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Toward a community ecology of landscapes: Predicting multiple predator-prey interactions across geographic space

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Abstract

Community ecology was traditionally an integrative science devoted to studying interactions between species and their abiotic environments in order to predict species' geographic distributions and abundances. Yet for philosophical and methodological reasons it has become divided into two enterprises: one devoted to local experimentation on species interactions to predict community dynamics; the other devoted to statistical analyses of abiotic and biotic information to describe geographic distribution. Our goal here is to instigate thinking about ways to reconnect the two enterprises and thereby return to a tradition to do integrative science. We focus specifically on the community ecology of predators and prey, which is ripe for integration. This is because there is active, simultaneous interest in experimentally resolving the nature and strength of predator-prey interactions as well as explaining pattern across landscapes and seascapes. We begin by describing a conceptual theory rooted in classical analyses of non-spatial food web modules used to predict species interactions. We show how such modules can be extended to consideration of spatial context using the concept of habitat domain. Habitat domain describes the spatial extent of habitat space that predators and prey use while foraging, which differs from home range, the spatial extent used by an animal to meet all of its daily needs. This conceptual theory can be used to predict how different spatial relations of predators and prey could lead to different emergent multiple predator-prey interactions such as whether predator consumptive or non-consumptive effects should dominate, and whether intraguild predation, predator interference or predator complementarity are expected. We then review the literature on studies of large predator-prey interactions that make conclusions about the nature of multiple predator-prey interactions. This analysis reveals that while many studies provide sufficient information about predator or prey spatial locations, and thus meet necessary conditions of the habitat domain conceptual theory for drawing conclusions about the nature of the predator-prey interactions, several studies do not. We therefore elaborate how modern technology and statistical approaches for animal movement analysis could be used to test the conceptual theory, using experimental or quasi-experimental analyses at landscape scales. This article is protected by copyright. All rights reserved.

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... grouping) and the environment (e.g. habitat structure) can influence the outcome of predator−prey interactions (Schmitz 2008, Creel 2011, Schmitz et al. 2017, Gaynor et al. 2019. By synthesizing these works in combination with an understanding of preda- ). ...
... Predicted attributes of sharks, prey and the environment leading to increases in the magnitude of shark top-down predation effects on prey, and whether consumptive effects (CE) or risk effects (RE) dominate these interactions. Predictions developed from synthesizing works of Schmitz (2008), Creel (2011, Schmitz et al. (2017), and Gaynor et al. (2019), in combination with an understanding of predator−prey interactions involving sharks based on my own experiences antipredatory responses in prey. These include schooling or grouping behavior, escape mode, space or time devoted to vigilance or refuge use, excursion distances and activity space (in 3 dimensions), foraging rates, body mass and condition, movement rate, stress levels, nutritional condition, and morphological structures associated with defense, detection, or evasion. ...
... In summary, relying on stomach contents and/or stable isotope signatures to assess the potential for sharks to initiate trophic cascades can be misleading and may significantly underestimate the strength of shark topdown predation effects on prey. A study approach that measures relevant functional attributes of sharks, prey and the environment can provide greater insights for quantifying the magnitude of top-down predation effects (Schmitz 2008, Creel 2011, Schmitz et al. 2017, Gaynor et al. 2019) and the potential for shark population declines or recoveries to trigger trophic cascades. As outlined by Ruppert et al. (2016), there is a need for research efforts to focus on predator−prey relations (rather than simply the ecology of the predator) to understand the process of predation. ...
Article
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Understanding the ecological impacts of sharks on prey populations has become a research priority given widespread shark population declines due to overfishing, combined with significant conservation efforts. Accordingly, many studies have conducted analyses of shark stomach contents and/or used biomarkers, such as stable isotope signatures, to assess dietary pat-terns in order to infer ecological roles. Here, I summarize how relying on stomach contents and/or stable isotope signatures to assess the potential for sharks to initiate trophic cascades can be misleading and may significantly underestimate the strength of shark top-down predation effects on prey. However, a study approach that measures attributes of the sharks (e.g. hunting mode), potential prey (e.g. escape speed) and the environment (e.g. habitat rugosity) can provide greater insights for quantifying the magnitude of top-down predation effects of sharks and the potential for their population declines or recoveries to trigger trophic cascades. To aid future investigations,I provide a set of predictions, based on ecological theory, which would specifically lead to increases in the magnitude of shark predation effects on prey populations. I also present key study approaches currently being employed by researchers to test such predictions.
... Foundational research on trophic ecology and lethal and risk effects has typically been associated with relatively small experimental systems featuring relatively small (e.g., < 1 kg) species (see Schmitz et al., 2017). Take for example the research on optimal foraging theory conducted by Werner and Mittelbach (1981) "in a small Michigan lake and an artificial pond" (p. ...
... Such standardization is important given that it is these systems with attacking carnivores and adept ungulate prey that present ideal candidates for research examining the nature and strength of risk effects Schmitz et al., 2017). Recent calls among the scientific community have questioned the extent to which research on risk effects in carnivore-ungulate systems adequately represents the complexity of these trophic systems (Cresswell and Quinn, 2013;LaManna and Martin, 2016;Moll et al., 2017;Say-Sallaz et al., this issue). ...
... Consequently, what is needed is studies from natural systems in which the complexity of multi-predator effects is assessed (Cresswell and Quinn, 2013;LaManna and Martin, 2016;Creel et al., 2017;Northfield et al., 2017). In the absence of multiple predatormultiple prey studies, it will be difficult to determine whether the underlying predator-prey frameworks are applicable (Peckarsky and McIntosh, 1998;Thaker et al., 2011;Dröge et al., 2017;Schmitz et al., 2017). ...
Article
Predation is a fundamental force exerting strong selective pressure on prey populations. Predators not only kill prey, triggering lethal effects, but also hunt prey which can induce risk effects. Foundational research has documented the importance of risk effects in predator-prey systems of arthropods, fish, birds, and rodents, among others. Risk effects research in carnivore-ungulate systems has expanded in the last 20 years. Presently, the degree to which this research mirrors the complexity of carnivore-ungulate trophic systems has been questioned. We synthesized this literature to quantify the tendency of risk effects research in carnivore-ungulate systems to be multispecies in design. Among the 170 studies that we reviewed, we found that on average just 1.26 (range = 1 to 5) carnivore species and 1.60 (range = 1 to 11) ungulate species were considered per study. Furthermore, 63% (n = 107 of 170) of the studies featured single predator - single prey research designs. These results contrast with the fact that all but one of the 82 carnivore-ungulate systems used this literature had multiple species of carnivores and/or ungulates. Thus, we detected a tendency to simplify complex systems. We relate these observations to the role of simplicity as: i) an underlying value of science (i.e., Occam's razor), ii) a cornerstone of predator-prey theory (e.g., Lotka-Volterra equations), and iii) part of the origins of risk effects research (i.e., experimental systems). Finally, we ground our discussion in the implications of this research for the conservation of carnivores and ungulates in the dynamic 21st century.
... Although the role of bottom-up factors in shaping species distributions has been intensively studied in recent decades (Elith and Leathwick, 2009;Guisan and Thuiller, 2005), we still know little about the importance of the biotic factors underlying most spatial patterns. Especially, the role of species interactions, within and across trophic levels, including those involving humans, remain largely unexplored (Darimont et al., 2015;Schmitz et al., 2017;Wiens, 2011;Worm and Paine, 2016). It has recently been proposed that community ecology should be 'rediscovered' as an integrative study of species interactions and spatial distributions (Schmitz et al., 2017), while accounting for direct and indirect anthropogenic effects on species distributions and behavior (Berger, 2007;Worm and Paine, 2016). ...
... Especially, the role of species interactions, within and across trophic levels, including those involving humans, remain largely unexplored (Darimont et al., 2015;Schmitz et al., 2017;Wiens, 2011;Worm and Paine, 2016). It has recently been proposed that community ecology should be 'rediscovered' as an integrative study of species interactions and spatial distributions (Schmitz et al., 2017), while accounting for direct and indirect anthropogenic effects on species distributions and behavior (Berger, 2007;Worm and Paine, 2016). ...
... Prey species react to the presence of large carnivores by adjusting their spatio-temporal patterns of landscape use (Creel et al., 2005;Kohl et al., 2018;Laundré et al., 2001;Valeix et al., 2009). These spatial interactions between trophic levels are usually context-dependent and are shaped by the biophysical characteristics of a landscape (Kauffman et al., 2007;Schmitz et al., 2017;Valeix et al., 2009). Many studies have addressed how carnivores affect their prey species, but these have generally used a single carnivore -single prey species approach, whereas many ecosystems host multiple carnivore and multiple prey species. ...
Article
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Large herbivores influence ecosystem functioning via their effects on vegetation at different spatial scales. It is often overlooked that the spatial distribution of large herbivores result from their responses to interacting top-down and bottom-up ecological gradients that create landscape-scale variation in the structure of the entire community. We studied the complexity of these cascading interactions using high-resolution camera trapping and remote sensing data in the best-preserved European lowland forest, Białowieża Forest, Poland. We showed that the variation in spatial distribution of an entire community of large herbivores is explained by species-specific responses to both environmental bottom-up and biotic top-down factors in combination with human-induced (cascading) effects. We decomposed the spatial variation in herbivore community structure and identified functionally distinct landscape-scale herbivory regimes ('herbiscapes') which are predicted to occur in a variety of ecosystems and could be an important mechanism creating spatial variation in herbivory maintaining vegetation heterogeneity.
... In the meta-ecosystem conception, trophic interactions within ecosystem determine nutrient uptake and assimilation by herbivores and carnivores ( Fig. 1), while habitat structure within an ecosystem largely influences species spatial occurrences and the nature of their interactions (Leroux & Loreau, 2008;Schmitz et al., 2017;. Thus, an accounting of animal spatial interactions will require specifying (1) the spatial extent and spatial grain size to analyze the focal animal species and their interdependent predators or prey (i.e., the spatial structure of the food chain) in relation to ...
... Habitat domain describes the spatial extent of landscape space over which individual herbivores and carnivores roam while foraging for energy and nutrients. It offers a way to relate landscape habitat features with the spatial relations of predators and prey and how those spatial relations determine the nature of their interactions, including avoiding being preyed-upon (Schmitz et al., 2017). Habitat domain can include local movement while foraging and migratory movement to new foraging sites. ...
... This is especially relevant for aligning animal movement data with dynamic habitat and static topographic landscape features because animal movement is typically measured at finer spatio-temporal resolutions than is remotely sensed imagery (Remelgado et al., 2017;2019). The habitat domain can be measured using movement data from tracked individuals across a landscape, to calculate an animal's utilization distribution and probabilities of spatial locations associated with foraging and migration behaviour across a landscape (Schmitz et al., 2017). ...
Article
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1. Energy, nutrients, and organisms move over landscapes, connecting ecosystems across space and time. Meta-ecosystem theory investigates the emerging properties of local ecosystems coupled spatially by these movements of organisms and matter, by explicitly tracking exchanges of multiple substances across ecosystem borders. To date, meta-ecosystem research has focused mostly on abiotic flows - neglecting biotic nutrient flows. However, recent work has indicated animals act as spatial nutrient vectors when they transport nutrients across landscapes in the form of excreta, egesta, and their own bodies. 2. Partly due to its high level of abstraction, there are few empirical tests of meta-ecosystem theory. Further, while animals may be viewed as important mediators of ecosystem functions, better integration of tools is needed to develop predictive insights of their relative roles and impacts on diverse ecosystems. We present a methodological roadmap that explains how to do such integration by discussing how to combine insights from movement, foraging, and ecosystem ecology to develop a coherent understanding of animal-vectored nutrient transport on meta-ecosystems processes. 3. We discuss how the slate of newly-developed technologies and methods - tracking devices, mechanistic movement models, diet reconstruction techniques and remote sensing - that when integrated have the potential to advance the quantification of animal-vectored nutrient flows and increase the predictive power of meta-ecosystem theory. 4. We demonstrate that by integrating novel and established tools of animal ecology, ecosystem ecology, and remote sensing, we can begin to identify and quantify animal-mediated nutrient translocation by large animals. We also provide conceptual examples that show how our proposed integration of methodologies can help investigate ecosystem impacts of large animal movement. We conclude by describing practical advancements to understanding cross-ecosystem contributions of animals on the move. 5. Understanding the mechanisms by which animals shape ecosystem dynamics is important for ongoing conservation, rewilding, and restoration initiatives around the world, and for developing more accurate models of ecosystem nutrient budgets. Our road map will enable ecologists to better qualify and quantify animal mediated nutrient translocation for animals on the move. Graphical Abstract text: Incorporation of animal subsidies into biogeochemical budgets has been hampered by large degree of abstraction and little overview on disparate fields necessary to 'animate' ecosystem budgets. The authors provide a methodological road map to aid the design and implementation of these studies, demonstrating the power of integrating tools from all three fields.
... Meanwhile, prey should avoid roaming predators (e.g. coyotes and bears), which actively search for prey across an area (Bastille-Rousseau et al., 2016), by decreasing their temporal overlap (Schmitz et al., 2017). Because bears and coyotes tend to be active at different times (Bridges et al., 2004 lates becoming harder to catch as they grow older; Rayl et al., 2018). ...
... Fawn temporal overlap with coyotes also increased, but only after July 26. This increase in temporal overlap coincided with spatiotemporal avoidance of the same, suggesting fawns traded temporal avoidance of coyotes, as would be expected with a roaming predator (Schmitz et al., 2017), with finer-scale avoidance of the same. ...
... Although fawns used a combination of spatiotemporal avoidance and vigilance to avoid predation, in their attempt to avoid one predator, they might have made themselves vulnerable to another (Leblond et al., 2016). Fawns spatially avoiding an ambush predator like bobcats on a fine temporal scale would be more efficient than avoiding them completely or shifting their activity patterns and subsequently increasing their temporal overlap with other predators (Schmitz et al., 2017). However, fawns only avoided bobcats at this fine scale in the forest matrix site; they did not avoid them in the agriculture-development matrix sites, possibly due to lower occurrence of bobcats in these sites (Murphy, 2021). ...
Article
Perceived predation risk and the resulting antipredator behaviour varies across space, time and predator identity. Communities with multiple predators that interact and differ in their use of space, time of activity and hunting mode create a complex landscape for prey to avoid predation. Anthropogenic presence and disturbance have the potential to shift interactions among predators and prey and the where and when encounters occur. We examined how white-tailed deer Odocoileus virginianus fawn spatiotemporal antipredator behaviour differed along an anthropogenic disturbance gradient that had black bears Ursus americanus, coyotes Canis latrans, bobcats Lynx rufus and humans present. We quantified (a) spatial co-occurrence in species distributions, (b) temporal overlap across the diel cycle and (c) spatiotemporal associations between humans, bears, coyotes, bobcats, adult male deer and fawns. We also examined how deer vigilance behaviour changed across the anthropogenic disturbance gradient and survey duration. Anthropogenic disturbance influenced spatiotemporal co-occurrence across multiple scales, often increasing spatiotemporal overlap among species. In general, species' spatial co-occurrence was neutral or positive in anthropogenically disturbed environments. Bears and fawns, coyotes and adult male deer, and bobcats and fawns all had higher temporal overlap in the agriculture-development matrix sites. In addition, factors that influenced deer vigilance (e.g. distance to forest edge and predator relative abundance) in the agriculture-development matrix sites did not in the forest matrix site. By taking into account the different antipredator behaviours that can be detected and the different scales these behaviours might occur, we were able to gain a more comprehensive picture of how humans reduce available niche space for wildlife, creating the neutral and positive spatiotemporal associations between species that studies have been seeing in more disturbed areas.
... Yet fear effects may not always be the predominant driver of predator-prey interactions (Schmitz et al., 2004;Middleton et al., 2013;Moll et al., 2016;Bleicher, 2017;Schmitz et al., 2017;Peers et al., 2018). Theory predicts that the predominance of non-consumptive fear effects (as opposed to consumptive predation effects) will be contextdependent, as determined by the nature of predator and prey spatial associations and movements ( Fig. 1; Schmitz et al., 2004Schmitz et al., , 2017. ...
... Yet fear effects may not always be the predominant driver of predator-prey interactions (Schmitz et al., 2004;Middleton et al., 2013;Moll et al., 2016;Bleicher, 2017;Schmitz et al., 2017;Peers et al., 2018). Theory predicts that the predominance of non-consumptive fear effects (as opposed to consumptive predation effects) will be contextdependent, as determined by the nature of predator and prey spatial associations and movements ( Fig. 1; Schmitz et al., 2004Schmitz et al., , 2017. This prediction has been supported empirically in studies of wild prey species (Valeix et al., 2009;Thaker et al., 2011;Middleton et al., 2013;Miller et al., 2014;Basille et al., 2015;Moll et al., 2016). ...
... (Adapted from Fig. 1 in Schmitz et al. (2017).) predation, prey forego foraging and act to avoid being consumed (Schmitz et al., 2017). ...
Article
In recent decades the ‘landscape of fear’ has grown in popularity to become a central consideration in wildlife management, and has even been reconceptualized as the ‘landscape of coexistence’ for understanding human-wildlife conflicts such as predator attacks on livestock. Yet fear effects are not always the predominant driver of predator-prey interactions. Thus, guiding ecological principles have not been assembled to explain the broader food web interactions that shape the context dependency of carnivore-livestock conflict. We address this gap by developing a conceptual framework as a way to think about the contingencies under which inducing non-consumptive ‘fear effects’ on predators would be effective to mitigate carnivore-livestock conflict. The framework specifically considers interactions among wildlife (carnivore predators, wild ungulate prey) and humans (people and livestock) in terms of spatial predator-prey assemblages in which the nature of wildlife-human interactions – as either a carnivore-livestock conflict or a coexistence food web – is contingent on the nature of spatial movement and overlap of humans and wildlife across landscapes. Considering human-wildlife interactions within such a spatial food web context can assist in enabling people and wildlife, especially imperiled carnivores, to coexist in human-modified landscapes. The framework offers predictions that should be tested via adaptive management experiments that evaluate whether conflict mitigation solutions aligned with particular spatial human-livestock-carnivore contexts do indeed resolve conflict.
... The response race may be strongly influenced by predator hunting mode and habitat distribution, because these factors can mediate the hunting capacity of the predator and the ability of prey to detect, escape, or avoid predators (Schmitz et al. 2004(Schmitz et al. , 2017. When predators are confined to a narrow habitat domain to hunt successfully, prey can readily avoid them, resulting in strong spatial antipredator behavior (Hugie and Dill 1994, Heithaus 2001, Schmitz et al. 2017. ...
... The response race may be strongly influenced by predator hunting mode and habitat distribution, because these factors can mediate the hunting capacity of the predator and the ability of prey to detect, escape, or avoid predators (Schmitz et al. 2004(Schmitz et al. , 2017. When predators are confined to a narrow habitat domain to hunt successfully, prey can readily avoid them, resulting in strong spatial antipredator behavior (Hugie and Dill 1994, Heithaus 2001, Schmitz et al. 2017. Any limitation on predator hunting conditions (i.e., required stalking cover) allows prey to mitigate their predation risk by utilizing areas where predator hunting efficacy is diminished (Sih 1984, Cresswell et al. 2010, Schmitz et al. 2017. ...
... When predators are confined to a narrow habitat domain to hunt successfully, prey can readily avoid them, resulting in strong spatial antipredator behavior (Hugie and Dill 1994, Heithaus 2001, Schmitz et al. 2017. Any limitation on predator hunting conditions (i.e., required stalking cover) allows prey to mitigate their predation risk by utilizing areas where predator hunting efficacy is diminished (Sih 1984, Cresswell et al. 2010, Schmitz et al. 2017. However, when prey depend on a limited and patchy food resource they may be forced to endure higher spatial overlap with predators, as predators are able to readily predict prey location (Sih 2005). ...
Article
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The spatial relationship between predator and prey is often conceptualized as a behavioral response race, in which prey avoid predators while predators track prey. Limiting habitat types can create spatial anchors for prey or predators, influencing the likelihood that the predator or prey response will dominate. Joint spatial anchors emerge when predator and prey occupy similar feeding habitat domains and risk and reward become spatially conflated, confusing predictions of which player will win the space race. These spatial dynamics of risk‐foraging trade‐offs are often obscured by habitat heterogeneity and community complexity in large vertebrate systems, fueling ambiguity regarding the generality of predictions from predator–prey theory. To test how habitat distribution influences the predator–prey space race, we examine correlation in puma and vicuña habitat selection and space use at two sites, one of which generates a distinct risk–foraging trade‐off at a joint spatial anchor. The distribution of vegetation, which serves as both forage for vicuñas and stalking cover for pumas, differs between the sites; the llano contains a single central meadow that acts as a joint spatial anchor, while the canyon is characterized by more heterogeneous vegetation. Puma–vicuña habitat selection correlation was positive in the llano and negative in the canyon, and similarly, utilization distributions were more strongly correlated in the llano than the canyon. Vicuña locations occurred at higher values of puma habitat selection and utilization in the llano than in the canyon. Similarly, puma locations in the llano occurred at higher values of vicuña habitat selection and utilization than in the canyon. Although pumas consistently selected for and utilized vegetative and topographic cover regardless of habitat distribution, vicuñas only selected against vegetation in the heterogeneous canyon site, reducing spatial correlation with pumas. Our work suggests a joint spatial anchor favors pumas in the space race due to the inability for vicuñas to avoid crucial foraging habitat. The outcome of the predator–prey space race appears to be strongly informed by the distribution of habitat, whereby corresponding predictability of predator and prey favors predators in the spatial game.
... These indirect cues of predation risk culminate in the "landscape of fear" (Laundre et al. 2010) and often influence space-use more broadly (Janssen et al. 2007;Laundre et al. 2010). Predators that exhibit a narrow habitat domain, with a preference for specific habitat characteristics, have been found to influence space-use more strongly (Schmitz 2008), causing the prey to spatially or temporally avoid those areas (Schmitz et al. 2017;Smith et al. 2019). Because indirect cues of risk provide less accurate information on the identity and state of potential risk, the costs of false-positive (missed opportunity costs) and false-negative errors (potential death) will generally lead species to become more wary (i.e., cause species to perceive a higher level of risk than is actually present ;Sih 1992;Lima and Bednekoff 1999). ...
... The observed differences in habitat use between competing carnivores might be attributed to hunting strategies (Broekhuis et al. 2013) or resource availability (Rosenheim 2004). However, subordinate carnivores can minimize negative encounters by avoiding the habitat features associated with their predators (Heithaus 2001;Schmitz 2008), especially if the predators have a narrow habitat domain (Schmitz et al. 2017). Although culpeo and chilla fox co-occurrence was mediated by open habitat, pumas strongly influenced the space-use of both species. ...
... Direct and indirect cues of predation risk are often subtle and difficult to detect by prey (Guiden et al. 2019). Indirect cues like habitat type are particularly important if they offer an honest signal of space use, which is the case for species with a narrow habitat domain (Schmitz et al. 2017). However, the coupling between perceived and actual risk can break down due to the large fitness cost of predation, leading to some species showing a tendency to perceive a higher probability of predation than is actually present, and to "play it safe" (Abrams 1994). ...
Article
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Competition structures ecological communities. In carnivorans, competitive interactions are disproportionately costly to subordinate carnivores who must account for the risk of interspecific killing when foraging. Accordingly, missed opportunity costs for meso-carnivores imposed by risk can benefit the smallest-bodied competitors. However, the extent to which the risk perpetuates into spatial partitioning in hierarchically structured communities remains unknown. To determine how risk-avoidance behaviors shape the space-use of carnivore communities, we studied a simple community of carnivores in northern Patagonia, Argentina: pumas (Puma concolor; an apex carnivore), culpeo foxes (Lycalopex culpaeus; a meso-carnivore), and chilla foxes (Lycalopex griseus; a small carnivore). We used multi-species occupancy models to quantify the space use within the carnivore community and giving-up densities to understand the behaviors that structure space use. Notably, we applied an analytical framework that tests whether the actual or perceived risk of predation most strongly influences the space use of subordinate carnivores although accounting for their foraging and vigilance behaviors. We found that there was a dominance hierarchy from the apex carnivore through the meso-carnivore to the subordinate small carnivore, which was reflected in space. Although both meso- and small carnivores exhibited similar predator avoidance behavioral responses to apex carnivores, the habitat associations of apex carnivores only altered meso-carnivore space use. The biases in risk management we observed for meso-carnivores likely translates into stable co-existence of this community of competing carnivores. We believe our analytical framework can be extended to other communities to quantify the spatial-behavioral tradeoffs of risk.
... Given these complexities, studies of predator-prey interactions have often used proxies for the risk of predation that can be readily measured in field situations with mobile or cryptic animals (Moll et al. 2017, Prugh et al. 2019. Spatial overlap between predators and prey has emerged as a common metric (Schmitz et al. 2017), being both a necessary prerequisite to any predation event and relatively easy to calculate from available data sources such as predator and prey surveys or GPS locations. However, the degree to which spatial overlap serves as a valid proxy for predation risk rests on a series of assumptions that have often been overlooked and unvalidated in predator-prey research, particularly research involving medium-to largebodied vertebrates. ...
... Predator locomotion and hunting modes (e.g. sit-wait versus active search) have significant effects on how predators and their prey are predicted to use space (Schmitz et al. 2017), but the general assumption has been that predators should try to increase their overlap with prey while prey should try to minimize overlap in what is often called the 'predator-prey space race' (Sih 1984, Hugie andDill 1994). The focus on spatial overlap as a proxy for predator-prey interactions, particularly in free-ranging animals, has been driven in large part by past practicalities (e.g. ...
... This scenario may occur if predator and prey have narrow and opposing habitat domains (i.e. feeding ranges) within large areas of shared space use (Schmitz et al. 2017). Analyses can account for issues of scale by calculating overlap not for the overall home range, but for home range centers (e.g. ...
Article
Predation risk, the probability that a prey animal will be killed by a predator, is fundamental to theoretical and applied ecology. Predation risk varies with animal behavior and environmental conditions, yet attempts to understand predation risk in natural systems often ignore important ecological and environmental complexities, relying instead on proxies for actual risk such as predator–prey spatial overlap. Here we detail the ecological and environmental complexities driving disconnects between three stages of the predation sequence that are often assumed to be tightly linked: spatial overlap, encounters and prey capture. Our review highlights several major sources of variability in natural predator–prey systems that lead to the decoupling of spatial overlap estimates from actual encounter rates (e.g. temporal activity patterns, predator and prey movement capacity, resource limitations) and that affect the probability of prey capture given encounter (e.g. predator hunger levels, temporal, topographic and other environmental influences on capture success). Emerging technologies and statistical methods are facilitating a transition to a more spatiotemporally detailed, mechanistic understanding of predator–prey interactions, allowing for the concurrent examination of multiple stages of the predation sequence in mobile, free‐ranging animals. We describe crucial applications of this new understanding to fundamental and applied ecology, highlighting opportunities to better integrate ecological contingencies into dynamic predator–prey models and to harness a mechanistic understanding of predator–prey interactions to improve targeting and effectiveness of conservation interventions.
... Patterns of niche overlap across multiple dimensions may thus be predictive of MPEs in ecosystems and of indirect interactions between predators (Schmitz et al. 2017). The conservation implications, for predators and for prey, of these various scenarios are altogether divergent. ...
... Despite their relevance to conservation and ecology, intraguild interactions among carnivores are difficult to observe and quantify. Accordingly, investigators typically rely on more observable patterns of niche overlap and partitioning to characterize and anticipate potential interactions within predator guilds (Schmitz et al. 2017), even if the realized nature and strength of those interactions is expected to shift with varying conditions and resource levels . In light of ongoing global losses of intact large carnivore guilds and prey communities (Wolf andRipple 2016, 2017), and the role of anthropogenic disturbance as a mediator of intraguild interactions (Mannick and Pauli 2020; Seveque et al. 2020), assessing patterns of niche partitioning is critical to large-carnivore conservation planning (Lahkar et al. 2020). ...
... Namely, if prey availability is limiting, high dietary overlap may indicate strong exploitation competition (and, by extension, interference competition), but if not, dietary overlap may be detached from competition . Alternatively, high dietary overlap among predators with low spatial ) but high temporal (Kohl et al. 2019) overlap could reflect predator facilitation (Kotler and Brown 1992), but (again) only if prey are a limiting factor, and only if prey move freely between predator domains (Schmitz et al. 2017 Here, we investigate patterns of dietary, spatial, and temporal overlap and partitioning between sympatric snow leopards (Panthera uncia) and wolves (Canis lupus) in a shared landscape managed for both seasonal pastoralist livestock grazing and wildlife conservation in the high mountains of Central Asia. At large scales, snow leopards are sympatric with wolves throughout the range of the former, often with substantial overlap in their reliance on large ungulate prey, leading investigators to infer the potential for exploitation competition (Jumabay-Uulu et al. 2013;Bocci et al. 2017;Chetri et al. 2017). ...
Thesis
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Predators shape their ecosystems through myriad interactions with prey, other predators, and humans. However, the effects of these interactions may be contingent on multiple contextual factors, hindering prediction in any given community and impeding a general understanding of the ecological effects of predators. Despite their prominence as conservation flagship in the mountains of Central Asia, even basic aspects of snow leopard (Panthera uncia) ecology remain underexplored and poorly understood. The ecology of wolves (Canis lupus), sympatric with snow leopards throughout that species’ range, has been even more neglected in the region, notwithstanding the significant impact of livestock depredation on pastoralist communities. This dissertation examines the interactions underlying the coexistence of wolves and snow leopards, including those with humans and their joint effects on prey, with the broader goal of improving our understanding of the context-dependence of the non-consumptive effects (NCEs) of predators. In Chapter 2, I explore the patterns of spatial, temporal, and dietary niche overlap between wolves and snow leopards in the Eastern Pamir Mountains of Tajikistan. I show that in iv light of dietary and temporal overlap, the two predators’ coexistence may depend on strong spatial partitioning. In Chapter 3, I explore the consequences of this spatial partitioning by investigating how shared prey with distinct escape tactics, ibex (Capra sibirica) and argali (Ovis ammon), navigate the tradeoffs posed by the two predators in the Central Tien Shan Mountains of Kyrgyzstan. Each ungulate responded to each predator in a manner that was predictable based on the compatibility of their respective evasion and hunting-mode traits, suggesting that nonconsumptive predator effects depend not on predator hunting mode or prey escape tactics, but rather on their interaction. Furthermore, short-term predation risk may upend each ungulates’ long-term risk avoidance strategy, suggesting that emergent effects of multiple predators may have important consequences in this system. In Chapter 4, I develop a novel approach to investigate large-scale patterns of livestock depredation risk and occurrence for wolves and snow leopards, but also lynx (Lynx lynx) and bears (Ursus arctos), in the Western Pamirs of Tajikistan. Livestock depredation was commonplace, with most communities exposed to multiple predators, highlighting that conservation efforts meant to reduce conflict between people and carnivores should aim to reduce depredation as it is experienced by human communities – a threat from the entire carnivore guild. Overall, my results suggest that single-species approaches to conservation in the mountains of Central Asia may be inadequate for ecosystems and people. This dissertation advances the cause of conservation in Central Asia by providing an empirical perspective on how snow leopards and wolves coexist and shape their ecosystems, and by providing practical insight into the challenge of livestock depredation and conflict, a primary threat to wolves and snow leopards in the region. By showing that the non-consumptive effects of predators cannot be predicted based solely on prey escape tactics or predator hunting mode alone, it also contributes to a more comprehensive understanding of the role of predators in shaping ecosystems.
... Both predator and prey can be studied using optimal foraging theory, which paints a dynamic picture as it predicts how individuals strive for the optimal balance between fitness gains from feeding versus potential fitness losses from exposure to predators (Lima andDill 1990, Schmitz et al. 2004). Tradeoffs between feeding and exposure to predators can cause strong and diverse indirect effects on entire ecosystems, through changes in behaviour or habitat choice (Schmitz 2010, Schmitz et al. 2017, morphology (Grant and Bayly 1981), and other phenotypic traits (Preisser et al. 2005, Schmitz 2010. When predation risk influences fitness correlates (e.g. ...
... While most predator-prey theory assumes that all predator species act the same and elicit qualitatively similar antipredator behavioural responses in their prey, the nature and strength of non-consumptive effects may vary with the predator's presence and abundance, its hunting mode and its habitat use (Schmitz 2010, Schmitz et al. 2017. Typical responses of prey to the presence of a predator include hiding more, moving less and changing habitats (Sih 1992, Peckarsky 1996, Stoks et al. 2003, Miller et al. 2014. ...
... Although these species are competitors for the same prey, certain individuals have been observed to cooperate during hunting, with the moray searching inside the reef and the grouper waiting just outside, leaving prey with no alternative for escape. Similar behaviours, or more simply a spatial affinity between predators having complementary detection or capture modes, may have implications for survival of prey and can drive more elusive patterns of predator-prey and predator-predator interactions (Schmitz et al. 2017). ...
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Prey modify their behaviour to avoid predation, but dilemmas arise when predators vary in hunting style. Behaviours that successfully evade one predator sometimes facilitate exposure to another predator, forcing the prey to choose the lesser of two evils. In such cases, we need to quantify behavioural strategies in a mix of predators. We model optimal behaviour of Atlantic cod Gadus morhua larvae in a water column, and find the minimal vulnerability from three common predator groups with different hunting modes; i) ambush predators that sit‐and‐wait for approaching fish larvae; ii) cruising invertebrates that eat larvae in their path; and iii) fish which are visually hunting predators. We use a state‐dependent model to find optimal behaviours (vertical position and swimming speed over a diel light cycle) under any given exposure to the three distinct modes of predation. We then vary abundance of each predator and quantify direct and indirect effects of predation. The nature and strength of direct and indirect effects varied with predator type and abundance. Larvae escaped about half the mortality from fish by swimming deeper to avoid light, but their activity level and cumulative predation from ambush predators increased. When ambush invertebrates dominated, it was optimal to be less active but in more lit habitats, and predation from fish increased. Against cruising predators, there was no remedy. In all cases, the shift in behaviour allowed growth to remain almost the same, while total predation were cut by one third. In early life stages with high and size‐dependent mortality rates, growth rate can be a poor measure of the importance of behavioural strategies. This article is protected by copyright. All rights reserved.
... However, prey naivete frameworks (e.g. [4]) rarely incorporate the ecology and behaviour of alien predators, despite evidence that these affect the rate and outcomes of predator-prey interactions [5][6][7]. Figure 1 presents a framework to evaluate the mechanisms underpinning differences in the impact of novel versus familiar predators. In addition to classes of the prey response [3,4], it incorporates elements of predator ecology (following Sih et al. [8]), synthesizing existing frameworks into a format that can readily be applied to empirical data to make or test predictions. ...
... Whereas CEs only occur during the physical encounter with the predator, NCEs are also incurred by responding to cues which are spatially and temporally separated from the predator (e.g. scent and vocalizations) [6]. The magnitude of NCEs incurred in each encounter will be determined by the nature of prey response. ...
... Hunting mode (usually categorized as 'active hunting', 'sit-and-pursue' or 'sit-and-wait') determines the degree of association between the predator and cues to its presence, and therefore how reliably these cues indicate encounter risk [5,6,11]. This in turn should influence how likely prey are to employ anti-predator responses and incur NCEs [11]. ...
Article
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Alien mammalian carnivores have contributed disproportionately to global loss of biodiversity. In Australia, predation by the feral cat and red fox is one of the most significant causes of the decline of native vertebrates. To discover why cats have greater impacts on prey than native predators, we compared the ecology of the feral cat to a marsupial counterpart, the spotted-tailed quoll. Individual prey are 20–200 times more likely to encounter feral cats, because of the combined effects of cats' higher population densities, greater intensity of home-range use and broader habitat preferences. These characteristics also mean that the costs to the prey of adopting anti-predator behaviours against feral cats are likely to be much higher than adopting such behaviours in response to spotted-tailed quolls, due to the reliability and ubiquity of feral cat cues. These results help explain the devastating impacts of cats on wildlife in Australia and other parts of the world.
... Each hunting mode has adaptively evolved via some combination of predator and prey behavior and life history characteristics, animal-habitat relationships, and previous predator-prey interactions (Carey and Wahl, 2011;Belgrad and Griffen, 2016). The spatio-temporal patterns of predator cues vary according to each hunting mode with consequences for the nature and strength of the consumptive and NCEs of predation in the habitat domains within which these predator-prey interactions take place (Schmitz, 2005;Preisser et al., 2007;Miller et al., 2014;Northfield et al., 2017;Schmitz et al., 2017). Given the veritable arms race that loosely describes predator-prey interactions (Dawkins and Krebs, 1979;Sih, 1984Sih, , 2005, the costs and benefits of these different hunting modes lie at the very heart of the evolution of behavior for both predators and prey (Krebs and Davies, 2009;Lima and Dill, 1990). ...
... Thus, the cues of predation are integral to the anti-predator behavioral responses of prey (Relyea, 2003;Sih et al., 2010). These behavioral responses are suggested to be strongest in relation to sit-and-wait predators, where predation risk is imminent, intermediate in relation to sitand-pursue predators, and weakest in relation to active predators (Preisser et al., 2007;Schmitz et al., 2017). Within this context, the combination of predator hunting mode and habitat domain width (determined by the space use of the subject animals) facilitate predictions of the nature and strength of NCEs with subsequent implications for ecosystem structure via the potential cascading effects of predation (Schmitz, 2005;Miller et al., 2014;Northfield et al., 2017). ...
Article
When seeking prey, predators adaptively deploy strategies coarsely divided into sit-and-wait, sit-and-pursue, or active hunting modes. Though the hunting modes of many predators have been extensively studied, the implications of the hunting modes of human (Homo sapiens) predation are not yet fully understood. We conducted an extensive literature review to document human hunting modes and explore the ways in which these modes may shape animal populations via nonconsumptive effects (NCEs) of human predation. Among 169 studies published between 1972 and 2020, we found that humans used 27 hunting tools among 19 different hunting techniques when pursuing terrestrial prey. Most accounts described humans as using the active hunting mode (58%; n = 139 of 241), followed by the sit-and-wait hunting mode (41%; n = 98 of 241), and finally the sit-and-pursue hunting mode (2%; n = 4 of 241). While non-human predators tend to be evolutionarily adapted to the use of just one hunting mode, humans showed profound plasticity by deploying all three hunting modes in pursuit of prey species from 34 taxonomic orders spanning six orders of magnitude in body size (from 27 g to 4400 kg). Considerable evidence has documented the vast number of ways in which humans directly impact the functioning of the natural world. Our research complements that work by demonstrating the indirect pathways by which humans may affect animal populations and the landscapes over which these interactions occur, via NCEs deriving from the hunting modes of human predation, with important implications for animal conservation.
... Despite their relevance to conservation and ecology, intraguild interactions among carnivores are difficult to observe and quantify. Accordingly, investigators typically rely on more observable patterns of niche overlap and partitioning to characterize and anticipate potential interactions within predator guilds (Schmitz et al. 2017), even if the realized nature and strength of those interactions are expected to shift with varying conditions and resource levels (Wiens 1993). In light of ongoing global losses of intact large carnivore guilds and prey communities Ripple 2016, 2017), and the role of anthropogenic disturbance as a mediator of intraguild interactions (Manlick and Pauli 2020;Sévêque et al. 2020), assessing patterns of niche partitioning is critical to large carnivore conservation planning (Lahkar et al. 2020). ...
... Namely, if prey availability is limiting, high dietary overlap may indicate strong exploitation competition (and, by extension, interference competition), but if not, dietary overlap may be detached from competition (Wiens 1993). Alternatively, high dietary overlap among predators with low spatial (Sih et al. 1998) but high temporal (Kohl et al. 2019) overlap could reflect predator facilitation (Kotler et al. 1992), but (again) only if prey are a limiting factor, and only if prey move freely between predator domains (Schmitz et al. 2017). Given the divergent conservation implications of predator facilitation and competition, there is a clear need to consider multiple niche dimensions in parallel, particularly where humans have restructured ecological communities. ...
Article
Direct and indirect interactions among predators affect predator fitness, distribution, and overall community structure. Yet, outside of experimental settings, such interactions are difficult to observe and thus poorly understood. Patterns of niche overlap among predators reflect and shape community interactions and may therefore help elucidate the nature and intensity of intraguild interactions. To better understand the coexistence of two apex predators, snow leopards (Panthera uncia) and wolves (Canis lupus), we investigated their spatial, temporal, and dietary niche overlap in summer in the Pamir Mountains of Tajikistan. We estimated population-level space use via spatial capture-recapture models based on noninvasive genetics and camera traps, diel activity patterns based on camera trap detections, and diet composition from prey remains in carnivore scats, from which we estimated coefficients between 0 and 1 for overlap in space, time, and diet, respectively. Snow leopards and wolves displayed moderate spatial partitioning (0.26, 95% confidence interval [CI]: 0.17-37), but overlapping temporal (0.77, 95% CI: 0.64-0.90) and dietary (0.97, 95% CI: 0.80-0.99) niches. Both predators relied on seasonally abundant marmots (Marmota caudata) rather than wild ungulates, their typical primary prey, suggesting that despite patterns of overlap that were superficially conducive to exploitation competition and predator facilitation, prey were likely not a limiting factor. Therefore, prey-mediated interactions, if present, were unlikely to be a major structuring force in the ecosystem. By implication, carnivore conservation planning and monitoring in the mountains of Central Asia should more fully account for the seasonal importance of marmots in the ecosystem.
... All of these variables will affect the number of opportunities a virus has to jump from one host species to another, in turn shaping the diversity and abundance of viruses in populations. There has been considerable interest in understanding the interactions between predators and prey, and how this affects behavior, population trends, and geographical distributions [37]. Viral infection is likely to cause changes in host interactions and population dynamics, including mortality and reproductive rates (Figure 3), impacting key aspects of population ecology including predator-prey interactions and interspecific competition. ...
... There is considerable interest in understanding how communities interact [37,47]. Differences in abiotic conditions between communities impact viruses by affecting host behavior and distribution ( Figure 2). ...
Article
Understanding the emergence of pathogenic viruses has dominated studies of virus evolution. However, new metagenomic studies imply that relatively few of an immense number of viruses may lead to overt disease. This suggests a change in emphasis, from viruses as habitual pathogens to integral components of ecosystems. Here we show how viruses alter interactions between host individuals, populations, and ecosystems, impacting ecosystem health, resilience, and function, and how host ecology in turn impacts viral abundance and diversity. Moving to an ecosystems perspective will put virus evolution and disease emergence in its true context, and enhance our understanding of ecological processes.
... Concretely, we introduced predators to a simulated landscape and varied the size of their habitat domain as a measure of the area they threatened. Habitat domain is specifically the spatial extent over which individuals move while foraging, in contrast to home range which can encompass resources to meet other needs, and can also encompass what available microhabitat is used (Preisser et al., 2007;Schmitz et al., 2017). Foraging prey in these simulations differed in their knowledge of the surrounding landscape and how exploratory they were in the face of new habitat. ...
... Not surprisingly, therefore, predators with large domains induced prey to spend more time searching for refugia away from the introduction quadrant and, as a result, to suffer increased penalties to consumption. Interestingly, when also considering forager memory, our findings align broadly with the "hunting mode-habitat domain" concept (Schmitz et al., 2017;Wirsing et al., 2021). Under this framework, prey with domains that extend beyond those of their predators should rely on avoidance to minimize encounters, whereas those whose domains fall within that of a predator are expected to experience more encounters and utilize defenses that reduce the likelihood of death given an encounter. ...
Article
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Predator reintroductions are often used as a means of restoring the ecosystem services that these species can provide. The ecosystem consequences of predator reintroduction depend on how prey species respond. Yet, to date, we lack a general framework for predicting these responses. To address this knowledge gap, we modeled the impacts of predator reintroduction on foragers as a function of predator characteristics (habitat domain; i.e., area threatened) and prey characteristics (knowledge of alternative habitat and exploratory tendency). Foraging prey had the capacity to both remember and return to good habitat and to remember and avoid predators. In general, we found that forager search time increased and consumption decreased after predator introduction. However, predator habitat domain played a key role in determining how much prey habitat use changed following reintroduction, and the forager's knowledge of alternative habitats and exploratory inclinations affected what types of habitat shifts occurred. Namely, habitat shifts and consumption sacrifices by prey were extreme in some cases, particularly when they were pushed far from their starting locations by broad-domain predators, whereas informed foragers spent less time searching and displayed smaller reductions to consumption than their naïve counterparts following predator exposure. More exploratory foragers exhibited larger habitat shifts, thereby sacrificing consumption but reducing encounters by relocating to refugia, whereas less exploratory foragers managed risk in place and consequently suffered increased encounters while consuming more resources. By implication, reintroductions of predators with broad habitat domains are especially likely to impose foraging and movements costs on prey, but forager spatial memory state can mitigate these effects, as informed foragers can better access alternate habitat and avoid predators with smaller reductions in consumption.
... This is because the numeric response of higher elevation mountain lions is tied to higher elevation, higher quality mule deer density (Table 1, Figure 2). Thus, mountain lion predation rates on juvenile mule deer are predicted to remain constant as overall mule deer density increased because territoriality of deer means that such density increases occurred only in lower quality, coyote areas at low elevation (Northfield et al. 2017;Schmitz et al. 2017). ...
... We thus predict that in areas with a left-skewed distribution of habitat quality (i.e., very few sites of high quality), spatial density dependence should be the strongest and should decrease with increasing abundance of high-quality sites. These conclusions are supported by recent spatial food-web modeling that clearly demonstrates the critical role of space and differential spatial overlap between predators and prey in determining predictions of density-dependent predation (Northfield et al. 2017;Schmitz et al. 2017). Ultimately, when resource abundance or forage quality directly determines spatial variation in habitat quality, food resources should be indirectly the mechanism. ...
Article
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Density‐dependent competition for food reduces vital rates, with juvenile survival often the first to decline. A clear prediction of food‐based, density‐dependent competition for large herbivores is decreasing juvenile survival with increasing density. However, competition for enemy‐free space could also be a significant mechanism for density dependence in territorial species. How juvenile survival is predicted to change across density depends critically on the nature of predator–prey dynamics and spatial overlap among predator and prey, especially in multiple‐predator systems. Here, we used a management experiment that reduced densities of a generalist predator, coyotes, and specialist predator, mountain lions, over a 5‐year period to test for spatial density dependence mediated by predation on juvenile mule deer in Idaho, USA. We tested the spatial density‐dependence hypothesis by tracking the fate of 251 juvenile mule deer, estimating cause‐specific mortality, and testing responses to changes in deer density and predator abundance. Overall juvenile mortality did not increase with deer density, but generalist coyote‐caused mortality did, but not when coyote density was reduced experimentally. Mountain lion‐caused mortality did not change with deer density in the reference area in contradiction of the food‐based competition hypothesis, but declined in the treatment area, opposite to the pattern of coyotes. These observations clearly reject the food‐based density‐dependence hypothesis for juvenile mule deer. Instead, our results provide support for the spatial density‐dependence hypothesis that competition for enemy‐free space increases predation by generalist predators on juvenile large herbivores.
... Smaller prey may forage locally, whereas larger prey may roam widely depending on their forage requirements in relation to the distribution of plant (or other resource) quality and productivity (Haskell et al. 2002), creating contingency in prey movement and habitat domain size. Further contingencies could arise if prey has different habitat domain sizes as they adjust their movements to the predator they face (Fischhoff et al. 2007;Merrill et al. 2010;Miller et al. 2014), or if predator or prey domains differ with density (Schmitz et al. 2017a). ...
... By synthesising the work and concepts of Heithaus et al. (2009) and Schmitz et al. (2017a), we present a new framework that integrates prey, predator and landscape traits to anticipate the form and magnitude of anti-predator behaviour. This framework is broadly applicable, as evidenced by its ability to retrospectively explain differences in behavioural countermeasures that have been observed in the field across a range of taxa. ...
... Natural populations of prey species often experience stressful environmental conditions that are shaped by both multiple predators and abiotic conditions (Schmitz et al., 2017). These environmental stressors are often important ecological and evolutionary drivers of phenotypic variation, and can vary in their relative importance among populations across the landscape (Nussey et al., 2007). ...
... However, the trade-offs associated with trait expression in natural populations are often poorly understood (Schmitz et al., 2017). ...
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Trait expression of natural populations often jointly depends on prevailing abiotic environmental conditions and predation risk. Copepods, for example, can vary their expression of compounds that confer protection against ultraviolet radiation (UVR), such as astaxanthin and mycosporine-like amino acids (MAAs), in relation to predation risk. Despite ample evidence that copepods accumulate less astaxanthin in the presence of predators, little is known about how the community composition of planktivo-rous fish can affect the overall expression of photoprotective compounds. Here, we investigate how the (co-)occurrence of Arctic charr (Salvelinus alpinus) and threespine stickleback (Gasterosteus aculeatus) affects the photoprotective phenotype of the co-pepod Leptodiaptomus minutus in lake ecosystems in southern Greenland. We found that average astaxanthin and MAA contents were lowest in lakes with stickleback, but we found no evidence that these photoprotective compounds were affected by the presence of charr. Furthermore, variance in astaxanthin among individual copepods was greatest in the presence of stickleback and the astaxanthin content of copepods was negatively correlated with increasing stickleback density. Overall, we show that the presence and density of stickleback jointly affect the content of photoprotective compounds by copepods, illustrating how the community composition of predators in an ecosystem can determine the expression of prey traits that are also influenced by abiotic stressors.
... Smaller prey may forage locally, whereas larger prey may roam widely depending on their forage requirements in relation to the distribution of plant (or other resource) quality and productivity (Haskell et al. 2002), creating contingency in prey movement and habitat domain size. Further contingencies could arise if prey has different habitat domain sizes as they adjust their movements to the predator they face (Fischhoff et al. 2007;Merrill et al. 2010;Miller et al. 2014), or if predator or prey domains differ with density (Schmitz et al. 2017a). ...
... By synthesising the work and concepts of Heithaus et al. (2009) and Schmitz et al. (2017a), we present a new framework that integrates prey, predator and landscape traits to anticipate the form and magnitude of anti-predator behaviour. This framework is broadly applicable, as evidenced by its ability to retrospectively explain differences in behavioural countermeasures that have been observed in the field across a range of taxa. ...
Article
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Non-consumptive predator effects (NCEs) are now widely recognised for their capacity to shape ecosystem structure and function. Yet, forecasting the propagation of these predator-induced trait changes through particular communities remains a challenge. Accordingly, focusing on plasticity in prey anti-predator behaviours, we conceptualise the multi-stage process by which predators trigger direct and indirect NCEs, review and distil potential drivers of contingencies into three key categories (properties of the prey, predator and setting), and then provide a general framework for predicting both the nature and strength of direct NCEs. Our review underscores the myriad factors that can generate NCE contingencies while guiding how research might better anticipate and account for them. Moreover, our synthesis highlights the value of mapping both habitat domains and prey-specific patterns of evasion success ('evasion landscapes') as the basis for predicting how direct NCEs are likely to manifest in any particular community. Looking ahead, we highlight two key knowledge gaps that continue to impede a comprehensive understanding of non-consumptive predator-prey interactions and their ecosystem consequences; namely, insufficient empirical exploration of (1) context-dependent indirect NCEs and (2) the ways in which direct and indirect NCEs are shaped interactively by multiple drivers of context dependence.
... Hence, habitat heterogeneity cannot be omitted for example when interpreting differences in S. exigua vs. B. tabaci parasitoid loads or biological control efficacy ( Figure 1C) and thus needs to feature in an inclusive, functional traitbased approach. Similarly, environmental heterogeneity shapes BCAs' habitat domain (i.e., the spatial extent of habitat space used), defines its overlap with that of target host or prey items and can help us to anticipate the outcomes of predatorprey interactions (Schmitz et al., 2017). In addition, other confounding factors include release numbers, which determine demographic factors such as Allee effects or genetic bottlenecks (Grevstad, 1999), environmental heterogeneity (Barajas- Barbosa et al., 2020) and the on-site presence of a seasoned biological control practitioner ( MJW Cock, personal comm.). ...
... For BCAs with varying functional traits (e.g., as deployed against common targets), conditional incidence can be examined for islands of varying size, heterogeneity or energy (Wright, 1983;Holt, 2009). Aside from yielding static, species specific attributes or inferences on specific predator x prey couplets (Massol et al., 2017;Schmitz et al., 2017), doing so can generate insights into how multiple BCAs act within dynamic communities. In the meantime, fieldwork needs to be conducted in a systematic manner -using standardized protocols-across different island and/or mountain settings (e.g., Borges et al., 2018). ...
Article
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For centuries, islands and mountains have incited the interest of naturalists, evolutionary biologists and ecologists. Islands have been the cradle for biogeography and speciation theories, while mountain ranges have informed how population adaptation to thermal floors shapes the distribution of species globally. Islands of varying size and mountains' altitudinal ranges constitute unique "natural laboratories" where one can investigate the effects of species loss or global warming on ecosystem service delivery. Although invertebrate pollination or seed dispersal processes are steadily being examined, biological control research is lagging. While observations of a wider niche breadth among insect pollinators in small (i.e., species-poor) islands or at high (i.e., colder) altitudes likely also hold for biological control agents, such remains to be examined. In this Perspective piece, we draw on published datasets to show that island size alone does not explain biological control outcomes. Instead, one needs to account for species' functional traits, habitat heterogeneity, host community make-up, phenology, site history or even anthropogenic forces. Meanwhile, data from mountain ranges show how parasitism rates of Noctuid moths and Tephritid fruit flies exhibit species-and context-dependent shifts with altitude. Nevertheless, future empirical work in mountain settings could clarify the thermal niche space of individual natural enemy taxa and overall thermal resilience of biological control. We further discuss how global databases can be screened, while ecological theories can be tested, and simulation models defined based upon observational or manipulative assays in either system. Doing so can yield unprecedented insights into the fate of biological control in the Anthropocene and inform ways to reinforce this vital ecosystem service under global environmental change scenarios.
... For example, the brief addition of Mole Salamander (Ambystoma talpoideum) larvae for 30 days in experimental ponds changed the species composition of zooplankton communities relative to no-salamander controls (Rudolf and Van Allen, 2017). Thus, the effects of predators can span across both spatial and temporal scales (Schmitz et al., 2017). ...
Article
While organisms are typically considered permanent residents of a community, many transient organisms occupy a community for only brief periods. Despite the duration, the effects of a short visit by a top predator may remain long after departure. To test hypotheses on the impacts of a short-term visit by a top predator on pond communities, we used artificial ponds and constructed food web treatments that varied in trophic structure (Control Food Web = no predators present, Bluegill Food Web = only intermediate predators present, and Full Food Web = top and intermediate predators present). The constructed food webs were replicated five times and contained two prey species (frog tadpoles), an intermediate predator (fish), and one top predator (freshwater turtle). The Full Food Web simulated a four-day visit by Chelydra serpentina (Common Snapping Turtle). Predation by Lepomis macrochirus (Bluegill) reduced mean tadpole survival for Hyla chrysoscelis (Cope's Gray Tree Frog) in all food webs, including the Full Food Web with C. serpentina, compared to the Control Food Web. Although C. serpentina had no effects on tadpoles of H. chrysoscelis, the top predator reduced mean survival and increased mean mass of Rana sphenocephala (Southern Leopard Frog) when compared to the Bluegill Food Web. Therefore, our results suggest that brief visits from transient organisms, especially top predators, can alter community structure and initiate cascading effects.
... In plant communities, the ecological dynamics are shaped mostly by competition for light and nutrients 43 as well as by facilitation 44 . In communities of predators and prey, interactions are based on encounter rates and thus by the movements of individuals 45 . In all these cases, the interaction strength is expected to decline with distance between individuals. ...
Article
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Communities of interacting microorganisms play important roles across all habitats on Earth. These communities typically consist of a large number of species that perform different metabolic processes. The functions of microbial communities ultimately emerge from interactions between these different microorganisms. To understand the dynamics and functions of microbial communities, we thus need to know the nature and strength of these interactions. Here, we quantified the interaction strength between individual cells in microbial communities. We worked with synthetic communities of Escherichia coli bacteria that exchange metabolites to grow. We combined single-cell growth rate measurements with mathematical modelling to quantify metabolic interactions between individual cells and to map the spatial interaction network in these communities. We found that cells only interact with other cells in their immediate neighbourhood. This short interaction range limits the coupling between different species and reduces their ability to perform metabolic processes collectively. Our experiments and models demonstrate that the spatial scale of biotic interaction plays a fundamental role in shaping the ecological dynamics of communities and the functioning of ecosystems. By quantifying metabolic interactions between individual cells in synthetic microbial communities, the authors show that interactions are extremely localized, and that the spatial scale of interactions influences community dynamics.
... Puisque les ajustements d'utilisation de l'espace par les proies en réaction aux prédateurs peuvent fortement impacter la structure et le fonctionnement des écosystèmes (p. ex.,Suraci et al. 2016), il est important de bien identifier les mécanismes en cause si nous voulons prévoir comment les communautés écologiques vont changer dans le temps(Schmitz et al. 2017). Mon étude contribue à cet objectif en apportant du soutien au jeu de passe-passe comme mécanisme explicatif de l'utilisation de l'espace des prédateurs et des proies.Dans le chapitre 2, j'aborde essentiellement l'impact direct de la prédation sur l'abondance de la population de bisons du PNPA. ...
Thesis
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Determining the factors that shape patterns of animal distribution and abundance is a major topic in contemporary ecological research. The overarching objective of my thesis was to better understand how one such factor, predation – in its broader meaning to include harvesting by humans – influences the links between space use and population dynamics. My work explores the links between predation risk, movement and habitat selection, mortality rates and the viability of a threatened population of large herbivore. The study system was the plains bison (Bison bison bison) population of Prince Albert National Park, Saskatchewan, subject most notably to predation by grey wolves (Canis lupus) and harvest by humans. In chapter 1, I use movement and habitat selection analyses to reveal the strategies of space use deployed by bison in response to wolves and vice-versa. From mid-summer to the onset of winter, bison reduced the time spent in patches rich in food as the long-term risk of encountering wolves there increased. Bison also left these patches more quickly when wolves were relatively close by. In winter, however, bison were observed to only react by moving away from nearby wolves. The absence of a bison response to the long-term risk of encountering wolves in winter could be explained by energetic constraints, as food is less digestible and movement more costly due to snow cover during this season. Although I reveal that perceived predation risk influences bison use of space, I show in chapter 2 that neither wolf predation nor disease (in the form of anthrax outbreaks) represent a threat to the viability of the population. Rather, the main reason behind a probability of population extinction of 66% over the next 50 years under current conditions is the legal, yet unregulated, harvest by native hunters. Bison are vulnerable to harvest when they leave the park to forage on rich food available in agricultural fields. My analyses refine our understanding of this pattern by showing that every additional 1% of time spent in fields with hunting permission from 2011 to 2016 increased the risk of harvest mortality by 9%. I also reveal that the time bison spend in such fields must drop by 70% for population abundance to remain stable at its current level in a scenario of continued wolf predation and anthrax outbreaks. More than 70% of bison use of fields with hunting permission were limited to just five fields. Management interventions targeting these riskier fields would be an effective short-term strategy to halt the population’s decline. Even though such an approach might lead bison to increase their use of other fields, the demographic impact of harvesting should consequently diminish, at least over the short term, given that harvesting is not permitted in most other fields used by bison. Finally, in chapter 3, I use an individual-based model to compare the relative effectiveness of different management interventions manipulating food profitability (i.e. the ratio between digestible energy and handling time) and distribution to reduce the time bison spend outside the park raiding crops and, thereby, the number of individuals harvested. My simulations suggest that draining meadows inside the park to increase the availability of natural forage there would not be very effective. However, my simulations also suggest that cultivating crops outside the park of lower profitability relative to natural forage inside the park would be a better intervention. My thesis reveals the dynamic and complex nature of the anti-predator movement and habitat selection strategies deployed by a large herbivore in a multi-prey system. My work also highlights the practical interest of linking spatial distribution to population viability to lead to more effective management interventions. The overall result is a thorough case study aimed at improving our ability, over the short term, to conserve populations vulnerable to threats which are distributed heterogeneously in space.
... How individuals use space shapes ecological dynamics by affecting the strength of interactions between species (Lampert & Hastings, 2016;Schmitz, Miller, Trainor, & Abrahms, 2017). Predators and prey are in many cases expected to shape each other's spatial distributions. ...
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Predators and prey are often engaged in a game where their expected fitnesses are affected by their relative spatial distributions. Game models generally predict that when predators and prey move at similar temporal and spatial scales that predators should distribute themselves to match the distribution of the prey's resources and that prey should be relatively uniformly distributed. These predictions should better apply to sit‐and‐pursue and sit‐and‐wait predators, who must anticipate the spatial distributions of their prey, than active predators that search for their prey. We test this with an experiment observing the spatial distributions and estimating the causes of movements between patches for Pacific tree frog tadpoles (Pseudacris regilla), a sit‐and‐pursue dragonfly larvae predator (Rhionaeschna multicolor), and an active salamander larval predator (Ambystoma tigrinum mavortium) when a single species was in the arena and when the prey was with one of the predators. We find that the sit‐and‐pursue predator favors patches with more of the prey's algae resources when the prey is not in the experimental arena and that the prey, when in the arena with this predator, do not favor patches with more resources. We also find that the active predator does not favor patches with more algae and that prey, when with an active predator, continue to favor these higher resource patches. These results suggest that the hunting modes of predators impact their spatial distributions and the spatial distributions of their prey, which has potential to have cascading effects on lower trophic levels. Proportions (with SE bars) of tadpoles in the four resource patch types differing in amount of prey resource present for T, TD, and TS treatments. * indicates that the slope of number of tadpoles in a patch versus the resources in the patch significantly differed from 0.
... Our results are, however, not immediately applicable to passively moving species for which movement speed and body size are inversely related (De Bie et al., 2012). An important limitation to the study is that movement of herbivores is only influenced by the basal resource and not the predator, so non-lethal effects acting in landscapes of fear are not considered (Bleicher, 2017;Schmitz, Miller, Trainor & Abrahms, 2017). Moreover, movement decisions are assumed to be completely informed in our model, while we demonstrated earlier that the level of information strongly affects body size responses to habitat fragmentation (Hillaert, Vandegehuchte, et al., 2018b). ...
Article
In the absence of predators, habitat fragmentation favors large body sizes to facilitate gap‐crossing. The size of primary consumers is, however, also shaped by top‐down effects as predators select prey of a certain size. Therefore, higher trophic levels should be taken into consideration when studying the effect of habitat loss and fragmentation on size distributions of herbivores. We built a model to study the effect of habitat loss and fragmentation within a tri‐trophic food chain. Body size is directly linked to movement capacity and metabolic processes and considered as a master trait under selection. We show that basal resources accumulate locally if a predator causes top‐down control of the herbivore. Due to this increasing spatiotemporal variability in resource availability, larger herbivores are selected than in scenarios without predator as they are able to move further. As predators cause herbivores to be intrinsically much larger than the optimal sizes selected by habitat fragmentation in the absence of predators, habitat fragmentation is no longer a significant driver of herbivore size. However, there is selection for increased predator size with habitat fragmentation as herbivores become less abundant, hence favoring gap‐crossing ability of the predator. Since herbivore and predator body size respond differently to habitat loss and fragmentation, realized predator‐herbivore body size ratios increase along this fragmentation gradient. Our model demonstrates how feedbacks between the abundance, body size, and mobility of predators and prey ultimately determine body size distributions in food webs. These new insights shed light on the impact of habitat destruction and fragmentation on overall food web structure.
... Thus, like predation risk itself, prey responses to risk are expected to be temporally dynamic (Lima and Bednekoff 1999). Temporal shifts in prey behavior, for example, are common in systems where predator diel schedules are fixed (Schmitz et al. 2017). Second, the risk allocation hypothesis predicts that individuals in better nutritional condition can afford to be more risk averse, spending energetic reserves or incurring opportunity costs to avoid perceived threats. ...
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The life-and-death stakes of predator-prey encounters justify the high price of many anti-predator behaviors. In adopting these behaviors, prey incur substantial non-consumptive costs that can have population-level consequences. Because prey knowledge of risk is imperfect, individuals may even adopt these costly behaviors in the absence of a real threat. For example, rather than only avoid hunters, many species categorically avoid all anthropogenic activity. Although hunting seasons only increase risk for specific individuals (e.g., males), non-target individuals may still perceive human hunters as a source of risk and respond accordingly. Here, we used a large-scale experiment including 89 animal-years of location data from 62 unique individuals over 6 yr to quantify the duration, magnitude, and energetic consequences of changes to movement and resource selection behavior adopted by non-target female elk (Cervus canadensis) in response to human hunters during three separate experimental 5-d hunts (elk archery, deer rifle (Odocoileus hemionus or Odocoileus virginianus), and elk rifle). We predicted that elk response to hunters would be brief, but that strong behavioral responses to hunters (e.g., strengthened avoidance of roads and trails) would carry nutritional costs. We measured the duration of hunt-related changes in elk speed using quantile regression, further quantified the strength of elk behavioral responses to hunters using population-level resource selection functions, and evaluated whether anti-predator resource selection behavior translated to measurable metabolic costs in the form of reduced body fat heading into winter. Elk responses to human hunters were stronger in the day than at night and were generally more pronounced during the elk hunts than during deer hunts. During hunts, elk shifted their diurnal behavior to avoid forage and intensified their avoidance of roads and trails. The combination of these changes in behavior led to a predicted pattern of distribution during the hunt that differed substantially from the distribution prior to the hunt. Lactating females that more strongly avoided roads entered winter in poorer nutritional condition, suggesting that the changes in resource selection we describe carry corresponding nutritional costs that have the potential to impact subsequent population performance.
... Competition for shared prey resources between interspecific predators can weaken the link between prey availability and predation rate (Abrams & Ginzburg, 2000;Arditi & Ginzburg, 2012). Thus, there is an increasing interest in how competing predators respond to prey availability and if the predictions from theoretical models of predator-prey dynamics are realized in wildlife populations under natural conditions (Chan et al., 2017;Schmitz, Miller, Trainor, & Abrahms, 2017;Wasserman et al., 2016). ...
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The relationship between the rate of predation and prey abundance is an important component of predator‐prey dynamics. However, functional responses are less straightforward when multiple predators compete for shared prey. Interactions among competing predators can reduce or enhance effects of predation on prey populations. Because many avian populations experience high rates of nest predation, understanding the role of specific predators on nest mortality will lead to more informed conservation and management strategies which attempt to increase productivity by removing certain predators or managing habitat to limit their impact. Our goal was to evaluate effects of specific predators and the influence of nest abundance on nest mortality. We monitored snowy plover Charadrius nivosus nests across 7 years at two study areas in Utah, USA with remote cameras. We modeled predator‐specific hazard rates for nest mortality in a Bayesian framework to assess relationships between competing predators and the role of nest abundance on predator‐specific hazard rates. We found that hazard rates for nest mortality by gulls Larus spp. decreased with increasing nest abundance, whereas nest mortality by foxes Vulpes spp. and ravens Corvus corax initially increased, indicating that dietary switching may occur when nests become more abundant. Nest mortalities of specific predators were often not independent and ranged between compensatory (e.g., mammalian mesopredators), and superadditive (e.g., avian predators) across the breeding season The non‐independence between nest mortalities suggests that reductions in some predators may not translate to additive increases in overall nest success. Analyses of cause‐specific mortality are rarely applied to avian nests, but examination of interacting impacts among competing predators on nest survival may provide insight into specific drivers of avian population dynamics.
... Species interactions can have dramatic effects on the distribution of biogenic habitat and ecosystem processes at large spatial scales (Atwood et al. 2015, Schmitz et al. 2017, Tarnita et al. 2017). Our study attempted to link herbivore behavior at local scales with pattern formation in coral reef landscapes across 10s−100s of km 2 . ...
... In consumer-resource interactions, the first step in the interaction sequence is spatiotemporal overlap-when consumers and resources occupy the same area at the same time (Schmitz et al. 2017). Consumers should generally seek to increase this overlap, while their resources should attempt to reduce it (i.e., the space-race concept; Sih 2005); mobile prey have a great advantage in this compared to plants. ...
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The risk of consumption is a pervasive aspect of ecology and recent work has focused on synthesis of consumer–resource interactions (e.g., enemy–victim ecology). Despite this, theories pertaining to the timing and magnitude of defenses in animals and plants have largely developed independently. However, both animals and plants share the common dilemma of uncertainty of attack, can gather information from the environment to predict future attacks and alter their defensive investment accordingly. Here, we present a novel, unifying framework based on the way an organism’s ability to defend itself during an attack can shape their pre-attack investment in defense. This framework provides a useful perspective on the nature of information use and variation in defensive investment across the sequence of attack-related events, both within and among species. It predicts that organisms with greater proportional fitness loss if attacked will gather and respond to risk information earlier in the attack sequence, while those that have lower proportional fitness loss may wait until attack is underway. This framework offers a common platform to compare and discuss consumer effects and provides novel insights into the way risk information can propagate through populations, communities, and ecosystems.
... For example, encounter rates between predators and their native prey species would be reduced if they have mismatched movement responses; however, for matrix-preferring predators this could be offset by higher encounter rates with livestock as an alternative source of prey. While wild prey may actively switch habitat preference to avoid predators (Schmitz et al. 2017), livestock may be more bounded by their association with humans and have lost many antipredator behaviors (Mignon-Grasteau et al. 2005) . ...
Thesis
Anthropogenic habitat destruction is one of the major causes of biodiversity loss, driving species declines across the planet. The resultant human-modified landscapes are not detrimental for all species. Some species such as small to medium-sized habitat generalist carnivores (hereafter referred to as ‘mesocarnivores’) are able to thrive because of the exclusion of natural enemies and anthropogenic sources of food. With the benefits of human-modified landscapes come novel threats, such as increased exposure to hunting and introduced antagonists. Mesocarnivores may respond to these threats with changes in space and time use, with potential consequences for species interactions. In this dissertation, I examine how drivers of mesocarnivore space and time use align with physical characteristics of the human-modified landscape and associated factors, and what implications these results have for interactions between native species. I do this using empirical work across two temperate systems (Chapters II, III, and IV), and a simulation model (Chapter V).
... Moreover, there are certainly more dimensions that could be added to this concept, which could either be direct species-related effects (e.g., maneuverability (Wilson et al., 2018), diurnal versus. nocturnal activity (Emmons, 1987;Jaksić, 1982)), habitat domains, or indirect effects (e.g., habitat structure (Cresswell, Lind, & Quinn, 2010;Laundré, Hernández, & Ripple, 2010;Schmitz, Miller, Trainor, & Abrahms, 2017)). This is consistent with general analyses across ecosystems showing that trophic niches in complex food webs can be characterized by up to eight dimensions (Eklöf et al., 2013). ...
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• Realized trophic niches of predators are often characterized along a one‐dimensional range in predator–prey body mass ratios. This prey range is constrained by an “energy limit” and a “subdue limit” toward small and large prey, respectively. Besides these body mass ratios, maximum speed is an additional key component in most predator–prey interactions. • Here, we extend the concept of a one‐dimensional prey range to a two‐dimensional prey space by incorporating a hump‐shaped speed‐body mass relation. This new “speed limit” additionally constrains trophic niches of predators toward fast prey. • To test this concept of two‐dimensional prey spaces for different hunting strategies (pursuit, group, and ambush predation), we synthesized data on 63 terrestrial mammalian predator–prey interactions, their body masses, and maximum speeds. • We found that pursuit predators hunt smaller and slower prey, whereas group hunters focus on larger but mostly slower prey and ambushers are more flexible. Group hunters and ambushers have evolved different strategies to occupy a similar trophic niche that avoids competition with pursuit predators. Moreover, our concept suggests energetic optima of these hunting strategies along a body mass axis and thereby provides mechanistic explanations for why there are no small group hunters (referred to as “micro‐lions”) or mega‐carnivores (referred to as “mega‐cheetahs”). • Our results demonstrate that advancing the concept of prey ranges to prey spaces by adding the new dimension of speed will foster a new and mechanistic understanding of predator trophic niches and improve our predictions of predator–prey interactions, food web structure, and ecosystem functions.
... Our study demonstrates that the physiology and ability to detect jellyfish tissue by phyllosomas of the lobster T. australiensis may be impaired under ∆pH = against predators (Paracer and Ahmadjian, 2000;Masuda, 2009). Inter-species interactions may help support populations of a species and thus benefit biodiversity (Paracer and Ahmadjian, 2000;Schmitz et al., 2017). However, anthropogenic stressors can threaten these interactions Draper and Weissburg, 2019). ...
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Ocean acidification (OA) can alter the behaviour and physiology of marine fauna and impair their ability to interact with other species, including those in symbiotic and predatory relationships. Phyllosoma larvae of lobsters are symbionts to many invertebrates and often ride and feed on jellyfish, however OA may threaten interactions between phyllosomas and jellyfish. Here, we tested whether OA predicted for surface mid-shelf waters of Great Barrier Reef, Australia, under ∆ pH = −0.1 (pH ~7.9) and ∆pH = −0.3 (pH ~7.7) relative to the present pH (~8.0) (P) impaired the survival, moulting, respiration, and metabolite profiles of phyllosoma larvae of the slipper lobster Thenus australiensis, and the ability of phyllosomas to detect chemical cues of fresh jellyfish tissue. We discovered that OA was detrimental to survival of phyllosomas with only 20% survival under ∆pH = −0.3 compared to 49.2 and 45.3% in the P and ∆pH = −0.1 treatments, respectively. The numbers of phyllosomas that moulted in the P and ∆pH = −0.1 treatments were 40% and 34% higher, respectively, than those in the ∆pH = −0.3 treatment. Respiration rates varied between pH treatments, but were not consistent through time. Respiration rates in the ∆pH = −0.3 and ∆pH = −0.1 treatments were initially 40% and 22% higher, respectively, than in the P treatment on Day 2 and then rates varied to become 26% lower (∆pH = −0.3) and 17% (∆pH = −0.1) higher towards the end of the experiment. Larvae were attracted to jellyfish tissue in treatments P and ∆pH = −0.1 but avoided jellyfish at ∆pH = −0.3. Moreover, OA conditions under ∆pH = −0.1 and ∆pH = −0.3 levels reduced the relative abundances of 22 of the 34 metabolites detected in phyllosomas via Nuclear Magnetic Resonance (NMR) spectroscopy. Our study demonstrates that the physiology and ability to detect jellyfish tissue by phyllosomas of the lobster T. australiensis may be impaired under ∆pH = −0.3 relative to the present conditions, with potential negative consequences for adult populations of this commercially important species.
... They can decrease the foraging efficiency of prey and their food quality, alter grouping patterns and intraspecific interactions, and can increase stress levels (Preisser & Bolnick, 2008). These responses and their consequences are not necessarily the same in all prey species and environments, and they may vary according to the predator's hunting mode (Preisser et al., 2007), the prey's ability to perceive risk (Jordan & Ryan, 2015) and to the spatiotemporal distribution of predation risk (Creel et al., 2008), generating different short-and long-term scenarios in which antipredator responses can occur (Creel et al., 2008;Schmitz et al., 2017). ...
Article
Predators can generate physiological and behavioural responses in prey individuals. Thus, carnivore reintroductions might cause profound changes in communities and ecosystems by modifying antipredator responses. Combining observational and experimental approaches, we compared the short- and long-term antipredator responses of capybaras, Hydrochoerus hydrochaeris, between a landscape with a high density of predators (Pantanal, Brazil) and a landscape where predators became extinct in the mid-20th century but where a jaguar reintroduction project was in progress (Iberá, Argentina). Generalized linear models were used to test whether the presence of natural predators affects capybara behavioural budgets, gregarious behaviour and the associated physiological stress responses and to test whether, in the short term, capybaras increase their vigilance levels after detecting the proximity of a simulated predator (a playback of jaguar, Panthera onca, calls). Capybaras in the Pantanal did not show higher levels of vigilance but they spent a greater proportion of time foraging than did capybaras in Iberá. Pantanal groups were smaller and foraged closer to water. The baseline levels of stress hormones tended to be higher in Iberá. In response to simulated stimuli, both populations responded to predator sound cues by increasing vigilance, but Iberá groups also increased vigilance in response to a control sound, suggesting that they did not recognize the predator stimulus as a greater risk than another stimulus. In areas with predators, capybaras may reduce predation risk by choosing safer areas, where they can spend more time foraging when predators are not nearby. Vigilance may be only a reactive response to cues of the predator's proximity. Understanding the capybara's antipredator responses may help predict the potential effects and the success of jaguar reintroduction in a region where the jaguar has been absent for over 80 years.
... Heterogeneity in the structure and configuration of habitat can mediate predator-prey interactions through its influence on the density and type of functional response exhibited by predators [12,13]. Habitat is a determining factor in the hunting capacity of predators, and the ability of prey to detect, avoid, or escape predators [14,15]. Changes in habitat complexity through human modification could hypothetically alter the outcome of species interactions through altering the functional response, attack rate, and handling time of predators [16]. ...
Article
Ongoing recovery of native predators has the potential to alter species interactions , with community and ecosystem wide implications. We estimated the co-occurrence of three species of conservation and management interest from a multi-species citizen science camera trap survey. We demonstrate fundamental differences in novel and coevolved predator-prey interactions that are mediated by habitat. Specifically, we demonstrate that anthropogenic habitat modification had no influence on the expansion of the recovering native pine marten in Ireland, nor does it affect the predator's suppressive influence on an invasive prey species, the grey squirrel. By contrast, the direction of the interaction between the pine marten and a native prey species, the red squirrel , is dependent on habitat. Pine martens had a positive influence on red squirrel occurrence at a landscape scale, especially in native broadleaf woodlands. However, in areas dominated by non-native conifer plantations, the pine marten reduced red squirrel occurrence. These findings suggest that following the recovery of a native predator, the benefits of competitive release are spatially structured and habitat-specific. The potential for past and future landscape modification to alter established interactions between predators and prey has global implications in the context of the ongoing recovery of predator populations in human-modified landscapes.
... Given known predator effects on biogeochemical cycling (Hawlena et al. 2012, Strickland et al. 2013, Leroux and Schmitz 2015, Schmitz et al. 2017a, it seems clear that both predation and perceived predation risk can drive spatial patterns of nutrient transport and accumulation. Yet despite this logical link between predator effects and nutrient distributions (Abrams 2000, the varied roles of predators as drivers of landscape heterogeneity remain largely unexplored (Anderson et al. 2008). ...
Article
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Spatial heterogeneity in ecological systems can result from animal-driven top-down processes, but despite some theoretical attention, the emergence of spatial heterogene-ity from feedbacks caused by animals is not well understood empirically. Interactions between predators and prey influence animal movement and associated nutrient transport and release, generating spatial heterogeneity that cascades throughout ecological systems. Here, we synthesize the existing literature to evaluate the mechanisms by which terrestrial predators can generate spatial heterogeneity in biogeochemical processes through consumptive and non-consumptive effects. Overall, we propose that predators increase heterogeneity in ecosystems whenever predation is intense and spatially variable, whereas predator-prey interactions homogenize ecosystems whenever predation is weak or diffuse in space. This leads to several testable hypotheses: 1) that predation and carcass deposition at high-predation risk sites stimulate positive feed-backs between predation risk and nutrient availability; 2) that prey generate nutrient hotspots when they concentrate activity in safe habitats, but instead generate nutrient subsidies when they migrate daily between safe and risky habitats; 3) that herbivore body size mediates risk effects, such that megaherbivores are more likely to homog-enize ecosystems and predator loss in general will tend to homogenize ecosystems. Testing these hypotheses will advance our understanding of whether predators amplify landscape heterogeneity in ecological systems.
... In accordance with our findings, the sequence of events by males during reproductive attempts has previously been mentioned as being indistinguishable from predation attempts (Gerritsen and Strickler 1977;Brewer 1998). Predator-prey interactions in a spatially explicit context have been extensively studied (Miller et al. 2014;Fortin et al. 2015;Schmitz et al. 2017), whereas the spatial ecology of sexual conflict has received relatively little attention. An emergent framework within the predator-prey domain aimed at clarifying and refocusing the effort to understand the spatial effects of risk is the "Landscape of Fear" (LOF) (Laundré et al. 2001(Laundré et al. , 2010(Laundré et al. , 2014Brown and Kotler 2004;Gaynor et al. 2019). ...
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Males and females often have divergent evolutionary interests, generating sexual conflicts. This is particularly true in organisms that exhibit facultative sexuality, whereby females are capable of reproducing without fitness costs of mating. Here, we provide the first documented evidence with quantitative tracking showing that sex interacts with social context to determine space-use of females, in a pattern resembling predator avoidance. To achieve this, we labelled Daphnia magna with fluorescent nanoparticles and utilized a 3-D tracking platform to record pairs of individuals swimming. The recordings comprised either same-sex or opposite-sex pairings. We found that females swam faster, deeper, more horizontally, and more linearly when exposed to males than when exposed to females. Simultaneously, we found that male behavior did not differ depending on swimming partner and, importantly, we observed no sexual dimorphism in swimming behaviors when swimming with the same sex. Our results suggest that the presence of males in a population has the potential to influence the distribution of individuals, similarly to known threats, such as predation. This highlights that sexual conflict has clear spatial consequences and should be considered in such ecological frameworks, like the Landscape of Fear (LOF) concept. In a broader context, the connection of the evolutionary and social concept of sexual conflict and the ecological concept of LOF may improve our understanding of population dynamics and the spatial and temporal distribution of individuals in natural ecosystems. Significance statement Despite the wealth of studies that detail how predators affect their prey’s spatial behaviors, studies on the role of sex and social context on spatial behavior are rare. Addressing this dearth of information, we studied the swimming behaviors of an organism that can reproduce with or without sex, when exposed to an individual of either the same or opposite sex. We found no difference between the sexes in swimming behaviors; however, we revealed that females avoided males by swimming deeper in the water column, reminiscent of the response to predation. Our results highlight that social conflict between the sexes strongly affects the demographics of a population and may therefore have a substantial role in the spatial ecology of organisms in the wild.
... The costs and benefits of habitat complexity might also differ when considering short-term versus long-term risk. If a predator species and a prey species rely on the same habitat features, the prey species can either increase antipredator behaviours because long-term risk is predictable in certain habitat types (Schmitz, Miller, Trainor, & Abrahms, 2017), or the predator can increase encounter rates with prey in the shared habitat because predators are able to readily predict the locations of prey (Smith et al., 2019). Thus, areas of dense vegetation might serve as a strong proxy for long-term predation risk in systems with ambush predators and induce increased antipredator behaviours to reduce the risk of detection or capture. ...
Article
Animals can reduce predation risk by increasing antipredator behaviours in areas of high long-term risk (risky places hypothesis), escalating antipredator behaviours when exposed to immediate risks (risky times hypothesis), varying responses to short-term risk based on long-term risk (risky times and risky places hypothesis, or predation risk allocation hypothesis) or altering antipredator behaviours based on habitat characteristics (habitat complexity risk mediation hypothesis). Most research on responses to predation risk has come from studies on herbivore prey, whereas little research has focused on mesopredator behavioural responses to risk. We studied antipredator behaviours of mesopredator cheetahs, Acinonyx jubatus, exposed to top predator risk from lions, Panthera leo, and leopards, Panthera pardus, by using a playback experiment to manipulate short-term predation risk in areas of differing long-term risk. We did not find support for the risky places hypothesis; cheetah vigilance was not influenced by long-term risk. On the contrary, we found support for the risky times hypothesis; cheetahs were more vigilant and more likely to flee following lion and leopard playbacks. Additionally, we did not find support for the risky times and risky places hypothesis or the predation risk allocation hypothesis; cheetah antipredator behaviours following a predator playback were not associated with long-term predation risk. Finally, cheetahs had higher baseline vigilance in areas of open vegetation but were more likely to flee from lion sounds in areas of dense vegetation and from leopards in areas of open vegetation. We highlight the importance of understanding spatial and temporal factors that influence mesopredator risk perception and show that antipredator behaviours can differ among trophic levels.
... There is a growing body of literature on predator-prey interactions in patchy landscapes (see e.g. Schmitz et al., 2017), yet this literature has yet to be integrated with the literature linking food web ecology and island biogeography, or SARs more broadly. We need theory linking island biogeography to food web ecology that better accounts for movements of animals among patches or sites at a range of spatial and temporal scales. ...
Chapter
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The species–area relationship (SAR) describes a range of related phenomena that are fundamental to the study of biogeography, macroecology and community ecology. While the subject of ongoing debate for a century, surprisingly, no previous book has focused specifically on the SAR. This volume addresses this shortfall by providing a synthesis of the development of SAR typologies and theory, as well as empirical research and application to biodiversity conservation problems. It also includes a compilation of recent advances in SAR research, comprising novel SAR-related theories and findings from the leading authors in the field. The chapters feature specific knowledge relating to terrestrial, marine and freshwater realms, ensuring a comprehensive volume relevant to a wide range of fields, with a mix of review and novel material and with clear recommendations for further research and application.
... Predation structures natural ecosystems (Schmitz et al. 2017). At the scale of populations, the intensity of predation is often characterised by the average predator's consumption of prey in relation to prey density, or the functional response (Holling 1959). ...
Article
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Spatial overlap between predator and prey is a prerequisite for predation, but the degree of overlap is not necessarily proportional to prey consumption. This is because many of the behavioural processes that precede ingestion are non-linear and depend on local prey densities. In aquatic environments, predators and prey distribute not only across a surface, but also vertically in the water column, adding another dimension to the interaction. Integrating and simplifying behavioural processes across space and time can lead to systematic biases in our inference about interaction strength. To recognise situations when this may occur, we must first understand processes underlying variation in prey consumption by individuals. Here we analysed the diet of a major predator in the Barents Sea, the Atlantic cod Gadus morhua, aiming to understand drivers of variation in cod's feeding on its main prey capelin Mallotus villosus. Cod and capelin only partly share habitats, as cod mainly reside near the seafloor and capelin inhabit the free water masses. We used data on stomach contents from ~2000 cod individuals and their surrounding environment collected over 12 years, testing hypotheses on biological and physical drivers of variation in cod's consumption of capelin, using generalized additive models. Specifically, effects of capelin abundance, capelin depth distribution, bottom depth and cod abundance on capelin consumption were evaluated at a resolution scale of 2 km. We found no indication of food competition as cod abundance had no effect on capelin consumption. Capelin abundance had small effects on consumption , while capelin depth distribution was important. Cod fed more intensively on capelin when capelin came close to the seafloor, especially at shallow banks and bank edges. Spatial overlap as an indicator for interaction strength needs to be evaluated in three dimensions instead of the conventional two when species are partly separated in the water column.
... Further complexities arise depending, for example, on the spatial scale of heterogeneity in stressor distributions relative to the organism's movement capacity (Schmitz et al. 2017;Fey et al. 2019). Although numerous studies have examined behavioural avoidance of one stressor, there is a need for a better understanding of factors that explain when and why multiple stressors are negatively versus positively correlated, and for more studies examining how organisms respond behaviourally to conflicting (e.g., negatively correlated) stressors, particularly in the broader context of additional layers of trade-offs. ...
Preprint
While a large body of research has focused on the physiological effects of multiple environmental stressors, behavioral effects remain far less studied. However, behavioural plasticity can not only directly drive responses to stressors but can also mediate physiological responses. Here, we provide a conceptual framework incorporating four fundamental tradeoffs explicitly linking animal behaviour to life history-based pathways for energy allocation, shaping the impact of multiple stressors on fitness. We first address how small-scale behavioural changes can drive conflicts between the effects of multiple stressors and alternative physiological responses. We then discuss how animal behaviour gives rise to three additional understudied and interrelated trade-offs: balancing the benefits and risks of obtaining the energy needed to cope with stressors, allocation of energy between life-history traits and stressor responses, and larger-scale escape from stressors in space or time via dispersal or dormancy. Finally, we outline how these trade-offs interactively affect fitness and qualitative ecological outcomes resulting from multiple stressors. Our framework suggests that animal behavior could underlie the extensive context dependence in results from stressor research, highlighting promising avenues for future empirical and theoretical research.
... These results add to other studies that demonstrate the effects of two engineers together are not always possible to predict from individual effects when they impact the same habitat or resource (Boye & Fong, 2005;Passarelli et al., 2014). While we did not dissect the mechanisms that underlie higher mud crab survival in Irish moss-mussel shell clumps, prior studies have linked enhanced prey survival to greater habitat complexity (Hughes & Grabowski, 2006;Waser, Splinter & Van der Meer, 2015;Schmitz et al., 2017). A rise in complexity can reduce predator-prey encounters or increase predator handling time, resulting in a reduction in predator foraging efficiency (Lima & Dill, 1990). ...
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In marine sedimentary bottoms, mussels and macroalgae have long been recognized as important autogenic engineers that create habitat and modify abiotic conditions. The structural complexity added by bivalves and macroalgae may also mediate intraguild predation amongst marine decapod crustaceans. While spatial distributions of these ecosystem engineers frequently overlap, there is limited understanding of compounded effects when more than one engineer is present. Here we demonstrate that the coexistence of two ecosystem engineers may create habitat valuable for the survival of a small native species, the Atlantic mud crab ( Panopeus herbstii ), in the presence of the invasive green crab ( Carcinus maenas ). Using laboratory and field habitat mimics, we measured mud crab survival rates as a proxy for refuge quality. We compared the refuge provided by a unique association between shells of blue mussels ( Mytilus edulis ) and the giant strain of Irish moss ( Chondrus crispus ) to that provided by bare substrate, and by each engineer alone. These experiments revealed that the association of giant Irish moss with blue mussel shells positively and non-additively increased mud crab survival compared to the other less complex habitat mimics. In contrast, parallel experiments revealed that high habitat complexity was less important for young green crabs to survive predation from large conspecifics. These results suggest that the impact of ecosystem engineers on trophic dynamics should be considered in a broader, whole-community context encompassing multiple habitat-forming species present.
... Although these types of studies are relatively easy to manipulate and replicate, they may not provide strong inference across broader landscapes and contexts (Lawton 1999, Schmitz et al. 2017). Understanding how landscape characteristics can mediate spatiotemporal interactions among carnivores is timely and warranted as land-use changes are occurring at rapid paces (Winkler et al. 2021, Kuipers et al. 2021). ...
Thesis
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The Great Plains region has undergone extensive conversion of native prairies to agriculture production and energy development since European colonization. Temperate prairies, including remaining prairies within the Great Plains, are considered among Earth’s most imperiled ecosystems. Prairie patches now exist as components of a landscape mosaic proportionately dominated by cultivated agriculture. These contemporary human-modified landscapes may structure species’ distributions, influence community dynamics, and supplant established abiotic range-limiting processes. Understanding the direction and scale of these processes, and how they are affected by landscape composition and configuration, is necessary to enhance conservation efforts. Carnivore communities may be most affected by landscape changes due to negative interactions with humans and their inherent biological traits; however, information regarding landscape-scale effects on the existing suite of carnivores in the Great Plains is lacking. I examined how landscape composition and characteristics influenced site occupancy probabilities and turnover rates by swift foxes (Vulpes velox), the spatial and temporal interactions between swift foxes and coyotes (Canis latrans), and carnivore richness in agro-prairie ecosystems. Additionally, I strategically identified native prairie areas to focus conservation and management of remaining swift fox habitat. During 2018-2020, I used detection/non-detection data from camera traps at 381 randomly selected sites distributed throughout a landscape mosaic comprising the westernmost 31 counties (7.16 million ha) of Kansas, USA. I subsequently used presence/absence data from these sites across three years to infer species-specific responses to landscape change and carnivore community dynamics. To evaluate effects of landscape composition and configuration on site occupancy probabilities and turnover rates by swift fox, I used a distance-weighted scale of effect of landscape metrics within multi-season occupancy models. Swift foxes were more likely to occur at sites with moderate landcover diversity within 254.47 ha, greater proportion of shortgrass prairie (7.07 ha) and loamy soil types (0.79 ha), and lower proportions of Conservation Reserve Program (CRP) landcover (78.54 ha). Swift foxes were more likely to colonize sites with less diverse landcover, a greater proportion of loamy soil types, and lower proportions of CRP landcover. Swift foxes were insensitive to the proportion of row-crop agriculture surrounding sites (3.14 ha). To evaluate landscape composition effects on swift foxes and coyote (the apex predator in the region) spatiotemporal interactions, I used a Bayesian hierarchical multi-season occupancy model to evaluate spatial interactions, and a coefficient of overlap of temporal activity to assess factors affecting temporal interactions. Mean persistence of swift foxes differed across sites where coyotes were not detected (0.66; SE = 0.001) and where coyotes were detected (0.39; SE=0.001). The coefficient of overlap at sites surrounded by lower proportions of CRP (≥0.10) differed (95% CIs did not overlap) from coefficient of overlap of all other landscape effects. The spatial distribution of swift foxes was positively influenced (Species Interaction Factor [SIF] > 1) by coyote presence through space and time at low proportions of CRP (≤0.04). SIF decreased as proportion of CRP increased; however, Bayesian confidence intervals overlapped SIF = 1, suggesting that swift foxes were spatially distributed independent of coyotes through space and time at greater proportions of CRP (>0.04). I used a structural equation model to test hypotheses of multiple direct and indirect relationships between landscape composition and configuration and prey availability on carnivore richness. My hypothesized model (X2 = 23.92, df = 24, P = 0.47) explained 27% of the variance of carnivore richness. Agriculture, native prairie, landcover diversity, CRP, water availability, prey occurrence, and sampling effort all had direct positive effects on my measure of carnivore richness, while loamy tableland soil had only an indirect effect. To strategically identify native prairie areas for conservation of swift fox habitat, I created a predicted swift fox occupancy map based on my most-supported, stacked single-season occupancy model. I identified predicted occupancy rate (range = 0.01–0.46) where sensitivity equaled specificity (0.09) within a receiver operating characteristic curve, and reclassified the predicted occupancy map to include only predicted occupancy rates >0.09, and again for a more targeted approach with predicted occupancy rates >0.18. These two maps were intersected with a map of grassland proportions >0.60 to identify areas that were expected to have relatively high occupancy and survival rates by swift fox. Swift foxes were more likely to occur at sites with low levels of landscape diversity (β = -0.411 ± 0.140), greater proportions of native grassland (β = 0.375 ± 0.154) and loamy tableland soils (β = 0.944 ± 0.188), and lower proportions of CRP landcover (β = -1.081 ± 0.360). Identified native grassland conservation areas totaled 84,420.24 ha (mean patch size = 162.66 ha [SE = 29.67]). Conservation areas located on privately owned working lands included 82,703.86 ha, while conservation areas located within the boundaries of federal, state, and non-governmental organizations (NGO) parcels included 1,716.38 ha. My results provide a unique understanding of how landscape composition and configuration, intraguild competition, and prey availability drive carnivore community dynamics in agro-prairie ecosystems. Additionally, my research elucidated constraints to range expansions for an iconic prairie-obligate carnivore (swift fox) at the edge of their range, while also identifying areas for strategic conservation for their populations.
... Inference based on observations of ecosystems with low consumer density may thus be highly misleading when applied to ecosystems with a high density of consumers, and vice-versa. Furthermore, understanding the influence of variation in consumer and resource densities on habitat selection could play a key role in understanding consumer-resource dynamics, as it defines how per capita consumption rate will vary over space and time(Matthiopoulos et al., 2015;Schmitz et al., 2017). ...
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... An agent's perceptual range can vary greatly with its body size (Mech & Zollner 2002;McGill & Mittelbach 2006), its needs and goals (Powell & Mitchell 2012), the ecosystem's structure (Pawar et al. 2012), and the presence or absence of other agents (Laundré et al. 2010;Northfield et al. 2017;Schmitz et al. 2017). Combining these approaches with seminal theoretical insights (e.g., Lima & Zollner 1996) and recent methodological advances (O'Connor et al. 2019; Riotte-Lambert & Matthiopoulos 2020) enables an investigation of how individual differences in perceptual abilities may be transmitted to populations, communities, and eventually ecosystems, and how these exchanges of information influence meta-community and meta-ecosystem dynamics (Guzman et al. 2019). ...
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Fluxes of matter, energy, and information over space and time contribute to ecosystems’ functioning. The meta-ecosystem framework addresses the dynamics of ecosystems linked by these fluxes, however, to date, meta-ecosystem research focused solely on fluxes of energy and matter, neglecting information. This is problematic due to organisms’ varied responses to information, which influence local ecosystem dynamics and can alter spatial flows of energy and matter. Furthermore, information itself can move between ecosystems. Therefore, information should contribute to meta-ecosystem dynamics, such as stability and productivity. Specific subdisciplines of ecology currently consider different types of information (e.g., social and cultural information, natural and artificial light or sound, body condition, genotype, and phenotype). Yet neither the spatiotemporal distribution of information nor its perception are currently accounted for in general ecological theories. Here, we provide a roadmap to synthesize information and meta-ecosystem ecology. We begin by defining information in a meta-ecological context. We then review and identify challenges to be addressed in developing information meta-ecology. Finally, we present new hypotheses for how information could impact dynamics across scales of spatio-temporal and biological organization.
... Most previous research on the role of habitat complexity on survival has been conducted in experimental systems with aquatic or insect species 20,21 , whereas less research has focused on wild mesopredator populations. The effects of vegetation complexity on mesopredator in wild population might be particularly complicated because of tradeoffs between hunting and protection from apex predators in different habitat types 1 . A greater understanding of how habitat characteristics such as vegetation complexity can influence mesopredator survival, is critical. ...
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Functional trait approaches in ecology chiefly assume the mean trait value of a population adequately predicts the outcome of species interactions. Yet this assumption ignores substantial trait variation among individuals within a population, which can have a profound effect on community structure and function. We explored individual trait variation through the lens of animal personality to test whether among‐individual variation in prey behavior mediates trophic interactions. We quantified the structure of personalities within a population of generalist grasshoppers and examined, through a number of field and laboratory‐based experiments, how personality types could impact tri‐trophic interactions in a food chain. Unlike other studies of this nature, we used spatial habitat domains to evaluate how personality types mechanistically map to behaviors relevant in predator–prey dynamics and found shy and bold individuals differed in both their habitat use and foraging strategy under predation risk by a sit‐and‐wait spider predator. In the field‐based mesocosm portion of our study, we found experimental populations of personality types differed in their trophic impact, demonstrating that prey personality can mediate trophic cascades. We found no differences in respiration rates or body size between personality types used in the mesocosm experiment, indicating relative differences in trophic impact were not due to variation in prey physiology but rather variation in behavioral strategies. Our work demonstrates how embracing the complexity of individual trait variation can offer mechanistically richer understanding of the processes underlying trophic interactions.
Chapter
Animal behaviors are governed by the intrinsic need to survive and reproduce. Even when sophisticated predators and prey are involved, these tenets of behavioral ecology hold. Similar to humans, fear can be a strong motivator for change in animals. The terrestrial ecology literature is replete with examples of fear-mediated behavioral effects on species and community networks. In contrast, the marine mammal literature is sparse in its recognition and consideration of nonconsumptive effects or risk effects arising from powerful and lethal predators, such as killer whales and large sharks. This chapter encapsulates the ecology of fear concept by providing representative examples from the marine mammal literature with consideration of prey and predator perspectives. Additionally, research data gaps and new avenues for scientific examination are highlighted within documented examples. Lastly, conservation practitioners and marine mammal scientists are encouraged to adapt theoretical concepts and methods from predation risk studies to better understand the effects of nonbiological stressors on marine mammal species.
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This book provides a first synthetic view of an emerging area of ecology and biogeography, linking individual- and population-level processes to geographic distributions and biodiversity patterns. Problems in evolutionary ecology, macroecology, and biogeography are illuminated by this integrative view. The book focuses on correlative approaches known as ecological niche modeling, species distribution modeling, or habitat suitability modeling, which use associations between known occurrences of species and environmental variables to identify environmental conditions under which populations can be maintained. The spatial distribution of environments suitable for the species can then be estimated: a potential distribution for the species. This approach has broad applicability to ecology, evolution, biogeography, and conservation biology, as well as to understanding the geographic potential of invasive species and infectious diseases, and the biological implications of climate change. The book lays out conceptual foundations and general principles for understanding and interpreting species distributions with respect to geography and environment. Focus is on development of niche models. While serving as a guide for students and researchers, the book also provides a theoretical framework to support future progress in the field.
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Foraging mode is a functional trait with cascading impacts on ecological communities. The foraging syndrome hypothesis posits a suite of concurrent traits that vary with foraging mode; however, comparative studies testing this hypothesis are typically interspecific. While foraging modes are often considered typological for a species when predicting foraging-related traits or mode-specific cascading impacts, intraspecific mode switching has been documented in some lizards. Mode-switching lizards provide an opportunity to test foraging syndromes and explore how intraspecific variability in foraging mode might affect local ecological communities.Because lizard natural history is intimately tied to habitat use and structure, I tested for mode switching between populations of the Aegean wall lizard, Podarcis erhardii, inhabiting undisturbed habitat and human-built rock walls on the Greek island of Naxos. I observed foraging behavior among 10 populations and tested lizard morphological and performance predictions at each site. Furthermore, I investigated the diet of lizards at each site relative to the available invertebrate community.I found that lizards living on rock walls were significantly more sedentary?sit and wait?than lizards at nonwall sites. I also found that head width increased in females and the ratio of hindlimbs to forelimbs in both sexes increased as predicted. Diet also changed, with nonwall lizards consuming a higher proportion of sedentary prey. Lizard bite force also varied significantly between sites; however, the pattern observed was opposite to that predicted, suggesting that bite force in these lizards may more closely relate to intraspecific competition than to diet.This study demonstrates microgeographic variability in lizard foraging mode as a result of human land use. In addition, these results demonstrate that foraging mode syndromes can shift intraspecifically with potential cascading effects on local ecological communities.
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Increased availability of high-resolution movement data has led to the development of numerous methods for studying changes in animal movement behavior. Path segmentation methods provide basics for detecting movement changes and the behavioral mechanisms driving them. However, available path segmentation methods differ vastly with respect to underlying statistical assumptions and output produced. Consequently, it is currently difficult for researchers new to path segmentation to gain an overview of the different methods, and choose one that is appropriate for their data and research questions. Here, we provide an overview of different methods for segmenting movement paths according to potential changes in underlying behavior. To structure our overview, we outline three broad types of research questions that are commonly addressed through path segmentation: 1) the quantitative description of movement patterns, 2) the detection of significant change-points, and 3) the identification of underlying processes or ‘hidden states’. We discuss advantages and limitations of different approaches for addressing these research questions using path-level movement data, and present general guidelines for choosing methods based on data characteristics and questions. Our overview illustrates the large diversity of available path segmentation approaches, highlights the need for studies that compare the utility of different methods, and identifies opportunities for future developments in path-level data analysis. Electronic supplementary material The online version of this article (doi:10.1186/s40462-016-0086-5) contains supplementary material, which is available to authorized users.
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Animals often breed in colonies that can vary in size by several orders of magnitude. Colony-size variation is perplexing because individuals in some colony sizes have lower fitness than those in other colony sizes, yet extensive size variation persists in most populations. Natural variation in colony size has allowed us to better quantify the costs and benefits of coloniality, but what causes and maintains size variation is in general unknown. Ecological correlates of colony-size variation potentially include local availability of resources, such as food or nesting sites, and may also reflect individuals’ sorting among colonies (based on life-history traits, morphology, or behavioral propensities) to find the social environment to which they are best suited. Preferences for particular colony sizes are genetically based in some species. The fitness differences observed among colony sizes may reflect unmeasured tradeoffs among life-history components and also could vary temporally or spatially. Colony-size variation might be maintained by fluctuating directional or stabilizing selection that alternately favors individuals in different group sizes and leads to stasis in the colony-size distribution over the long term. Recent focus on the cues individuals use to select breeding habitat (e.g., conspecific attraction, reproductive success of others) does not satisfactorily explain variation in colony size. Costs of dispersal, reliance on imperfect information, and collective nonrandom movement can also lead to colony-size variation in the absence of fitness-based site selection. Our understanding of factors generating and maintaining variation in colony size remains in its infancy and offers many opportunities for future research with broad implications for behavioral ecology.
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Hunting by humans constitutes a major source of mortality that selects for avoidance strategies. Group formation in eiders Somateria mollissima in response to hunting from motorboats was studied in the Danish Wadden Sea as an avoidance strategy to humans. In autumn the birds' food demand and energy consumption are relatively low and the need for optimal feeding opportunities are not as essential as during winter. We tested the hypothesis that eiders aggregate in groups of variable size dependent on predation risk (hunting), season and site. During autumn at the preferred feeding sites eiders occur in small numbers and group size increase together with hunting activity. Opposite during winter, eiders occur in large numbers and group size decrease when hunting activity increase. Hunting activity displaced eiders to adjacent sites with no or low hunting intensity and low food availability where group size of eiders increase during both autumn and winter in relation to the overall hunting activity. The formation into larger groups when hunting activity increase is probably due to increasing effects of vigilance and dilution, whereas formation into smaller groups is assumed to reduce the eiders conspicuousness to hunters. This change in group size made it possible for eiders to forage in areas with high food availability and high hunting intensity, while minimizing the risk of being detected by hunters. When the largest numbers of hunters were present at the preferred feeding site, group sizes during both autumn and winter were 110-125 eiders, indicating an optimal group size in relation to hunting density. Eiders located outside preferred feeding sites were in poorer body condition, suggesting that displacement was a suboptimal decision caused by hunting. We conclude that eiders adopted regrouping and displacement as two different strategies during hunting. Both strategies are tradeoffs between the risks of being detected by hunters and killed, and the benefits of feeding on mussel stocks thereby increasing body condition and hence fitness.
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There is a growing interest in using trait-based approaches to characterize the functional structure of animal communities. Quantitative methods have been derived mostly for plant ecology, but it is now common to characterize the functional composition of various systems such as soils, coral reefs, pelagic food webs or terrestrial vertebrate communities. With the ever-increasing availability of distribution and trait data, a quantitative method to represent the different roles of animals in a community promise to find generalities that will facilitate cross-system comparisons. There is, however, currently no theory relating the functional composition of food webs to their dynamics and properties. The intuitive interpretation that more functional diversity leads to higher resource exploitation and better ecosystem functioning was brought from plant ecology and does not apply readily to food webs. Here we appraise whether there are interpretable metrics to describe the functional composition of food webs that could foster a better understanding of their structure and functioning. We first distinguish the various roles that traits have on food web topology, resource extraction (bottom-up effects), trophic regulation (top-down effects), and the ability to keep energy and materials within the community. We then discuss positive effects of functional trait diversity on food webs, such as niche construction and bottom-up effects. We follow with a discussion on the negative effects of functional diversity, such as enhanced competition (both exploitation and apparent) and top-down control. Our review reveals that most of our current understanding of the impact of functional trait diversity on food web properties and functioning comes from an over-simplistic representation of network structure with well-defined levels. We, therefore, conclude with propositions for new research avenues for both theoreticians and empiricists.
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Context Many arboreal mammals in Neotropical forests are important seed dispersers that influence the spatial patterns of tree regeneration via their movement patterns, which in turn are determined by the canopy structure of the forest itself. However, the relationship between arboreal mammal movement and canopy structure is poorly understood, due in large part to the complexity of quantifying arboreal habitat structure. Objectives We relate detailed movement trajectories of three sympatric primate species to attributes of canopy structure derived from airborne light detection and ranging (LiDAR) in order to understand the role of structure in arboreal movement in the tropical moist forest of Barro Colorado Island, Panama. Methods We used high-resolution LiDAR to quantify three-dimensional attributes of the forest canopy of the entire island, high-resolution GPS tracking to map the movement patterns of the monkey species, and step selection functions to relate movement decisions to canopy attributes. Results We found that movement decisions were correlated with canopy height and distance to gaps, which indicate forest maturity and lateral connectivity, in all three species. In the two faster-moving species, step selection was also correlated with the thickness of the crown layer and the density of vegetation within the crown. Conclusions The correlations detected are fully in line with known differences in the locomotor adaptations and movement strategies of the study species, and directly reflect maximization of energetic efficiency and ability to escape from predators. Quantification of step selection in relation to structure thus provides insight into the ways in which arboreal animals use their environment.
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Interactions between large carnivores and other species may be responsible for impacts that are disproportionately large relative to their density. Context-dependent interactions between species are common but often poorly described. Caution must be expressed in seeing apex predators as ecological saviours because ecosystem services may not universally apply, particularly if inhibited by anthropogenic activity. This review examines how the impacts of large carnivores are affected by four major contexts (species assemblage, environmental productivity, landscape, predation risk) and the potential for human interference to affect these contexts. Humans are the most dominant landscape and resource user on the planet and our management intervention affects species composition, resource availability, demography, behaviour and interspecific trophic dynamics. Humans can impact large carnivores in much the same way these apex predators impact mesopredators and prey species - through density-mediated (consumptive) and trait/behaviourally-mediated (non-consumptive) pathways. Mesopredator and large herbivore suppression or release, intraguild competition and predation pressure may all be affected by human context. The aim of restoring ‘natural’ systems is somewhat problematic and not always pragmatic. Interspecific interactions are influenced by context, and humans are often the dominant driver in forming context. If management and conservation goals are to be achieved then it is pivotal to understand how humans influence trophic interactions and how trophic interactions are affected by context. Trade-offs and management interventions can only be implemented successfully if the intricacies of food webs are properly understood.
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A crucial element in the “the landscape of fear” concept is that prey animals are aware of varying levels of predation risk at a spatial scale. This often leads to a negative spatial relationship between prey and predator in which prey avoid the most risky sites in the landscape. In this paper we argue that our understanding of large carnivore-ungulate interactions is biased by studies from highly heterogeneous landscapes (e.g. the Yellowstone National Park). Due to a high availability of refuges and foraging sites in such landscapes, prey are able to reduce predation risk by showing habitat shifts. Besides the spatial heterogeneity at the landscape scale, the ungulate response to predation risk can be affected by the hunting mode (stalking vs. cursorial) of the predator. We propose that prey cannot easily avoid predation risk by moving to less risky habitats in more homogenous landscapes with concentrated food resources, especially where the large carnivores’ assemblage include both stalking and cursorial species. No distinct refuges for prey may occur in such landscapes due to equally high accessibility to predators in all habitats, while concentrated resources make prey distribution more predictable. We discuss a model of a densely-forested landscape based on a case study of the Białowieża Primeval Forest, Poland. Within this landscape ungulates focus their foraging activity on small food-rich forest gaps, which turn out to be “death traps” as the gaps are primarily targeted by predators (stalking lynx and cursorial wolf) while hunting. No alternative of moving to low predation risk areas exist for prey due to risk from wolves in surrounding closed-canopy forest. As a result the prey is exposed to constant high predation pressure in contrast to heterogeneous landscapes with less concentrated resources and more refuge areas. Future research should focus on explaining how ungulates are coping with predation risk in these landscapes that offer little choice of escaping predation by considering behavioral and physiological (e.g. metabolic, hormonal) responses.
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The indirect effects of predators on nonadjacent trophic levels, mediated through traits of intervening species, are collectively known as trait-mediated trophic cascades. Although birds are important predators in terrestrial ecosystems, clear examples of trait-mediated indirect effects involving bird predators have almost never been documented. Such indirect effects are important for structuring ecological communities and are likely to be negatively impacted by habitat fragmentation, climate change, and other factors that reduce abundance of top predators. We demonstrate that hummingbirds in Arizona realize increased breeding success when nesting in association with hawks. An enemy-free nesting space is created when jays, an important source of mortality for hummingbird nests, alter their foraging behavior in the presence of their hawk predators.
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Migratory ungulates outnumber residents by an order of magnitude in several savanna ecosystems in Africa, as was apparently the case in other grasslands around the world before the intervention of modern man. Migrants may be more numerous because 1) they use a much larger area, 2) they make more-efficient use of resources, or 3) they are less vulnerable to regulation by predators. These hypotheses were examined using simulation models of migratory and sedentary wildebeest Connochaetes taurinus in the Serengeti ecosystem. Simulations suggest that realistic numbers of predators could regulate resident herbivores at low population densities, whereas such regulation is probably rare for migratory herds. When residents and migrants have overlapping ranges, migrants should always outcompete residents, reducing them to low numbers. Results suggest that differences in the modes of regulation explain the predominance of migratory herbivores in some grassland ecosystems. -from Authors
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Movement data provide a window - often our only window - into the cognitive, social and biological processes that underlie the behavioural ecology of animals in the wild. Robust methods for identifying and interpreting distinct modes of movement behaviour are of great importance, but complicated by the fact that movement data are complex, multivariate and dependent. Many different approaches to exploratory analysis of movement have been developed to answer similar questions, and practitioners are often at a loss for how to choose an appropriate tool for a specific question. We apply and compare four methodological approaches: first passage time (FPT), Bayesian partitioning of Markov models (BPMM), behavioural change point analysis (BCPA) and a fitted multistate random walk (MRW) to three simulated tracks and two animal trajectories - a sea lamprey (Petromyzon marinus) tracked for 12 h and a wolf (Canis lupus) tracked for 1 year. The simulations - in which, respectively, velocity, tortuosity and spatial bias change - highlight the sensitivity of all methods to model misspecification. Methods that do not account for autocorrelation in the movement variables lead to spurious change points, while methods that do not account for spatial bias completely miss changes in orientation. When applied to the animal data, the methods broadly agree on the structure of the movement behaviours. Important discrepancies, however, reflect differences in the assumptions and nature of the outputs. Important trade-offs are between the strength of the a priori assumptions (low in BCPA, high in MRW), complexity of output (high in the BCPA, low in the BPMM and MRW) and explanatory potential (highest in the MRW). The animal track analysis suggests some general principles for the exploratory analysis of movement data, including ways to exploit the strengths of the various methods. We argue for close and detailed exploratory analysis of movement before fitting complex movement models.
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Identifying factors that may be responsible for regulating the size of animal populations is a cornerstone in understanding population ecology. The main factors that are thought to influence population size are either resources (bottom-up), or predation (top-down), or interspecific competition (parallel). However, there are highly variable and often contradictory results regarding their relative strengths and influence. These varied results are often interpreted as indicating "shifting control" among the three main factors, or a complex, nonlinear relationship among environmental variables, resource availability, predation, and competition. We argue here that there is a "missing link" in our understanding of predator-prey dynamics. We explore whether the landscape-of-fear model can help us clarify the inconsistencies and increase our understanding of the roles, extent, and possible interactions of top-down, bottom-up, and parallel factors on prey population abundance. We propose two main predictions derived from the landscape-of-fear model: (1) for a single species, we suggest that as the makeup of the landscape of fear changes from relatively safe to relatively risky, bottom-up impacts switch from strong to weak as top-down impacts go from weak to strong; (2) for two or more species, interspecific competitive interactions produce various combinations of bottom-up, top-down, and parallel impacts depending on the dominant competing species and whether the landscapes of fear are shared or distinctive among competing species. We contend that these predictions could successfully explain many of the complex and contradictory results of current research. We test some of these predictions based on long-term data for small mammals from the Chihuahuan Desert in the United States, and Mexico. We conclude that the landscape-of-fear model does provide reasonable explanations for many of the reported studies and should be tested further to better understand the effects of bottom-up, top-down, and parallel factors on population dynamics.