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Co-occurrence methods are increasingly utilized in ecology to infer networks of species interactions where detailed knowledge based on empirical studies is difficult to obtain. Their use is particularly common, but not restricted to, microbial networks constructed from metagenomic analyses. In this study, we test the efficacy of this procedure by comparing an inferred network constructed using spatially intensive co-occurrence data from the rocky intertidal zone in central Chile to a well-resolved, empirically based, species interaction network from the same region. We evaluated the overlap in the information provided by each network and the extent to which there is a bias for co-occurrence data to better detect known trophic or non-trophic, positive or negative interactions. We found a poor correspondence between the co-occurrence network and the known species interactions with overall sensitivity (probability of true link detection) equal to 0.469, and specificity (true non-interaction) equal to 0.527. The ability to detect interactions varied with interaction type. Positive non-trophic interactions such as commensalism and facilitation were detected at the highest rates. These results demonstrate that co-occurrence networks do not represent classical ecological networks in which interactions are defined by direct observations or experimental manipulations. Co-occurrence networks provide information about the joint spatial effects of environmental conditions, recruitment, and, to some extent, biotic interactions, and among the latter, they tend to better detect niche-expanding positive non-trophic interactions. Detection of links (sensitivity or specificity) was not higher for well-known intertidal keystone species than for the rest of consumers in the community. Thus, as observed in previous empirical and theoretical studies, patterns of interactions in co-occurrence networks must be interpreted with caution, especially when extending interaction-based ecological theory to interpret network variability and stability. Co-occurrence networks may be particularly valuable for analysis of community dynamics that blends interactions and environment, rather than pairwise interactions alone.

The very presence of predators can strongly influence flexible prey traits such as behavior, morphology, life history, and physiology. In a rapidly growing body of literature representing diverse ecological systems, these trait (or “fear”) responses have been shown to influence prey fitness components and density, and to have indirect effects on other species. However, this broad and exciting literature is burdened with inconsistent terminology that is likely hindering the development of inclusive frameworks and general advances in ecology. We examine the diverse terminology used in the literature, and discuss pros and cons of the many terms used. Common problems include the same term being used for different processes, and many different terms being used for the same process. To mitigate terminological barriers, we developed a conceptual framework that explicitly distinguishes the multiple predation-risk effects studied. These multiple effects, along with suggested standardized terminology, are risk-induced trait responses (i.e., effects on prey traits), interaction modifications (i.e., effects on prey–other-species interactions), nonconsumptive effects (i.e., effects on the fitness and density of the prey), and trait-mediated indirect effects (i.e., the effects on the fitness and density of other species). We apply the framework to three well studied systems to highlight how it can illuminate commonalities and differences among study systems. By clarifying and elucidating conceptually similar processes, the framework and standardized terminology can facilitate communication of insights and methodologies across systems and foster cross-disciplinary perspectives

Understanding the drivers of geographical variation in species distributions, and the resulting community structure, constitutes one of the grandest challenges in ecology. Geographical patterns of species richness and composition have been relatively well studied. Less is known about how the entire set of trophic and non-trophic ecological interactions, and the complex networks that they create by gluing species together in complex communities, change across geographical extents. Here, we compiled data of species composition and three types of ecological interactions occurring between species in rocky intertidal communities across a large spatial extent (~970 km of shoreline) of central Chile, and analyzed the geographical variability in these multiplex networks (i.e., comprising several interaction types) of ecological interactions. We calculated nine network summary statistics common across interaction types, and additional network attributes specific to each of the different types of interactions. We then investigated potential environmental drivers of this multivariate network organization. These included variation in sea surface temperature and coastal upwelling, the main drivers of productivity in nearshore waters. Our results suggest that structural properties of multiplex ecological networks are affected by local species richness and modulated by factors influencing productivity and environmental predictability. Our results show that non-trophic negative interactions are more sensitive to spatially structured temporal environmental variation than feeding relationships, with non-trophic positive interactions being the least labile to it. We also show that environmental effects are partly mediated through changes in species richness and partly through direct influences on species interactions, probably associated to changes in environmental predictability and to bottom-up nutrient availability. Our findings highlight the need for a comprehensive picture of ecological interactions and their geographical variability if we are to predict potential effects of environmental changes on ecological communities.

1. Domesticated plants can differ from their wild counterparts in the strength and outcome of species interactions, both above- and belowground. Plant-soil feedbacks influence plant success, and plant-associated soil microbial communities can influence plant interactions with herbivores and their natural enemies, yet, it remains unclear if domestication has changed these relationships. 2. To determine the effects of domestication on plant-soil interactions, we characterized soil microbial communities associated with various cultivars of domesticated tomato and some of its wild relatives. We measured the strength and direction of plant-soil feedbacks for domesticated and wild tomatoes, and the effects of soil on plant resistance to specialist herbivory by Manduca sexta, and the attraction of a parasitoid wasp, Cotesia congregata. 3. Domesticated tomatoes and their wild relatives had negative plant-soil feedbacks, as conspecifics cultivated soil that negatively impacted performance of subsequent plants (longer germination time, lower biomass) than if they grew in non-tomato soils. Significant variation existed among domesticated and wild tomato varieties in the strength of these feedbacks, ranging from neutral to strongly negative. For above-ground plant biomass, tomato wild relatives were unaffected by growing in tomato-conditioned soil, whereas domesticated tomatoes grew smaller in tomato soil, indicating effects of plant domestication. Overall, increased microbial biomass within the rhizosphere resulted in progressively less-negative plantsoil feedbacks. 4. Plant cultivars had different levels of resistance to herbivory by M. sexta, but this did not depend on plant domestication or soil type. The parasitoid C. congregata was primarily attracted to herbivore damaged plants, independent of plant domestication status, and for these damaged plants, wasps preferred some cultivars over others, and wild plants grown in tomato soil over wild plants grown in non-tomato soil. 5. Synthesis. These results indicate that crop tomatoes are more likely to show negative plant-soil feedbacks than wild progenitors, which could partially explain their sensitivity to monocultures in agricultural soils. Furthermore, cultivar-specific variation in the ability to generate soil microbial biomass, independent of domestication status, appears to buffer the negative consequences of sharing the same soil. Last, soil legacies were relatively absent for herbivores, but not for parasitoid wasps, suggesting trophic level specificity in soil feedbacks on plant-insect interactions.

Background For achieving long-term sustainability of intensive agricultural practices, it is pivotal to understand belowground functional stability as belowground organisms play essential roles in soil biogeochemical cycling. It is commonly believed that resource availability is critical for controlling the soil biodiversity and belowground organism interactions that ultimately lead to the stabilization or collapse of terrestrial ecosystem functions, but evidence to support this belief is still limited. Here, we leveraged field experiments from the Chinese National Ecosystem Research Network (CERN) and two microcosm experiments mimicking high and low resource conditions to explore how resource availability mediates soil biodiversity and potential multi-trophic interactions to control functional trait stability. Results We found that agricultural practice-induced higher resource availability increased potential cross-trophic interactions over 316% in fields, which in turn had a greater effect on functional trait stability, while low resource availability made the stability more dependent on the potential within trophic interactions and soil biodiversity. This large-scale pattern was confirmed by fine-scale microcosm systems, showing that microcosms with sufficient nutrient supply increase the proportion of potential cross-trophic interactions, which were positively associated with functional stability. Resource-driven belowground biodiversity and multi-trophic interactions ultimately feedback to the stability of plant biomass. Conclusions Our results indicated the importance of potential multi-trophic interactions in supporting belowground functional trait stability, especially when nutrients are sufficient, and also suggested the ecological benefits of fertilization programs in modern agricultural intensification. 6BT2faHzT3jQfWsk8Bso8N Video Abstract

How plant traits evolve along geographical and climatic gradients has recently received increased attention because of anticipated climate change and associated shifts in insect distribution, whether they are herbivores or predators. This issue is particularly relevant for traits related to growth and anti‐herbivore defence of plants, because both sets of traits are closely tied to fitness, and because being sessile organisms, plants tend to experience strong local selection. Despite widespread recognition that the abiotic environment imposes selection on plant traits, how temperature and water availability independently select for allocation to growth and defence against herbivores is not well‐resolved, and even more so, when considering under‐ground herbivory and tritrophic interactions involving plant herbivores and their predators. To address heritable, climate‐driven variation in root traits mediating tritrophic interactions, we performed a common garden experiment with four populations of common red fescue (Festuca rubra) encompassing the four corners of a precipitation by temperature gradient matrix. We found that plants originating from wetter and warmer conditions, in addition to producing more biomass, also produced a blend of volatile organic compounds more attractive for predatory nematodes of root insect herbivores. Moreover, across populations, variation in nematode attraction was mediated by balancing the emissions of attractive and repulsive volatile compounds. Our work builds towards better understanding how plant adaptation to climate interacts with adaptations to herbivores and their predators. A free Plain Language Summary can be found within the Supporting Information of this article. A free Plain Language Summary can be found within the Supporting Information of this article.

Polyploidy is a common mode of speciation that can have far-reaching consequences for plant ecology and evolution. Because polyploidy can induce an array of phenotypic changes, there can be cascading effects on interactions with other species. These interactions, in turn, can have reciprocal effects on polyploid plants, potentially impacting their establishment and persistence. Although there is a wealth of information on the genetic and phenotypic effects of polyploidy, the study of species interactions in polyploid plants remains a comparatively young field. Here we reviewed the available evidence for how polyploidy may impact many types of species interactions that range from mutualism to antagonism. Specifically, we focused on three main questions: (1) Does polyploidy directly cause the formation of novel interactions not experienced by diploids, or does it create an opportunity for natural selection to then form novel interactions? (2) Does polyploidy cause consistent, predictable changes in species interactions vs. the evolution of idiosyncratic differences? (3) Does polyploidy lead to greater evolvability in species interactions? From the scarce evidence available, we found that novel interactions are rare but that polyploidy can induce changes in pollinator, herbivore, and pathogen interactions. Although further tests are needed, it is likely that selection following whole-genome duplication is important in all types of species interaction and that there are circumstances in which polyploidy can enhance the evolvability of interactions with other species.

The relative roles of plants competing for resources versus top-down control of vegetation by herbivores, in turn impacted by predators, during early stages of tropical forest succession remain poorly understood. Here we examine the impact of insectivorous birds, bats, and ants exclusion on arthropods communities on replicated 5 × 5 m of pioneering early successional vegetation plots in lowland tropical forest gaps in Papua New Guinea. In plots from which focal taxa of predators were excluded we observed increased biomass of herbivorous and predatory arthropods, and increased density, and decreased diversity of herbivorous insects. However, changes in the biomass of plants, herbivores, and arthropod predators were positively correlated or uncorrelated between these three trophic levels and also between individual arthropod orders. Arthropod abundance and biomass correlated strongly with the plant biomass irrespective of the arthropods’ trophic position, a signal of bottom-up control. Patterns in herbivore specialization confirm lack of a strong top-down control and were largely unaffected by the exclusion of insectivorous birds, bats, and ants. No changes of plant–herbivore interaction networks were detected except for decrease in modularity of the exclosure plots. Our results suggest weak top-down control of herbivores, limited compensation between arthropod and vertebrate predators, and limited intra-guild predation by birds, bats, and ants. Possible explanations are strong bottom-up control, a low activity of the higher order predators, especially birds, possibly also bats, in gaps, and continuous influx of herbivores from surrounding mature forest matrix.

1. Habitat destruction, characterized by habitat loss and fragmentation, is a key driver of species extinction in spatial extended communities. Recently, there has been some progress in the theory of spatial food webs, however to date practically little is known about how habitat configurational fragmentation influences multi-trophic food web dynamics. 2. To explore how habitat fragmentation affects species persistence in food webs, we introduce a modelling framework that describes the site occupancy of species in a tri-trophic system. We assume that species dispersal range increases with trophic level, exploiting pair-approximation techniques to describe the effect of habitat clustering. 3. In accordance with the trophic rank hypothesis, both habitat loss and fragmentation generally cause species extinction, with stronger effects occurring at higher trophic levels. However, species display diverse responses (negative, neutral or positive) to habitat loss and fragmentation separately, depending on their dispersal range and trophic position. 4. Counter-intuitively, prey species may benefit from habitat loss due to a release in top-down control. Similarly, habitat fragmentation has almost no influence on the site occupancy of the intermediate consumer in the tri-trophic system, though it decreases those of both basal species and top predator. Consequently, species' responses to habitat destruction vary as other species become extinct. 5. Our results reiterate the importance of the interplay between bottom-up and top-down control in trophically linked communities, and highlight the complex responses occurring in even a simple food chain.

Foraging animals create nonrandom patterns of diversity and abundance within resource communities. Perceiving predation pressure and intraspecific competition for food resources, foragers can alter space use patterns, foraging intensity, and preference for specific functional traits of their resources. Consequently, variation in the behavior of foragers may alter the patterns of diversity in resource communities. We investigated the concurrent effects of predation risk to foragers, and of forager density on the diversity of resources in an experimental resource community. We created resource landscapes using experimental foraging patches in near‐natural rodent enclosures and replicated the experiment with two rodent species, which differed in their sociality and foraging ecology, so the importance of intraspecific competition could vary. For both species, predation risk (induced via open vs. covered foraging patches) led to reduced foraging activity (higher giving up densities). Consequently, resource diversity was higher in foraging patches and landscapes with greater perceived predation risk than in safe foraging patches and landscapes. Increased forager density in safe conditions decreased resource community diversity only in the less social species, which forages on depletable, ephemeral resources. Forager density had no effect under perceived predation risk. The more sociable species, which feeds on grasses that are not easily depletable, did not alter its foraging behavior with density. Our findings illustrate the overall importance of predation risk, not only on behavior but also on lower trophic levels, and that density effects are mediated by both predation risk and species ecology. Thus, predation, competition, and sociality at the consumer level can indirectly affect local and regional dynamics of communities of resource species.