The many faces of fear: a synthesis of the methodological variation in characterizing predation risk

Abstract

Predators affect prey by killing them directly (lethal effects) and by inducing costly antipredator behaviours in living prey (risk effects). Risk effects can strongly influence prey populations and cascade through trophic systems. A prerequisite for assessing risk effects is characterizing the spatiotemporal variation in predation risk. Risk effects research has experienced rapid growth in the last several decades. However, preliminary assessments of the resultant literature suggest that researchers characterize predation risk using a variety of techniques. The implications of this methodological variation for inference and comparability among studies have not been well recognized or formally synthesized. We couple a literature survey with a hierarchical framework, developed from established theory, to quantify the methodological variation in characterizing risk using carnivore-ungulate systems as a case study. Via this process, we documented 244 metrics of risk from 141 studies falling into at least 13 distinct subcategories within three broader categories. Both empirical and theoretical work suggest risk and its effects on prey constitute a complex, multi-dimensional process with expressions varying by spatiotemporal scale. Our survey suggests this multi-scale complexity is reflected in the literature as a whole but often underappreciated in any given study, which complicates comparability among studies and leads to an overemphasis on documenting the presence of risk effects rather than their mechanisms or scale of influence. We suggest risk metrics be placed in a more concrete conceptual framework to clarify inference surrounding risk effects and their cascading effects throughout ecosystems. We recommend studies (i) take a multi-scale approach to characterizing risk; (ii) explicitly consider 'true' predation risk (probability of predation per unit time); and (iii) use risk metrics that facilitate comparison among studies and the evaluation of multiple competing hypotheses. Addressing the pressing questions in risk effects research, including how, to what extent and on what scale they occur, requires leveraging the advantages of the many methods available to characterize risk while minimizing the confusion caused by variability in their application.

Safety first: seasonal and diel habitat selection patterns by red deer in a contrasted landscape

“…Animal space‐use patterns result from the need to balance access to limiting resources with avoidance of competition (Vanak et al ., ), predation risk (Thaker et al ., ; Wirsing & Ripple, ; Lone et al ., ; Moll et al ., ), or human disturbance (Ciuti et al ., ; Kuijper et al ., ; Stabach et al ., ; Bötsch, Tablado & Jenni, ; Müller et al ., ; Smith et al ., ). Spatially heterogeneous landscapes provide solutions to the forage‐safety trade‐off when animals can access risky but energetically rewarding patches, or safer patches with lower resources abundance or quality (landscape of fear) (Bjørneraas et al ., ; Basille et al ., ; Padié et al ., ; Filla et al ., ).…”

Interspecific prey neighborhoods shape risk of predation in a savanna ecosystem

“…We examined the effect of prey neighborhood structure alongside the effects of two commonly considered “components” of predation (Lima and Dill , Moll et al. ), predator–prey encounter rates and catchability (the probability of a kill given an encounter, sensu Hopcraft et al. , Ford et al.…”

Habitat complexity mediates the predator–prey space race

“…This inherent complexity makes it difficult to disentangle behavioral motivations and choices of focal predator and prey species, and has led to persistent questions about how predators affect prey space use and the predictability, generality, and strength of the ensuing antipredator responses in large herbivores (Moll et al. ). Much of the existing research has focused on prey behavioral responses in wolf‐prey systems of North America (Basille et al.…”

“…Recent studies have called for greater taxonomic and geographic diversity in this research area to test the generality and context‐dependency of prey responses to risk (Moll et al. ).…”