A framework and standardized terminology to facilitate the study of predation‐risk effects

Abstract

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

Broadening the ecology of fear: non-lethal effects arise from diverse responses to predation and parasitism

“…Trait responses to either predators or parasites can have trade-offs that trigger non-lethal effects, including reduced individual fitness and 'trait-mediated indirect effects' [13], like trophic cascades [14][15][16] that shape communities [17]. Wolves, for example, frighten elk away from open foraging grounds into sheltered habitats with less nutritious vegetation, which then reduces elk birth rates [18] and alters vegetation structure [19].…”

Environmental gradients influence biogeographic patterns of nonconsumptive predator effects on oysters

“…While these anti‐predator responses can reduce the probability of being consumed, they are often associated with fitness costs to the prey through reduced growth and reproduction as well as increased mortality (non‐predation‐related); these costs have been labeled nonconsumptive effects (NCE) of predators (Peckarsky et al 2008). Because the NCEs and consumptive effects (CEs) of predators can lead to different outcomes for prey, their resources, and ecosystem functioning (Schmitz 2008), the frequency of research devoted to detecting NCEs and identifying when, where, and why they are important continues to grow (Preisser et al 2005, Peacor et al 2020).…”

Bugs scaring bugs: enemy‐risk effects in biological control systems

“…have weak consumptive effects, CEs) but instead have large impacts on prey fitness and prey interactions with the rest of their community (Preisser et al ., 2005). These three levels of effect (individual response, impacts on fitness/populations and community effects) are best defined as enemy‐induced trait responses , non‐consumptive effects and trait‐mediated indirect effects (Peacor et al ., 2020). Box 2 discusses this terminology in greater detail.…”