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Our understanding of ecosystem functioning is strongly linked to the study of predator–prey relationships and food web structures. However, trophic ecology has often focused on identifying taxonomic relationships and quantifying the biomass or energy ingested by consumers, but has often failed to integrate the importance of the nutritional quality of resources in ecological dynamics. Underlying this gap is the multi‐dimensional nature of resource quality which has hampered any consensus on the definition of resource nutritional quality. In this special issue, we aimed at gathering a subset of articles exemplifying the diversity of variables by which resources quality is quantified, the diversity of research topics that can be tackled in ecology – from physiological or evolutionary aspects to ecosystem processes – and propose some perspectives on the integration of nutritional quality within broader ecological concepts. Using a semi‐automated literature analysis, we map the current landscape of the 'resources nutritional quality' research of the last 30 years. We depict how it has been quantified through physical, biological or chemical indicators, the use of these parameters being largely dependent on the type of ecosystem studied and on the investigated ecological process. We then position the articles published in this special issue of Oikos within this landscape, showing they cover a small but relatively well representative subset of the domains of resources quality‐related issues. Articles in this special issue browse a range of individual and population‐level approaches (embracing evolutionary questions) to community related questions, include methodological issues and ecosystem‐wide approaches using trophic quality indicators as tracers of resources origin. Based on these studies and on the literature review, we identify a non‐exhaustive list of challenges and perspectives of research that we consider of highest priority in the large topic of trophic ecology. [ABSTRACT FROM AUTHOR]

Nestmate recognition is a widespread phenomenon and evolutionary important trait in the social insects. Yet evidence accumulates that the responses to non‐nestmates varies more than previously thought. We present a simple frequency‐dependent cost‐benefit model of nestmate recognition to understand conditions that might or might not favor the evolution of nestmate recognition that is based on cuticular hydrocarbon (CHC) profiles. Costs accounted for are costs for 1) maintaining a functional recognition system and 2) keeping a CHC profile that may be sub‐optimal regarding other functionalities like desiccation control, whereas the benefit of recognition is the prevention of nest raiding by other colonies. Unsurprisingly, the model indicates that recognition systems only evolve if costs are sufficiently low and benefits sufficiently high. In addition, the model suggests that nestmate recognition is more likely to evolve if colony turnover is fast (colony life‐expectancy is low). Our model creates evolutionary cycles that are typically longest under parameter combinations that just allow the evolution of recognition systems at all; the system expresses attributes of a rock‐paper‐scissors game. The model shows that a breakdown of nestmate recognition may occur under changing ecological situations, e.g. as a result of reduced intraspecific competition or increased abiotic stress. We speculate that such effects may be involved in the formation of supercolonies during invasions. Nestmate recognition may have evolved more to prevent interspecific predation or parasitism by antagonists that managed to mimic their host's CHC profile than as a mechanism to prevent exploitation by conspecific colonies. [ABSTRACT FROM AUTHOR]

Generalist predators whose primary prey undergoes cyclic fluctuations, will predate on alternate food sources when the abundance of their primary prey is low. In this paper we have developed a general model of a predator that switches predation between its primary prey and two alternative, competing, prey species. When the predators primary prey is at high abundance, predation of the alternate, competing, prey species is low, which provides periods of temporal refuge for the alternate prey from predation. When the inter‐specific interactions between the competing prey species lead to different dynamical outcomes in the presence and absence of predation, increasing the duration of the temporal refuge promotes dominance of a competitively superior species that is vulnerable to predation. The general theoretical framework was extended to consider a key case study system of pine marten predation on red and grey squirrels. In the absence of predation, grey squirrels out‐compete red squirrels but preferential predation by pine marten on grey squirrels can suppress grey squirrel density and allow red squirrel recovery. A temporal refuge for both squirrel species can arise due to prey switching by pine marten in years when field voles, their primary prey in the UK, are abundant. The duration of the temporal refuge, quantified as the relative length of the multi‐annual vole population cycle where vole density is above a population threshold, is a critical factor determining the persistence of red and grey squirrels. Our findings therefore provide insights for the conservation of the endangered red squirrel in the UK and the Republic of Ireland and more generally on the influence of the population dynamics of primary prey species in determining community composition. [ABSTRACT FROM AUTHOR]

Non-consumptive effects (NCEs) - changes in prey behavior or physiology in response to predator threat - are common and can be as strong as consumptive effects. However, our knowledge of NCEs in arthropod systems is lacking. Factors related to study organism and environment have the potential to influence the occurrence and magnitude of NCEs in arthropod systems. While factors such as coevolutionary history of natural enemies and their prey, predator cue, predator or prey feeding mode, and refuge availability have been theoretically and empirically examined, no trends have been proposed for arthropods. We compiled 62 studies, yielding 128 predator-prey interactions, which explicitly examined NCEs in experiments where arthropods were identified to species, using a previously published database of papers from 1990 to 2005 and a new database of papers published from 2006 to 2015. Using these data, we conducted a meta-analysis to explore the influence of organismal and environmental characteristics on the magnitude of predator NCEs. Our analysis addressed the following three questions. 1) Does predator-prey coevolution give rise to stronger NCEs than when predator and prey species did not coevolve? 2) What influence does habitat type and refuge availability have on NCEs? 3) How do predator characteristics (cue type, hunting mode and life stage) and prey characteristics (mobility, life stage, specialization, gregariousness and feeding mode) influence NCEs? We found that while NCEs were similar across most measured characteristics, NCEs on prey activity were significantly stronger when predator and prey shared an evolutionary history. Our results support growing evidence that NCEs have a negative effect on prey traits and that behavioral NCEs are stronger than physiological ones. Additional studies are needed to be confident in any emerging patterns, therefore we identify key gaps in the literature on NCEs in arthropod systems and discuss ideas for moving forward. [ABSTRACT FROM AUTHOR]

When navigating their lives through environments in which risks and rewards vary considerably in time and space, all biological organisms are continuously faced with uncertainty. The authors show that even though being distantly-related, prey species with shared predators may exchange information about the risk via mutually-recognized alarm signals, which in turn may lead to the emergence of taxonomically diverse information networks. [Extracted from the article]

Body size or mass is one of the main factors underlying food webs structure. A large number of evolutionary models have shown that indeed, the adaptive evolution of body size (or mass) can give rise to hierarchically organised trophic levels with complex between and within trophic interactions. However, these models generally make strong arbitrary assumptions on how traits evolve, casting doubts on their robustness. In particular, biomass conversion efficiency is always considered independent of the predator and prey size, which contradicts with the literature. In this paper, we propose a general model encompassing most previous models which allows to show that relaxing arbitrary assumptions gives rise to unrealistic food webs. We then show that considering biomass conversion efficiency dependent on species size is certainly key for food webs adaptive evolution because realistic food webs can evolve, making obsolete the need of arbitrary constraints on traits' evolution. We finally conclude that, on the one hand, ecologists should pay attention to how biomass flows into food webs in models. On the other hand, we question more generally the robustness of evolutionary models for the study of food webs. [ABSTRACT FROM AUTHOR]

Obligately cooperative breeders (cooperators) display a negative growth rate once they fall below a minimum density. Constraints imposed by natural enemies, such as predators or competitors, may push cooperator groups closer to this threshold, thus increasing the risk that stochastic fluctuations will drive them below it. This may indirectly drive these groups to extinction, thereby increasing the risk of population extinction. In this paper, we construct mathematical models of the dynamics of groups of cooperators and non-cooperators in the presence of two types of enemies: enemies whose dynamics do not depend on the dynamics of their victim (e.g., amensal competitor, generalist predator) and those whose dynamics do. In the latter case, we distinguish positive (e.g., specialist predator) and negative (e.g., bilateral competitor) reciprocal effects. These models correspond to the classical amensal, predation and competition models, in the presence of an Allee effect. We then develop the models to study consequences at the population level. By comparing models with or without an Allee effect, we show that enemies decrease the group size of cooperators more than that of non-cooperators, and this increases their group extinction risk. We also demonstrate how an Allee effect at a lower dynamical level can have consequences at a higher level: inverse density dependence at the group level generated lower population sizes and higher risks of population extinction. Our results also suggest that demographic compensation can be achieved by cooperators through an increased intrinsic growth rate, or by decreasing the enemy constraint. Both of these types of compensation have been observed in empirical studies of cooperators. [ABSTRACT FROM AUTHOR]

Recent field studies suggest that it is common in nature for animals to outlive their reproductive viability. Post-reproductive life span has been observed in a broad range of vertebrate and invertebrate species. But post-reproductive life span poses a paradox for traditional theories of life history evolution. The only commonly-cited explanation is the 'grandmother hypothesis', which is limited to higher, social mammals. We propose that post-reproductive life span evolves to stabilize population dynamics, avoiding local extinctions. Predator-prey and other ecosystem interactions tend to produce volatility that can create population crashes and local extinctions. Total fertility rates that exceed the ecosystem's recovery rate contribute to population overshoot, followed by collapse. These local extinctions may constitute a potent group selection mechanism, driving evolution toward controlled rates of population growth, even when there is a significant individual cost. In this paper, we consider the question: what life history characteristics support demographic homeostasis at the least cost to individual fitness? In individual-based evolutionary simulations, we find that reduction in fertility is sufficient to avoid population instabilities leading to extinction, but that life histories that include senescence can accomplish the same thing at a lower cost to individual fitness. Furthermore, life histories that include the potential for a post-reproductive period are yet more efficient at stabilizing population dynamics, while minimizing the impact on individual fitness. [ABSTRACT FROM AUTHOR]

Pollinators, like most other animals, often face a tradeoff between increasing food uptake and minimising predation. An earlier model suggests that social bees should be more likely than solitary bees to adopt riskier foraging strategies in order to increase food uptake. In this paper, we extend this model by studying the effect of body size, in addition to sociality, on the predation-intake rate tradeoff. When, following standard practice, we express the foraging strategies in terms of mortality probability and net food uptake, we find that body size should have no effect on the foraging strategies of solitary bees. Social bees, on the other hand, should change their foraging preferences according to their size. Small social bees should tend to maximise food uptake, and large social bees to minimise mortality rate. Mortality, however, is the product of two terms: the probability of suffering an attack and the probability of succumbing to it. Noting that larger bees are less susceptible to succumb to a predation attempt than smaller bees, model predictions change when foraging strategies are expressed in terms of exposure to predators. Following this second approach, exposure to predators should increase monotonically with body size in solitary bees. In social bees it should reach a minimum for medium-sized bees. We conclude that both bee body size and sociality should be considered when studying the effect of predators on resource use. [ABSTRACT FROM AUTHOR]

Our understanding of the dynamics of predator–prey systems has relied heavily on the use of models based on the standard Lotka–Volterra (LV) framework, dating back over 80 years. Although these models have been repeatedly analysed and refined since their initial inception, the way they describe the predator's growth rate has received surprisingly little attention; typically it is simply assumed that the predator's growth rate is linearly related to its ingestion rate according to a constant assimilation efficiency, e. However, for many consumers e is known to decrease at high prey densities. Models that ignore variable assimilation efficiencies overlook potentially important non-linearities, affecting the validity of predictions relating to conservation, invasion biology and pest control. Directly quantifying the relationship between e and prey abundance is, however, difficult. An alternative approach (the independent-response, IR, approach) is to not assume any direct link between the predator's functional response (the relationship between ingestion rate and prey abundance) and its growth response. This flexibility is invaluable when parameterising models from data; providing the model-fitting process is constrained to ensure that e never exceeds 1, this approach allows considerable insight into whether, and how, e varies with prey density. Here we examine the synergistic value of combining the IR and LV approaches. We illustrate these concepts through analysis of published functional and growth response data and show that, in many cases, e does vary with prey abundance. This paper is the first recognition that these two complementary approaches can be combined into a single framework that allows the relationship between a predator's functional and growth responses to emerge during the parameterisation process, thereby acting as a compromise between restrictive models that require this relationship to be defined a priori, and completely unrestrained models that allow assimilation efficiencies to exceed 1. [ABSTRACT FROM AUTHOR]

In this paper we explore variation in the predator-prey interaction between mink Mustela vison and muskrat Ondatra zibethicus across Canada based on 25 years of mink (predator) and muskrat (prey) data from the Hudson's Bay Company. We show that predator–prey interactions have stronger signatures in the west of Canada than in the east. In particular, we show that the observed phase plot trajectories of mink and muskrat rotate significantly clock-wise, consistent with predator–prey theory. We also investigate four phases of the mink muskrat interaction sequence (predator crash phase, prey recovery phase, etc.) and show that they are all consistent with a strong coupling in the west, whereas the presence of generalist predators and alternative preys can explain deviations from this pattern in the east. [ABSTRACT FROM AUTHOR]

The issue of predator limitation of vertebrate prey populations is contentious, particularly when it involves species of economic or conservation value. In this paper, we examine the case of raptor predation on upland passerines and waders in Scotland. We analysed the abundance of five wader and passerine species on an upland sporting estate in southern Scotland during an eight-year period when hen harrier, peregrine and merlin numbers increased due to strict law enforcement. The abundance of meadow pipit and skylark declined significantly during this time. Golden plover also showed a declining trend, whereas curlew increased significantly and there was a near significant increase in lapwings. Contrasting the local population trends of these species with trends on nearby areas revealed higher rates of decline for meadow pipit and skylark at the site where raptors increased, but no differences in trends for any of the three wader species. There was a negative relationship between the number of breeding harriers and meadow pipit abundance the same year and between total annual raptor numbers and meadow pipit abundance. Predation rates of meadow pipit and skylark determined from observations at harrier nests suggested that predation in June was sufficient to remove up to 40% of the June meadow pipit population and up to 34% of the June skylark population. This ‘quasi-natural’ experiment suggests that harrier predation limited the abundance of their main prey, meadow pipit, and possibly the abundance of skylark. Thus, high densities of harriers may in theory reduce the abundance of the prey species which determine their breeding densities, potentially leading to lower harrier breeding densities in subsequent years. We found no evidence to suggest that raptor predation limited the populations of any of the three wader species. We infer that concerns over the impact of natural densities of hen harriers on vulnerable upland waders are unjustified. [ABSTRACT FROM AUTHOR]

The relationship between density and area depends on local growth rates and the area-dependence of migration rates. These rates vary among taxa due to dispersal behaviour, plot productivity and natural enemy impact. Previous studies in aphids suggest that aphid densities are highest in patches of intermediate sizes, and lower in small and large patches. The suggested mechanism causing these patterns is that the dispersal behaviour in aphids creates a mixture of area- and perimeter-dependent migration rates. In this paper, we used these predictions to examine the additional consequences of nutrient availability and natural enemies on the density-area relationship. The derived predictions were compared to data from a system with three aphid species, a set of aphid parasitoids and generalist natural enemies, and at two levels of plant nutrient availability. We find that predictions from the model based only on dispersal and local growth agree with the temporal dynamics of density-area relationships for aphids in high nutrient patches. In patches with low nutrients, high parasitism rates appeared to cause a negative density-area relationship for aphids, thereby deviating from predictions driven by the aphids' dispersal behavior. Hence, the dispersal model with scale-dependent migration rates can provide a useful tool for understanding insect distribution in patch size gradients, but the relative importance of top-down effects can completely change with plot productivity. [ABSTRACT FROM AUTHOR]

We test whether the spatial distribution of birds within a habitat is determined by predation risk and also by interspecific competition. The work was carried out in a montane mixed forest of central Spain with four Parus species, the long-tailed tit ( Aegithalos caudatus) and the nuthatch ( Sitta europaea). Experimental feeders, that varied in their risk of predation, were used to control the effect of natural variations in food availability and quality on the habitat use patterns of different species. Tree gleaning passerines avoided feeding on dark inner forest places far from edges, distant from protective cover, outside the inner tree canopy and near the ground; they preferred deciduous, relatively clear forest plots. These effects remained invariable across years and weather conditions. There was a common pattern of selection of foraging locations by the four Parus species: proximity to cover and height above ground and over the lowest branches of the tree canopy positively influenced the use of feeding places. According to these patterns, the vigilance proportion of species was significantly higher when feeding far from cover than when birds were feeding near pine foliage. This pattern was also common for the four studied Parus species. Nevertheless, the interspecific dominance hierarchy of the species was positively correlated with the use of the safest feeders (feeders farther the ground and nearer from protective cover within tree canopy), being the converse with the most exposed ones. Therefore, the results of this paper demonstrate that the selection of feeding locations within habitat follows a pattern minimizing predation risk. Interspecific dominance hierarchies can lead to the exploitation of unfavourable risky patches by subordinate species. [ABSTRACT FROM AUTHOR]

Holling's type II functional response is a cornerstone of community ecology and coevolutionary theory. The so-called disc equation is the most widely used model of the type II response, yet thus far no robust experimental assessment has been achieved in any single system. Fundamental issues that remain to be assessed include whether the assumptions of the disc equation are fulfilled, whether the disc equation yields accurate estimates of predation-related individual traits, and whether differences in disc equation parameters can capture genetic variation in prey behaviour. This paper provides a rigorous approach to all of these questions. The functional response of the predatory mite Pergamasus crassipes on three genetically distinct clones of the springtail Folsomia candida was measured at six levels of prey density in controlled conditions where prey number and arena size were concomitantly manipulated. A crucial assumption of Holling's disc equation was fulfilled by maintaining a constant prey density for the entire experimental period of predation. The timing of each attack and capture, as well as the duration of the handling time, were recorded by constant observation. We contrasted three different methods to calculate functional response curves: (1) indirect estimation of the disc equation's parameters from the number of prey killed by the end of each experimental run; (2) direct estimation of the parameters via a unique protocol of constant observation; and (3) independently deriving a function based on direct measurements of encounter rate and attack success. The basic assumptions of the disk equation were globally fulfilled. Estimations of the functional response's parameters (type II) were remarkably congruent across approach (1) and (2). A single genetic effect was detected – the relationship between the encounter rate and prey density differed significantly between clones – whereas a direct comparison of functional response across clones failed to reveal genetic variation. [ABSTRACT FROM AUTHOR]

Predation is a fundamental ecological and evolutionary process that varies in space, and the avoidance of predation risk is of central importance in foraging theory. While there has been a recent growth of approaches to spatially model predation risk, these approaches lack an adequate mechanistic framework that can be applied to real landscapes. In this paper we show how predation risk can be decomposed into encounter and attack stages, and modeled spatially using resource selection functions (RSF) and resource selection probability functions (RSPF). We use this approach to compare the effects of landscape attributes on the relative probability of encounter, the conditional probability of death given encounter, and overall wolf and elk resource selection to test whether predation risk is simply equivalent to location of the predator. We then combine the probability of encounter and conditional probability of death into a spatially explicit function of predation risk following Lima and Dill's reformulation of Holling's functional response. We illustrate this approach in a wolf–elk system in and adjacent to Banff National Park, Alberta, Canada. In this system we found that the odds of elk being encountered by wolves was 1.3 times higher in pine forest and 4.1 times less in grasslands than other habitats. The relative odds of being killed in pine forests, given an encounter, increased by 1.2. Other habitats, such as grasslands, afforded elk reduced odds (4.1 times less) of being encountered and subsequently killed (1.4 times less) by wolves. Our approach illustrates that predation risk is not necessarily equivalent to just where predators are found. We show that landscape attributes can render prey more or less susceptible to predation and effects of landscape features can differ between the encounter and attack stages of predation. We conclude by suggesting applications of our approach to model predator–prey dynamics using spatial predation risk functions in theoretical and applied settings. [ABSTRACT FROM AUTHOR]

This paper reports the effects of food supply, predation and the interaction between them on the population dynamics of root voles,Microtus oeconomus, by adopting factorial experiments in field enclosures. This two-factor experiment proved the general hypothesis that food supply and predation had independent and additive effects on population dynamics of root voles. The experimental results proved the following predictions: (1) predation reduced population density and recruitment significantly; (2) food supply increased population density; (3) predation and food supply influenced spacing behavior of root voles separately and additively: Exposure to predation reduced long movements of root voles between trapping sessions; additional food supply reduced aggression level and home range size of root voles. Less movement of individuals that exposed to predators possibly reduced their opportunity of obtaining food and lessened population survival rate, which led population density to decrease. Smaller home range and lower aggression level could make higher population density tolerable. The interactive effect of predation and food on home range size was highly significant (P=0.0082<0.01). The interactive effect of food and predation on dispersal rate was significant (P<0.01). From the experimental results, we conclude that the external factors (predation, food supply) were more effective than internal factors (spacing behavior) in determining population density of root voles– under the most favorable external conditions (−P, +F treatment), the mean density and mean recruitment of root vole population was the highest; under the most unfavorable external conditions (+P,−F treatment), the mean density and mean recruitment of root vole population was the lowest. [ABSTRACT FROM AUTHOR]

Predation refugia can facilitate the coexistence of predators and prey within an ecosystem by weakening trophic links between the two. The marginal macrophytes of shallow lakes are used facultatively by zooplankton to escape fish predation, leading to the stabilisation of lentic food webs. Little is known about such a role for the marginal macrophytes of lotic systems. In this paper, we examine whether the marginal macrophytes of chalk streams help buffer the interaction between the freshwater shrimp,Gammarus pulexand a benthic fish predator,Cottus gobio, both characteristically abundant in such systems.Quantitative surveys were taken ofGammarusand bullheads in winter and summer in a southern English chalk stream. These indicated thatGammarusseasonally switched their habitat preference, from marginal macrophytes in summer, to midchannel habitats in winter. Bullheads exhibited an opposite trend, preferring midchannel habitats in summer and all habitats, particularly marginal macrophytes, in winter. LargeGammarusand precopula pairs were found almost exclusively in the margins in summer. This spatial separation betweenGammarusand bullheads in summer, though not in winter, was reflected in bullhead diets, as determined by gut analysis.In field manipulation experiments, bullhead presence was the strongest factor explaining the between-habitat distribution ofGammarusin both summer and winter, indicating that the habitat shift ofGammaruswas driven by the distribution of fish. Other abundant invertebrate taxa, includingAsellus, mayflies and chironomids, exhibited little avoidance of habitat patches of high bullhead density.We conclude that marginal macrophytes in chalk streams can potentially facilitate the coexistence of high densities of bothGammarusand bullheads by spatially separating predator and prey in summer. They may further allow large populations ofGammarusto persist in the presence of high bullhead density at stretch-wide spatial scales, by reducing the predation by bullheads of large breeding and newly born individuals ofGammarusin summer. [ABSTRACT FROM AUTHOR]

This paper examines the effect of different levels of protection from predation on feral house mice. Mice were contained in eight 50×50 m outdoor enclosures. Enclosures allowed access to a suite of freeliving vertebrate predators from the surrounding area, including feral foxes, feral cats and Australian raptors. A 10–15% cover of small, felled cypress pine trees was added in strips to low grassland to increase habitat complexity. Mice were not protected from predation when compared with low grassland pens, possibly because predators were able to focus their hunting activity in the strips. However, when felled trees were covered with wire netting, hence providing higher quality refuge, mouse populations achieved higher densities than in low grassland pens. A predator exclusion treatment was used to confirm the refuge effect was due to a reduction in the impact of predation. Survival rates under the different treatments were generally consistent with population level responses, with mice having lower survival in low grassland pens than in high refuge pens. This is the first study with mammals that confirms the importance of refuges from predators for prey populations. [ABSTRACT FROM AUTHOR]

Nest selection has important consequences for fitness in freshwater turtles, as nest predation is extremely high in most populations. However, nest predation has rarely been considered a major factor affecting nest site selection. Thermal qualities of a nest are often suggested as a factor influencing maternal choice of nest site because incubation temperature affects offspring performance and growth, as well as the sex ratio of the clutch in species with temperature dependent sex determination (TSD). Yet experimental manipulations of the nesting environment (habitat and threat) to test factors influencing maternal nest site selection in turtles are uncommon. In this paper, we show that nest site selection in an Australian turtle (Emydura macquarii ) with genetically determined sex determination (GSD) exists at two spatial scales, with predation as the major factor affecting the location of a nest. Females prefer to nest in areas where nest predation is minimal but when the risk of direct predation is increased, they trade-off minimising nest predation with survival by locating their nests closer to shore. However, experimentally reducing cover demonstrated that females prefer to nest in open areas, which are more common closer to shore. Hence females are forgoing preferred microhabitat to locate their nests away from shore to minimise nest predation. Despite a preference for open nesting areas, females exhibit similar repeatability of microenvironment selection to a North American species with TSD. Repeatability of nesting overstory vegetation in the North American turtle, Chrysemys picta, suggests that females may exert some control over the thermal qualities of the nests; a key assumption in theoretical models of the microevolution and adaptive significance of TSD in reptiles. Incubation temperature is one factor that may affect microhabitat preferences in both turtles but other factors (e.g. predation and soil moisture) affected by microhabitat may be... [ABSTRACT FROM AUTHOR]

Organisms often perceive predation risk through visual, auditory, or chemical cues that accompany or persist after an attack on other prey individuals. In this paper an argument is developed that suggests that it is adaptive for species that use such indirect cues to include conspecific density in the assessment of predation risk, and to respond to conspecific density by modifying phenotype (e.g. behavior, morphology of life history). A model based on this argument predicts that at equivalent (including negligible) indirect cue levels an organism should adopt less vulnerable phenotypes at lower conspecific density. Further, the phenotypic modifications to differences in conspecific density are predicted to be on the same order of magnitude as phenotypic responses to differences in predator density, to be more pronounced at higher indirect cue levels, and can be extended to responses to differences in the density of heterospecific species that share predators. This “risk assessment” mechanism is qualitatively different from other mechanisms, such as the dilution and “many eyes” effects that predict behavioral responses to conspecific density. If species use conspecific or heterospecific density to assess predation risk as predicted, there may be implications for the role and evolution of traits used to perceive conspecific and heterospecific densities, species aggregation, and population dynamics, and should be considered in the design of experiments of nonlethal effects of predators. [ABSTRACT FROM AUTHOR]

The costs and benefits associated with feeding in the vicinity of a predator should vary within and among species, depending on an individual's vulnerability to a predator. In this paper, we investigate how willingness to risk exposure to a predator in order to gain access to food is expressed within groups of fish. We provided groups of six individually marked brook sticklebacks (Culea inconstans ) and fathead minnows (Pimephales promelas ) with the opportunity to feed in safety, or in the presence of a single predator (walleye, Stizostedion vitreum ). Sticklebacks and fathead minnows are commonly found in the same locations at the same time, but sticklebacks also possess armour and spines that provide defence against some predators. Despite this morphological variation, patterns of individual behaviour were consistent between species. While feeding close to the predator, there was a positive relation between the size of the individual and the proportion of food consumed. No relation existed on the side farthest from the predator. These data suggest that fish may risk exposure to predators to exploit size-related differences in vulnerability to gain a competitive advantage for access to food. [ABSTRACT FROM AUTHOR]

Well‐established ecological equations such as logistic growth may carry implicit assumptions that are not immediately obvious. When such equations are adapted for a different context, missing awareness of their hidden assumptions can confound our conclusions. We demonstrate how this has happened in predator–prey models with rapid adaptation of prey defense to variable predation risk, where costs of defense typically manifest as a growth‐defense tradeoff. Assuming logistic prey growth, this tradeoff is often implemented as a reduced intrinsic growth rate, while the carrying capacity is unaffected. We show that this assumption is not only extremely ecologically unrealistic, but also results in highly problematic model behavior and destroys any potential for eco‐evolutionary or biomass‐trait feedbacks. To reconcile the problematic results of this assumption with its ubiquity in existing models with rapid adaptation, we conducted a literature survey of models on prey adaptation or predator–prey co‐adaptation. This reveals that many models, despite describing a tradeoff affecting only the intrinsic growth rate, do incorporate an additional cost affecting the carrying capacity, but in a way that is implicit and not acknowledged. It is this cost that drives the famous feedbacks between defense adaptation and predator–prey dynamics. Finally, we discuss the implications for existing theory on eco‐evolutionary dynamics, and provide guidelines for implementing growth‐defense tradeoffs in a more realistic way. [ABSTRACT FROM AUTHOR]

Phenotypic plasticity has primarily been studied in the context of adaptation to environmental fluctuations and its underlying genetic mechanisms. However, its impact on competition and coexistence has rarely been addressed. In this paper we analyzed the ecological and evolutionary implications of phenotypic plasticity in diel vertical migration of competing, physiologically distinguishable, Daphnia populations. We developed a model that evaluates the competitive strength of daphnids which are food limited and which face predation. Competitive strength is assessed by a population's ability to invade and defend a previously established site. Phenotypically plastic individuals were assumed to choose an evolutionarily stable migration strategy at any time during the invasion process. We found plasticity to increase a population's competitive ability and in special cases to support coexistence of similar populations. Including community structure in analyzing the adaptive value of phenotypic plasticity reveals aspects thatare not directly inferable from isolated population models. Hence, selection for plasticity may be more widespread than generally expected. [ABSTRACT FROM AUTHOR]

During the fourth stage of larval development the American lobster (Homarus americanus) leaves the plankton and becomes benthic. Before final settlement lobsters sample different substrates which may be accepted or rejected. Upon rejection the lobster returns to the planktonbefore sampling another substrate. In this paper we present a model of the substrate selection behavior of settling lobsters using dynamic optimization techniques. The model examines the role of substrate quality and availability, postlarval testing of substrates, and mortality associated with testing substrates, upon the decision to accept or reject the substrates sampled and predicts the eventual importance of each substrate in the recruitment of lobsters to reproductive age.Finally we apply the model using recent data on long-term survival of lobsters in the field. The model predicts that the high quality substrate (cobble) accounts for most of the adult lobster population, inspite of the much greater abundance of other, more marginal, substrates. [ABSTRACT FROM AUTHOR]

The basic ideal free model (all individuals are alike, omniscient, and free to move between patches) predicts the spatial distribution ofanimals in a patchy environment. The notion that ideal free models for individuals that differ in competitive ability, predict a distribution that deviates basically from the ideal free distribution of equal competitors is widespread. In this paper I present a distribution model in which differences in competitive ability among individuals are assumed. The model, however, predicts a distribution equal to the ideal free distribution of competitors that are all alike. The model belongs to a class of models in which an individual's payoff depends on the sum of the amount of interference it experiences from each of the competitors in the patch. The amount of interference that a competitor experiences from another competitor can vary. The interference relationship between all pairs of individuals is presented in the formof an 'interference matrix'. Several possible interference matrices are presented. All models assume that an individual's payoff will never increase with increasing numbers of competitors in the patch, and that an animal will experience more interference when surrounded withrelatively strong competitors than when surrounded with weaklings. Ishow that models which have previously predicted distributions radically different from the ideal free distribution of equal competitors,i.e. the truncated phenotype distribution, have made the same claims(i.e. that an individual's payoff will never increase with increasing numbers of competitors) for the wrong reasons. [ABSTRACT FROM AUTHOR]

The searching efficiency of predators depends on the balance between the adaptations of the predator and the counter‐adaptations of the prey. In this evolutionary race, the prey should normally have the upper hand, as it can perform tradeoffs between efficiency in resource use and ability to avoid predators. In terrestrial predator–herbivore systems, however, the huge difference in food quality between prey and predators seems to give predators an advantage. In productive terrestrial ecosystems, predators thus chronically overexploit herbivores, i.e. regulate them at densities far below the point of maximum sustainable yield. Assuming type II functional response, this should result in violent limit cycle dynamics. In reality, however, such cycles are only common at high latitudes, whereas the herbivory‐based food webs of species‐rich ecosystems at middle and low latitudes are characterized by asymptotic dynamics, where numerical changes only occur in response to external forcing. One way or another, diversity thus seems to beget stability in terrestrial grazing webs. We propose that strong, donor‐controlled energy flows from the detritus web and directly from plants to predators are the key for the prevalence of asymptotic dynamics at middle and low latitudes. These flows support generalists with type III functional response and, therefore, a capacity to curb budding outbreaks at an early stage. The ongoing extinction wave could critically weaken these stabilizing interactions, which could destabilize currently stable food webs. and result in violent limit cycle dynamics in ecosystems, where the dominating species have evolved under asymptotic dynamics. This could cause secondary extinctions and inflict large economic losses. Keywords: extinction, food webs, limit cycles, overexploitation, searching efficiency, stability [ABSTRACT FROM AUTHOR]

Predation risk causes prey to react in numerous ways, from life history changes to shifts in habitat. These responses give some insight into how different types of predators affect prey, but prey responses are often not comparable across taxa and experimental systems. Metabolism is a ubiquitous trait among living organisms, which offers a way to examine predator effects and create generalizable outcomes. We examined metabolic responses of terrestrial and aquatic prey from three antipredator functional groups under varied contexts of predator cues. We found that constitutively defended prey did not exhibit metabolic responses to any type of predator cues, while deimatic and freeze‐flight prey exhibited metabolic responses that were dependent on both the cue type and predator hunting mode. Consistent with previous studies on nonconsumptive effects, we also found that ambush predators elicited a metabolic response while active predators did not. We propose that future work on this topic should continue to take a metabolic approach as a unified, scalable response variable to the sensory ecology of nonconsumptive effects, while identifying additional systems that can evaluate more fully both predator hunting mode and prey antipredator defenses. [ABSTRACT FROM AUTHOR]

Quantifying the cumulative effects of stressors on individuals and populations can inform the development of effective management and conservation strategies. We developed a Bayesian state–space model to assess the effects of multiple stressors on individual survival and reproduction. In the model, stressor effects on vital rates are mediated by changes in underlying health, allowing for the comparison of effect sizes while accounting for intrinsic factors that might affect an individual's vulnerability and resilience. We applied the model to a 50‐year dataset of sightings, calving events and stressor exposure of critically endangered North Atlantic right whales Eubalaena glacialis. The viability of this population is threatened by a complex set of stressors, including vessel strikes, entanglement in fishing gear and fluctuating prey availability. We estimated that blunt and deep vessel strike injuries and severe entanglement injuries had the largest effect on the health of exposed individuals, reinforcing the urgent need for mitigation measures. Prey abundance had a smaller but protracted effect on health across individuals, and estimated long‐term trends in survival and reproduction followed the trend of the prey index, highlighting that long‐term ecosystem‐based management strategies are also required. Our approach can be applied to quantify the effects of multiple stressors on any long‐lived species where suitable indicators of health and long‐term monitoring data are available. [ABSTRACT FROM AUTHOR]

Biodiversity describes the variety of organisms on planet earth. Ecologists have long hoped for a synthesis between analyses of biodiversity and analyses of biotic interactions among species, such as predation, competition and mutualism. However, it is often unclear how to connect details of these interactions with complex modern analyses of biodiversity. To resolve this gap, we propose a unification of models of biotic interactions and measurements of diversity. We show that analyses of biodiversity obscure details about biotic interactions. For example, identical changes in biodiversity can arise from predation, competition or mutualism. Our approach indicates that traditional models of community assembly miss key facets of diversity change. Instead, we suggest that analyses of diversity change should focus on partitions, which measure mechanisms that directly shape changes in diversity, notably species level selection and immigration, rather than traditional analyses of biotic interactions. [ABSTRACT FROM AUTHOR]

Despite considerable study of population cycles, the striking variability of cycle periods in many cyclic populations has received relatively little attention. Mathematical models of cyclic population dynamics have historically exhibited much greater regularity in cycle periods than many real populations, even when accounting for environmental stochasticity. We contend, however, that the recent focus on understanding the impact of long, transient but recurrent epochs within population oscillations points the way to a previously unrecognized means by which environmental stochasticity can create cycle period variation. Specifically, consumer–resource cycles that bring the populations near a saddle point (a combination of population sizes toward which the populations tend, before eventually transitioning to substantially different levels) may be subject to a slow passage effect that has been dubbed a 'saddle crawlby'. In this study, we illustrate how stochasticity that generates variability in how close predator and prey populations come to saddles can result in substantial variability in the durations of crawlbys and, as a result, in the periods of population cycles. Our work suggests a new mechanistic hypothesis to explain an important factor in the irregular timing of population cycles and provides a basis for understanding when environmental stochasticity is, and is not, expected to generate cyclic dynamics with variability across periods. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Perceived predation risk varies in space and time creating a landscape of fear. This key feature of an animal's environment is classically studied as a species‐specific property. However, individuals differ in how they solve the tradeoff between safety and reward and may, hence, differ consistently and predictively in perceived predation risk across landscapes. To test this hypothesis, we quantified among‐individual differences in boldness and activity and exposed behaviourally phenotyped male bank voles Myodes glareolus individually to two different experimental landscapes of risks in large outdoor enclosures and provided resources as discrete food patches. We manipulated perceived predation risk via vegetation height between 2 and > 30 cm and quantified patch use indirectly via RFID‐logging and giving‐up densities. We statistically disentangled among‐individual differences in microhabitat use from spatially varying perceived risk, i.e. landscape of fear. We found that individuals varied in mean vegetation height of their foraging microhabitats and that this microhabitat selection matched the intrinsic individual differences in perceived risk. As predicted by the patch use model, all individual's perceived higher risks when foraging in lower vegetation. However, individuals differed in their reaction norm slopes of perceived risk to vegetation height, and these differences in slopes were consistent across two different landscapes of risks and resources. We interpret these results as evidence for individual landscapes of fear, which could be predicted by among‐individual differences in activity and boldness. Since perceived predation risk affects when and where to forage, among‐individual differences in fear responses could act as a mode of intraspecific niche complementarity (i.e. individual niche specialization), help explain behavioural type by environment correlations, and will likely have cascading indirect effects on lower trophic levels. [ABSTRACT FROM AUTHOR]

Spatial heterogeneity in ecological systems can result from animal‐driven top–down processes, but despite some theoretical attention, the emergence of spatial heterogeneity 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 feedbacks 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 homogenize 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. [ABSTRACT FROM AUTHOR]

In the absence of environmental heterogeneity, spatial variation among local communities can be mostly attributed to random dispersal, demographic stochasticity and species interactions causing historical contingency in colonization (e.g. priority effects). The consequences of demographic stochasticity and random dispersal are highly dependent on community size, regional richness and local richness, which, along with historical contingency can be strongly affected by spatial isolation and the presence of predators. Here, we tested whether and how the presence of a generalist predatory fish and spatial isolation can change spatial community variability in artificial ponds by manipulating the presence/absence of fish (redbreast tilapia) at three different distances from a source wetland. We then used null models to compute how much the observed community variability within treatments deviates from the expected from randomly reassembled communities (i.e. beta‐deviation). We found that spatial isolation can have both negative and positive effects on community variability, and their importance may depend on the presence of predatory fish. Negative effects likely occurred because predatory insects cannot always successfully colonize highly isolated ponds, causing the abundance of herbivores and detritivores to increase, consequently increasing community size, which is known to decrease the importance of demographic stochasticity. However, when fish are absent, the more isolated communities exhibit more community variability than is expected from random community assembly. We believe that such an increase in variability is most likely due to an increase in the importance of historical contingency in colonization, generating more distinct communities in isolated ponds. Such effects were absent in the presence of generalist predatory fish, likely because fish prevented any early colonizing taxa from becoming too abundant. Our findings show that the presence of generalist predators can change how community variability responds to spatial isolation. [ABSTRACT FROM AUTHOR]

Data rarely are available to address the level of predation risk faced by diving animals in different parts of the water column. Consequently, most published research on diving behaviour implicitly assumes – like the proverbial ostrich – that ‘unseen’ predators are functionally unimportant. We argue that failure to consider diving in a predation risk framework may have precluded many insights into the ecology of aquatic foragers that breathe air. Using existing literature and a simple model, we suggest that fear from submerged predators in several systems might be influencing patch residence time, and therefore the duration of other dive cycle components. These analyses, along with an earlier model of predation risk faced by diving animals at the surface, suggest that dive cycle organisation can be modified to increase safety from predators, but only at the cost of reduced energy gain. Theoretical arguments presented here can seed hypotheses on factors contributing to population declines of diving species. For instance, adjustments to the dive cycle that reduce predation risk might be unaffordable if resources are scarce. Thus, if animals are to avoid imminent starvation or substantial loss of reproductive potential, resource declines might indirectly increase predation rates by limiting the extent to which dive cycles can deviate from those that would maximize energy gain. We hope that ideas presented in this paper stimulate other researchers to further develop theory and test predictions on how predation risk might influence diving behaviour and its ecological consequences. [ABSTRACT FROM AUTHOR]

Harvesting may drive body downsizing along with population declines and decreased harvesting yields. These changes are commonly construed as consequences of direct harvest selection, where small‐bodied, early‐reproducing individuals are immediately favoured. However, together with directly selecting against a large body size, harvesting and body downsizing alter many ecological features, such as competitive and trophic interactions, and thus also indirectly reshape natural selection acting back on body sizes through eco‐evolutionary feedback loops (EEFLs). We sketch plausible scenarios of simple EEFLs in which one‐dimensional, density‐dependent natural selection acts either antagonistically or synergistically with direct harvest selection on body size. Antagonistic feedbacks favour body‐size stasis but erode genetic variability and associated body‐size evolvability, and may ultimately impair population persistence and recovery. In contrast, synergistic feedbacks drive fast evolution towards smaller body sizes and favour population resilience, but may have far‐reaching bottom–up or top–down effects. We illustrate the further complexities resulting from multiple environmental feedbacks using a co‐evolving predator–prey pair, in which case outcomes from EEFLs depend not only on population densities, but also on whether prey sit above or below the optimal predator/prey body‐size ratio, and whether prey are more or less evolvable than their predators. EEFLs improve our ability to understand and predict nature's response to harvesting, but their integration into the research agenda will require a full consideration of the effects and dynamics of natural selection. [ABSTRACT FROM AUTHOR]

Plastic and evolutionary changes in traits related to biotic interactions are crucial for the local persistence of populations under global warming. Yet, how acute and developmental thermal plasticity evolve and shape predation rates has been poorly studied, especially in the context of latitude‐driven thermal evolution. A powerful predictive framework is given by the climatic variability hypothesis (CVH) stating that thermal plasticity and acclimation capacity evolve to be higher in high‐latitude populations because these are exposed to higher thermal seasonal variability. We tested the CVH for predation rates and evaluated if the support for the CVH depended on the type of plasticity and acclimation metric. We examined effects of developmental temperature (20 and 24°C) and acute changes in mean and extreme temperatures (20, 24 and 32°C) on the predation rates of high‐ and low‐latitude populations of a predatory aquatic insect, the damselfly Ischnura elegans. We documented opposing and interactive effects between developmental and acute temperatures, which urges caution when using thermal performance curves to forecast the impact of global warming on biotic interactions. Predation rates were higher in low‐latitude than high‐latitude predators, especially at the warmer developmental and test temperatures, suggesting thermal adaptation to the higher low‐latitude temperatures. The latitudinal patterns in acute and developmental plasticities differed, providing mixed support for the CVH. Moreover, there was no latitudinal pattern in post‐acclimation thermal sensitivity, indicative of perfect thermal compensation in predators from both latitudes. Strikingly, the acclimation capacity leading to perfect thermal compensation was ~6 times higher in high‐latitude than in low‐latitude predators. Our study provides new insights into the climatic variability hypothesis (CVH) by documenting that its support is critically dependent on the type of plasticity and acclimation metric used. [ABSTRACT FROM AUTHOR]

Disturbance plays a key role in ecological structure and function. Two important and often studied components of disturbance are frequency and magnitude. Despite the potential for non‐linear interactions between frequency and magnitude, their effects are often assumed to combine in a linear manner. Additionally, studies of disturbance have mainly examined effects on species diversity and competitive interactions within a single trophic level, with less focus on exploitative interactions across trophic levels. Furthermore, while the effects of disturbance are often viewed in terms of reducing population abundance, disturbances can also alter demographic processes, 'indirectly' changing abundances. We analyzed several classic dynamic models of species interactions to examine the effects of varying disturbance frequency and magnitude on population persistence in predator–prey and competition systems. Our analysis revealed the potential for non‐linear interactions between frequency and magnitude and their effect on population persistence. Effects differed depending on the form of population dynamics and whether disturbance affected abundance or demographic rates. It is critical to management efforts aiming to improve chances of population persistence to further understand the effects of varying disturbances on interacting populations. [ABSTRACT FROM AUTHOR]

Predicting the ecological and evolutionary trajectories of populations in multispecies communities is one of the fundamental challenges in ecology. Many of these predictions are made by scaling patterns observed from pairwise interactions. Here, we show that the coupling of ecological and evolutionary outcomes is likely to be weaker in increasingly complex communities due to greater chance of life‐history trait correlations. Using model microbial communities comprising a focal bacterial species, Bacillus subtilis, a bacterial competitor, protist predator and phage parasite, we found that increasing the number of enemies in a community had an overall negative effect on B. subtilis population growth. However, only the competitor imposed direct selection for B. subtilis trait evolution in pairwise cultures and this effect was weakened in the presence of other antagonists that had a negative effect on the competitor. In contrast, adaptation to parasites was driven indirectly by correlated selection where competitors had a positive and predators a negative effect. For all measured traits, selection in pairwise communities was a poor predictor of B. subtilis evolution in more complex communities. Together, our results suggest that coupling of ecological and evolutionary outcomes is interaction‐specific and generally less evident in more complex communities where the increasing number of trait correlations could mask weak ecological signals. [ABSTRACT FROM AUTHOR]

Most studies on eco‐evolutionary feedbacks concern the influence of abiotic factors, or predator–prey and host–parasite interactions, while studies involving sexual interactions are lagging behind. This is at odds with the potential of these interactions to engage in such processes. Indeed, there is now ample evidence that sexual selection is affected by ecological change and that sexually selected traits can evolve rapidly, which may modify the ecological context of populations, and thus the selection pressures they will be exposed to. Here we review evidence for such eco‐evolutionary processes. We discuss examples of eco‐evolutionary change in an attempt to understand the challenges related with identifying and characterizing such processes. In particular, we focus on the challenges associated with accurately identifying the components of the feedback as well as their causal relation. Finally, we evaluate scenarios where understanding eco‐evolutionary feedbacks of sexual selection may help us appreciate the effects of sexual selection in shaping evolutionary processes. [ABSTRACT FROM AUTHOR]

In fragmented landscapes, the reduced connectivity among patches drives the evolution of movement strategies through an increase of transience costs. Reduced movements may further alter heterogeneity in biotic and abiotic conditions experienced by individuals. The joint action of local conditions and matrix permeability may shape emigration decisions. Here, we tested the interactive effects of predation risk and matrix permeability on movement propensity, movement costs and movers' phenotype in the common toad Bufo bufo. In a full‐crossed experimental design, we assessed the movement propensity of juveniles in three connectivity treatments (from poorly to highly permeable matrix), with or without predation risk in their living patch. We also assessed the relationships between movement propensity and morphological traits (i.e. body and leg length) and how it affected the movement cost (i.e. mass loss). Movement propensity increased in presence of predation risk, while matrix permeability had no effect. However, matrix permeability interacted with predation risk to influence movers' phenotype and the physiological cost they endured while moving. In particular, a well‐known movement syndrome in toads (i.e. movement propensity positively related to longer legs) depended on the interaction between matrix permeability and predation risk and resulted in differences in mass loss among matrix types. Movers lost more mass on average than residents except when they also displayed longer legs or when they crossed the most permeable matrix in the presence of predation risk. Our results show that matrix permeability shapes the physiological cost of dispersal by changing the identity of individuals moving away from local conditions. As the movers' phenotype can importantly alter (meta)population dynamics, context‐dependency of dispersal syndromes should be considered in studies predicting the functioning of human‐altered natural systems. [ABSTRACT FROM AUTHOR]

Prey often reduce predation risk at the cost of lower resource intake. The cumulative effects of such tradeoffs can alter resource allocation, demography and evolutionary processes. We show how the accumulation of risk effects reduces the growth rate of wild North American porcupines Erethizon dorsatum, and simulate three evolutionary responses related to lifetime reproductive success. Individual porcupines experiencing predation risk from fishers Pekania pennanti grew slower and gave birth to fewer offspring. Simulations show that predation risk alone can lead to population declines, and that a female can replace herself by investing more energy into reproduction or adult survival; females that only invest energy in juvenile survival cannot. We show that the accumulation of predation risk can reduce lifetime reproductive success in natural ecosystems. Estimating the contribution of predation risk, and how evolutionary responses can mediate consequences associated with predation risk, is necessary to understand the evolution of predator–prey systems. [ABSTRACT FROM AUTHOR]

Most communities are structured not by a single process but by some combination of top–down, bottom–up and supply–side (i.e. juvenile recruitment) factors. However, establishing how multiple processes interact remains a fundamental challenge. For example, the recruitment, growth, and mortality of estuarine species can vary along the steep and numerous environmental and biological gradients typical of these habitats, but the relative importance of those gradients is generally unknown. We took a novel approach to this question by coupling long‐term field observations of the Olympia oyster Ostrea lurida in a central California estuary with a state–space integral projection model. This approach revealed that the most parsimonious description of oyster population dynamics involved spatial variation in growth and adult mortality – but not juvenile mortality – as well as spatiotemporal variation in recruitment. These patterns match the available short‐term estimates of each of those processes from field studies, and reveal a synthetic view of oyster population dynamics. Larval recruitment has an interannual 'boom and bust' pattern, and during good recruitment years most larvae settle in the inner bay where water residence time is highest. Adult oyster mortality is also highest in the inner bay, where several invasive predators are abundant and lowest in the mid‐bay, where oyster growth is greatest (due to bottom–up factors), likely leading to a size refuge from native predators. Surprisingly, juvenile mortality was constant across the bay, possibly because of a lack of size refuge from native and invasive predators. Our research approach represents an important advance in disentangling the contributions of spatio–temporal variation in top–down, bottom–up and supply–side forces to the dynamics of populations with open recruitment. [ABSTRACT FROM AUTHOR]

Changes in the strength of trophic cascades over time have been associated with dramatic shifts in community structure and function. However, the pattern, process, and potential underlying mechanism of temporal variation in trophic cascades remains relatively unexplored. A top–down trophic cascade has been documented for the effects of predacious weaver ants Oecophylla smaragdina on the success of fig tree Ficus racemosa seed production. Ants cause high mortality of non‐pollinating fig wasps Sycophaga mayri that parasitize fruits, leading to greater success for the pollinating fig wasp–fig tree mutualists. Here, using a design in which pairs of branches were selected on a tree, and ants were excluded from one of each pair, we quantified the magnitude of the trophic cascade in the cool–dry, hot–dry and rainy (hot–wet) seasons in Xishuangbanna, southwest China. We also recorded the daily behavioral dynamics of ants and fig wasps in different seasons and analyzed the correlation between behavioral, activity and trophic cascade strength. We found that the strength of the trophic cascade was strong in the hot–dry season, diminished in the rainy season and disappeared in the cool–dry season in this system. The strength of species interactions between ants and non‐pollinating fig wasps, is positively correlated with trophic cascade strength, indicating that trophic cascade strength is determined by a top–down process when the community is well established. Moreover, because pollinating fig wasps, Ceratosolen fusciceps, play a central role in the establishment of fig wasp communities, when C. fusciceps wasps are absent, the community quickly disassembles as is the case in the cool–dry season. In summary, the strength of the trophic cascade is triggered by top–down processes, however, the occurrence of the trophic cascade is determined by a keystone species that plays a central role in assembly of the community. [ABSTRACT FROM AUTHOR]