and their activities has long been acknowledged, our results suggest that competition and monopolization of spatial domains (as tested by the placement treatment) play a more important role in structuring fungal communities at small scales than previously thought. In natural ectomycorrhiza-dominated forest ecosystems, preferred substrates and territorial distribution of these fungal guilds thus coincide, and competition appears to reinforce the vertical, substrate-dependent partitioning and stabilize vertical community stratification.

    At the ecosystem level these findings suggest that ectomycorrhizal fungi through competitive interactions have the potential to indirectly regulate litter decomposition rates by restraining activities of more efficient litter saprotrophs. Vice versa, in situations where the competitive strength of mycorrhizal fungi is compromised – for example after forest clear-cuts – saprotrophs may proliferate and accelerate decomposition processes.

    Image caption: The soil profile of the boreal forest near Sala in middle Sweden in which the field study was conducted. The soil has a 10-25 cm thick organic layer on top of the mineral soil. Photo by KEC.
    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.

    Ecosystems, Evolution and Plant Soil Feedbacks

    Rapid evolution of plants and soil microbes

    Casey P. terHorst and Peter C. ZeePhotograph provided by authors.

    Ecologists have long appreciated the value of diversity in natural plant communities. Diverse communities function better. Yet, our understanding of the factors that control diversity in communities remains incomplete. We have recently begun to appreciate the important role of microbes in human health; plants too both rely on and battle with microbes in the soil. Plant diversity can affect the soil microbial community, but the microbes also affect plant diversity, in a feedback known as plant-soil feedback (PSF). Because of their short generation times and strong effects on each other’s ecology, plants and microbes can evolve on the scale of weeks to years. Here we review evidence of how changes in plant and microbial traits affect diversity and ecological dynamics in the community. Genetic variation in plant traits and subsequent evolution of those traits can affect traits and species composition of soil microbial communities. Soil microbial communities can, in turn, alter the evolutionary trajectory of plant traits. Finally, we consider how interactions between ecology and evolution might enhance or mitigate the effects of PSF in driving the diversity of natural plant communities.

    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.

    Advances and challenges in the study of ecological networks

    Evolutionary history imprinted on species interaction

    Guadalupe PeraltaThe leaf veins resemble the shape of species phylogeny which underlies the plant-leafminer interaction. Photo by G. Peralta.

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    In ecosystems, organisms interact with each other in diverse ways, forming complex webs of relationships. It is well known that the occurrence of interactions among species of a community depends on species co-occurrence and also on their abundance. However, apart from these factors, it has been suggested that the evolutionary history of species might also determine the interactions that occur within a community. If this was the case, information on species relatedness could improve our understanding of the mechanisms driving community structure and dynamics. In addition, if species relatedness is informative of the interactions that species have, this could be used as a tool for determining and predicting the effects that global environmental changes could have on communities. For instance, the effects of an invasive species could be forecast, and potentially reduced, if we could predict how that species would fit into the assemblage of interactions of the invaded community (i.e. if based on the relatedness of the invasive species with other species we could predict its partners).

    Therefore, in this paper I review the ecological literature in which species relatedness has been tested as a potential driver of the ensemble of interactions and its structure. It has been shown that species relatedness can affect different aspects of community structure differently and this imprint can also vary depending on the interaction type (e.g. antagonistic vs. mutualistic interactions).

    Thus, the evidence confirms that species interactions bear the stamp of their evolutionary history. Understanding the influence that species relatedness has on community assembly can help us to predict how communities might change and how they will function in the future.

    Image caption: The leaf veins resemble the shape of species phylogeny which underlies the plant-leafminer interaction. Photo by G. Peralta.
    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.

     

    Neighboring resources can affect the attractiveness of resources occurring in the neighborhood

    Thomas A. Verschut, Paul G. Becher, Peter Anderson and Peter A. Hambäck  Photo credit: Sébastien Lebreton.

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    Plants often differ in their quality as a food resource for insects. As many insects find food through smell, a plant with a very attractive smell will attract a higher number of insects than a plant with a less attractive smell. However, when an attractive plant grows next to an unattractive plant it can lead to an increased number of insects visiting the unattractive plant, which is known as associational susceptibility. Moreover, an attractive plant could also lower the number of visits to the less attractive plant, which is known as associational resistance. These associational effects have been commonly observed for pollinators visiting flowers and herbivorous insects feeding on different plant species. However, it is not fully understood how mixtures of different resources lead to different outcomes of associational effects.

    We tested how the density and frequency of different resources could lead to associational susceptibility or associational resistance using the common fruit fly, Drosophila melanogaster. Fruit flies are strongly attracted to fermenting fruits, which contain odours that are also found in balsamic vinegar. Therefore, we used balsamic vinegar to mimic food resources that differed in their attractiveness. With these resources we created patches containing different frequencies of attractive and less attractive resources.

    Firstly, we found that attractiveness of a resource patch depends on which resources it contains, but that there is threshold at which increasing the number of resources does not result in a higher attractiveness of the patch. Secondly, we found that fruit flies are always more attracted to the resource that smells most attractive in the patch. Because a higher number of flies visited the more attractive resource in the mixed patches, compared to when the more attractive resource occurred on its own, it experienced associational susceptibility. Moreover, the less attractive resource experienced associational resistance, as the number of fly visits was lower in mixed patches. The strength of this interaction increased with a decreasing frequency of the more attractive resource. These findings can have important implications for managing plants in mixed environments and can help to predict the relative numbers of insects visiting plants growing in the same area.

    Image caption: Photo credit: Sébastien Lebreton.
    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

    Who interacts with whom? A common framework for identifying linkage rules across different types of interactions

    Ignasi Bartomeus, Dominique Gravel, Jason M. Tylianakis, Marcelo A. Aizen, Ian A. Dickie and Maud Bernard-Verdier Eucera bee visiting Cistus salvifolius. Curro Molina.

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    To understand ecological communities of plants and animals, we need more than a list of species. We need to know how the species interact. In fact, most important ecological processes are mediated by an interaction. Take for instance a flowering plant and a bee. Only their interaction allows both bees and plants to reproduce. Other interactions involve predators and their prey, or herbivores and plants.

    We know that big fish eat small fish and that pollinators with long tongues tend to visit plants with deep flowers. However, quantifying who interacts with whom is not an easy task. For example, predators eat prey smaller than themselves, but not if the prey becomes too small for them. Similarly, pollinators with short tongues cannot reach deep flowers, but long-tongued pollinators may not be constrained to any type of flower.

    In this paper, we review recent advances in predicting interactions from species co-occurrence and develop a probabilistic model for inferring trait matching. We model the probability that two species interact based on the matching of their traits while taking into account species abundances. The model presented uses empirical data to understand why two species interact or not. We exemplify its use with three case studies, but the model can be applied to a great range of mutualistic and antagonistic interactions, from grasshoppers chewing on plant leaves to pollinators drinking nectar. Understanding the linkage rules is important to predict how the web of life is organized, especially in the face of the human-induced environmental changes we are experiencing.

    Image caption: Eucera bee visiting Cistus salvifolius. Curro Molina.
    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.

     

    Energy expenditure of adult green turtles at sea

    Manfred R. Enstipp, Katia Ballorain, Stéphane Ciccione, Tomoko Narazaki, Katsufumi Sato and Jean-Yves GeorgesAdult green turtle foraging at a seagrass meadow in Mayotte. Credit: Manfred Enstipp.

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    All living organisms must obtain food from the environment to provide energy for their daily lives. Understanding how much energy organisms need for their various activities is a central topic studied by eco-physiologists. In the case of marine turtles, knowing their energy needs during the different phases of their life at sea is essential for their conservation, which critically depends on successful reproduction. In these reptiles, reproduction is typically associated with long-distance migration and only occurs every few years. It is an enormous physical task and requires substantial energy reserves, which are build up at the foraging grounds. If a turtle has insufficient energy reserves, it will not be able to engage in costly reproduction, with consequences for population/conservation status.

    Using a novel technique (attaching small accelerometry dataloggers to turtles), we studied activity patterns and energy expenditure of adult green turtles foraging year-round at a seagrass meadow in Mayotte and during simulated migration (displacing a turtle from its nesting beach) off Mohéli, in the south-western Indian Ocean. We found a clearly structured activity pattern for turtles at the foraging site that persisted throughout the year. During daylight hours turtles foraged on the shallow seagrass meadow (many short/shallow dives), while at night they rested on the inner reef slope (few long/deep dives). Energy expenditure at the foraging site during the austral summer was low (~1.6 times the value at rest) and declined even further with decreasing water temperatures during the austral winter. By contrast, upon its oceanic release, the displaced turtle swam continuously towards its nesting beach, conducting shallow/short dives during the day, which, mostly at night, were interspersed with few deep/long dives. Energy expenditure during this simulated migration was greatly increased to ~3 times the value at rest, indicating the costliness of such undertaking. Using a novel technique, we were able to study the energy needs of adult green turtles in great detail and under natural conditions. We show that continuous feeding during daylight hours at their foraging site, at low energetic costs, allows these turtles to gradually build up energy reserves needed for migration and reproduction.

    Image caption: Adult green turtle foraging at a seagrass meadow in Mayotte. Credit: Manfred Enstipp.
    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.

     

    Author-suggested reviewers: Gender differences and influences on the peer review process at an ecology journal

    Charles Fox, C. Sean Burns, Anna Muncy and Jennifer MeyerImage from  “What is a journal and a peer reviewed article?” (Northeastern Illinois University Ronald Williams Library)

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    Peer review is the primary method by which journals evaluate the quality and importance of submitted manuscripts. Identifying suitable reviewers, and then recruiting them to review, is one of the most challenging parts of an editor’s job. Authors should know best who is qualified to review their papers; thus, to help editors find suitable reviewers, many journals allow or require authors to suggest names of preferred and non-preferred reviewers. However, authors also have a strong incentive to suggest reviewers that they expect to review their paper positively.

    In this study, we examine the reviewers that are suggested by authors as preferred (those that authors would like to review their manuscript) and non-preferred (those that authors request not be invited to review their paper), the use of these suggestions by editors, and their influence on the peer review process and outcomes at the journal Functional Ecology. We also examined how gender of the participants (author, editor and reviewer) influences the role of preferred reviewers in the peer review process.

    Most authors suggest preferred reviewers, but few suggest non-preferred reviewers. Most author-preferred reviewers are male, but the proportion of women among author suggestions increased from a low of 15% in 2004 to a high of 25% in 2014. Male and female authors did not differ in how likely they were to suggest preferred reviewers, but female authors suggest more female reviewers (~28%, averaged across years) than do male authors (~21%). Women that were suggested as preferred reviewers were more likely to be chosen by editors as desired reviewers than were men suggested by authors. We found no evidence that editor gender, seniority or length of service as an editor for Functional Ecology affected how likely they were to use author-suggested reviewers.

    Of reviewers invited to review, those that were suggested by authors were more likely to respond to the editors' review invitations but were not more likely to agree to review. Most strikingly, author-preferred reviewers rated papers much more positively than did editor-selected reviewers, and papers reviewed by author-preferred reviewers were much more likely to be invited for revision than were papers reviewed by editor-selected reviewers. This difference was not influenced by the gender of the participants in the process.

    Suggesting preferred reviewers clearly benefits authors – preferred reviewers rate papers significantly more positively (on average) than do editor-selected reviewers, improving the chances that a paper will be published. We thus recommend that authors always suggest preferred reviewers if given the option to do so by a journal. Journals and editors, by contrast, should consider who proposed the reviewer, and possible biases, when deciding whether to use author-suggested reviewers and when evaluating reviewer comments and scores. Highly-selective journals – those whose decisions emphasize broad general interest, significance and novelty – might consider eliminating the practice of allowing or requiring authors to suggest their own reviewers.

    Image caption: Image from “What is a journal and a peer reviewed article?” (Northeastern Illinois University Ronald Williams Library).
    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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