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A narrative in ecology is that prey modify traits to reduce predation risk, and the trait modification has costs large enough to cause ensuing demographic, trophic and ecosystem consequences, with implications for conservation, management and agriculture. But ecology has a long history of emphasising that quantifying the importance of an ecological process ultimately requires evidence linking a process to unmanipulated field patterns. We suspected that such process-linked-to-pattern (PLP) studies were poorly represented in the predation risk literature, which conflicts with the confidence often given to the importance of risk effects. We reviewed 29 years of the ecological literature which revealed that there are well over 4000 articles on risk effects. Of those, 349 studies examined risk effects on prey fitness measures or abundance (i.e., non-consumptive effects) of which only 26 were PLP studies, while 275 studies examined effects on other interacting species (i.e., trait-mediated indirect effects) of which only 35 were PLP studies. PLP studies were narrowly focused taxonomically and included only three that examined unmanipulated patterns of prey abundance. Before concluding a widespread and influential role of predation-risk effects, more attention must be given to linking the process of risk effects to unmanipulated patterns observed across diverse ecosystems.

Defensive traits are hypothesized to benefit prey by reducing predation risk from a focal predator but come at a cost to the fitness of the prey. Variation in the expression of defensive traits is seen among individuals within the same population, and in the same individual in response to changes in the environment (i.e., phenotypically plastic responses). It is the relative magnitude of the cost and benefit of the defensive trait that underlies the defensive trait expression and its consequences to the community. However, whereas the cost has received much attention in ecological research, the benefit is seldom examined. Even in a defensive trait as extensively studied as vigilance, there are few studies of the purported benefit of the behavior, namely that vigilance enhances survival. We examined whether prey vigilance increased survival and quantified that benefit in a natural system, with white‐tailed deer (Odocoileus virginianus) experiencing unmanipulated levels of predation risk from Florida panther (Puma concolor coryi). Deer that spent more time vigilant (as measured by head position using camera trap data) had a higher probability of survival. Indeed, an individual deer that was vigilant 75% of the time was more than three times as likely to be killed by panthers over the course of a year than a deer that was vigilant 95% of the time. Our results therefore show that within‐population variation in the expression of a defensive trait has profound consequences for the benefit it confers. Our results provide empirical evidence supporting a long‐held but seldom‐tested hypothesis, that vigilance is a behavior that reduces the probability of predation and quantifies the benefit of this defensive trait. Our work furthers an understanding of the net effects of a trait on prey fitness and predator–prey interactions, within‐population variation in traits, and predation risk effects. [ABSTRACT FROM AUTHOR]

Human activities catalyse risk avoidance behaviours in wildlife across taxa and systems. However, the broader ecological significance of human‐induced risk perception remains unclear, with a limited understanding of how phenotypic responses scale up to affect population or community dynamics. We present a framework informed by predator–prey ecology to predict the occurrence of non‐consumptive effects (NCE) and trait‐mediated indirect effects (TMIE) of anthropogenic disturbances. We report evidence from a comprehensive review of the different types of human‐induced behavioural and physiological phenotypic changes and their influence on vital rates and population parameters in wildlife. Evidence for human‐induced NCEs and TMIEs is mixed, with half of published studies finding a relationship between human activities, phenotypic change and population outcomes. The net effects of anthropogenic NCEs and TMIEs depend on the mismatch between the phenotypic response and the lethality of human activity. However, strong research biases in taxa, systems, human disturbance types and demographic measures prevent unified inference about the prevalence of population responses to human activities. Coexistence with and conservation of wildlife requires additional research linking human‐induced phenotypic change to population and community outcomes. [ABSTRACT FROM AUTHOR]

Predators can directly affect prey populations both through predation (consumption of prey) and risk‐induced trait responses (RITRs) that reduce predation risk but are often associated with a fitness cost. Thousands of studies make clear that RITRs (also termed anti‐predator or defensive traits) including changes in behavior, morphology, and life history, are employed by numerous taxa across diverse ecological systems, and there is large variation in their magnitude. A natural goal is to elucidate the species and circumstances for which and to what magnitude RITRs are expected. A candidate hypothesis is that prey species that experience higher mortality from a predator will exhibit a higher RITR. This hypothesis is an intuitive extension of the fact that invulnerable animals are not expected to exhibit an RITR, while vulnerable species are. We present an example that clarifies why this relationship is not always expected and when it is expected. Other factors may influence the level of the RITR leading to the possibility that a positive relationship is not expected. We elucidate this problem using a mesocosm experiment with a fish–cladoceran system in which there is large variability in the predation rate on different cladoceran species. Results not only did not show a positive relationship, but rather a negative trend between predation rate and the RITR. In fact, highly preyed upon taxa did not respond, while the least preyed upon taxa had the largest responses. These results clarify how the level of predation risk interacts with many factors to determine the RITR of prey. [ABSTRACT FROM AUTHOR]

We evaluated predation by the invasive invertebrate planktivore Bythotrephes longimanus on a Lake Michigan prey assemblage as a function of light intensity. Daphnia mendotae was the only prey type significantly reduced and light intensity strongly affected this reduction. Specifically, Bythotrephes consumption of D. mendotae was not detected under low light intensity (100 [micro]mol-[m.sup.-2.][s.sup-1]) at which point Bythotrephes ingestion rate was 2.3 Daphnia per hour. These results indicate that Bythotrephes predation is more sensitive to light than previously thought, a discrepancy that can be explained after considering the ability of D. mendotae to detect Bythotrephes' hydromechanic disturbance. The observed effect of light intensity on Bythotrephes predation is more like that of planktivorous fish than that of other previously studied invertebrate planktivores. Our findings elucidate the role that Bythotrephes plays in the food web and provide a novel explanation for its tendency to invade lakes of high water clarity. The importance of light-dependent predation found here may extend to other visually oriented predatory cladocerans. Nous evaluons la predation par l'invertebre envahissant planctonophage Bythotrephes longimanus sur un ensemble de proies du lac Michigan en fonction de l'intensite lumineuse. Daphnia mendotae est le seul type de proie a subir une reduction significative et l'intensite lumineuse affecte fortement cette reduction. En particulier, on ne decele pas de consommation de D. mendotae par Bythotrephes aux faibles intensites lumineuses (100 mmol.[m.sup.-2.][s.sup-1]) et a ce point, le taux d'ingestion de Bythotrephes est de 2,3 Daphnia par heure. Ces resultats indiquent que la predation de Bythotrephes est plus sensible a la lumiere qu'on ne le croyait anterieurement, un ecart qui peut s'expliquer si l'on tient compte de la capacite de D. mendotae a detecter la perturbation hydraulique causee par Bythotrephes. L'effet de l'intensite lumineuse observe sur la predation chez Bythotrephes ressemble plus a celui qui se produit chez les poissons planctonophages que chez les autres invertebres planctonophages etudies. Nos observations mettent en lumiere le role joue par Bythotrephes dans le reseau alimentaire et apportent une explication inedite a la tendance qu'a Bythotrephes a envahir les lacs a eau tres claire. L'importance de la predation dependante de la lumiere s'applique peut-etre aussi a d'autres cladoce res predateurs a orientation visuelle. [Traduit par la Redaction], Introduction Light can strongly influence the composition and dynamics of communities in aquatic systems (Interlandi and Kilham 2001; Wissel et al. 2003; Sornes and Aksnes 2006). One mechanism underlying this [...]

For example, the containment method for degrees of freedom gives the exact degrees of freedom when the design is balanced, i.e., all random effects in the model are nested and sample sizes within each group defined by the random effects are equal. More simply, using the so-called containment method for degrees of freedom also reduced the type I error rate. Recently, Nakagawa et al. (2021) provided a timely and insightful comment to our paper on statistical methods for non-independent data in ecological meta-analyses (Song et al. 2020). [Extracted from the article]