Toward a predictive theory of risk effects: hypotheses for prey attributes and compensatory mortality

Abstract

Abstract. Risk effects, or the costs of antipredator behavior, can comprise a large proportion of the total effect of predators on their prey. While empirical studies are accumulating to demonstrate the importance of risk effects, there is no general theory that predicts the relative importance of risk effects and direct predation. Working toward this general theory, it has been shown that functional traits of predators (e.g., hunting modes) help to predict the importance of risk effects for ecosystem function. Here, I note that attributes of the predator, the prey, and the environment are all important in determining the strength of antipredator responses, and I develop hypotheses for the ways that prey functional traits might influence the magnitude of risk effects. In particular, I consider the following attributes of prey: group size and dilution of direct predation risk, the degree of foraging specialization, body mass, and the degree to which direct predation is additive vs. compensatory. Strong tests of these hypotheses will require continued development of methods to identify and quantify the fitness costs of antipredator responses in wild populations.

Limited spatial response to direct predation risk by African herbivores following predator reintroduction

“…Direct mortality can lead to declines in prey populations (Eberhardt et al. 2007) and is the most commonly measured consequence of predation (Creel and Christianson 2008; Creel 2011). However, a growing number of studies have demonstrated that risk effects can be as strong as, or even stronger, than consumptive effects (Preisser et al.…”

“…2014). This has limited our understanding of risk effects and our ability to predict their consequences and costs across different prey species and ecosystems, with little known about how characteristics of predators, prey, and/or the environment influence responses (Creel 2011). …”

“…2014). However, differences in prey traits are expected to mediate antipredator responses even more than predator hunting mode because prey characteristics affect all aspects of prey response to risk, compared with predator traits that affect only some responses (Creel 2011). Although little is known about the factors driving variation in antipredator responses within and between prey species, foraging strategy and body size have been shown to mediate response strength.…”

Predicting population‐level risk effects of predation from the responses of individuals

“…Such predator risk effects can lead to significant changes in population dynamics, with effects cascading through communities and across different trophic levels in both terrestrial and marine ecosystems (Schmitz 2003, Schmitz et al 2004, Creel et al 2005, 2007, Baum et al 2007). The key role of risk effects in ecological systems has generated considerable interest in trying to predict their effects from general principles, with habitat effects, predator hunting mode, and prey characteristics all being shown to provide some ability to predict impacts (Trussell et al 2006, Schmitz 2008, Creel 2011, Matassa and Trussell 2011. However, there is, as yet, no general theoretical framework in population ecology for predicting when and how such risk effects will arise or how strong they will be (Creel andChristianson 2008, Creel 2011).…”

Top Down Control in a Relatively Pristine Seagrass Ecosystem

“…For example, in an old-field system with herbaceous plants, grasshopper herbivores, and spider predators, grasshoppers experienced significantly higher mortality in experiments with spiders that had their chelicerae glued (risk spiders) and in unglued (predatory spiders) trials when compared to a no-spider control (Schmitz et al 1997). In some situations, risk effects may rival or even exceed the influence of direct predation on prey populations and communities (Werner and Peacor 2003, Preisser et al 2005, Creel and Christianson 2008, Creel 2011. As an example, Schmitz et al (1997) (Ripple and Beschta 2004, Creel et al 2005, Hernández and Laundré 2005, Fortin et al 2005.…”