Effects of Predator Avoidance Behavior on the Coexistence of Competing Prey

Abstract

Predator avoidance behavior, in which prey limit foraging activities in the presence of predation threats, affects the dynamics of many ecological communities. Despite the growing theoretical appreciation of the role predation plays in coexistence, predator avoidance behavior has yet to be incorporated into the theory in a general way. We introduce adaptive avoidance behavior to a consumerresource model with three trophic levels to ask whether the ability of prey-the middle trophic level-to avoid predators alters their ability to coexist. We determine the characteristics of cases in which predator avoidance behavior changes prey coexistence or the order of competitive dominance. The mechanism underlying such changes is the weakening of apparent competition relative to resource competition in determining niche overlap, even with resource intake costs. Avoidance behavior thus generally promotes coexistence if prey partition resources but not predators, whereas it undermines coexistence if prey partition predators but not resources. For any given case, the changes in the average fitness difference between two species resulting from avoidance behavior interact with changes in niche overlap to determine coexistence. These results connect the substantial body of theoretical work on avoidance behavior and population dynamics with the body of theory on competitive coexistence.

Quantifying the relative importance of competition, predation, and environmental variation for species coexistence

“…Connections between the theories are becoming more common (e.g. Kuang & Chesson (2008); Sommers & Chesson (2019)), including recent developments that incorporate niche and fitness differences (Godoy et al , 2018). A unified framework that incorporates direct competition between species together with effects of predation is necessary for gaining a synthetic understanding of how biodiversity is maintained.…”

“…While here we focus on how the underlying structure of food webs and species’ demography may promote coexistence, a similar approach could additionally incorporate behavioral dynamics. For example, recent work by Sommers and Chesson (2019) show that predator avoidance behavior by prey species can alter coexistence via changes in the importance of apparent competition relative to resource competition. If prey species partition resources, these behavioral changes tend to promote coexistence; when prey species instead partition predators, behavioral modifications undermine coexistence (Sommers & Chesson, 2019).…”

“…For example, recent work by Sommers and Chesson (2019) show that predator avoidance behavior by prey species can alter coexistence via changes in the importance of apparent competition relative to resource competition. If prey species partition resources, these behavioral changes tend to promote coexistence; when prey species instead partition predators, behavioral modifications undermine coexistence (Sommers & Chesson, 2019). In multiple empirical systems, behavioral changes in prey species via fear-driven avoidance are similarly well documented, such as with brown anoles, green anoles, and curly-tailed lizards on tropical islands (Pringle et al , 2019).…”

Predators affect competitors’ coexistence through fear effects

“…This explanation is intuitively satisfactory. But it leaves out a potentially important piece of the story, which has long been addressed by theory [5][6][7][8] : that predators might determine which species coexist, by mediating competitive interactions.…”

“…The mere perception of a predation risk can cause prey to adaptively change their behaviour, morphology or physiology to alleviate the pressure of predation 9 . In particular, prey can take refuge in predator-free habitats 9,10 , which could intensify the competition between species for particular territories and resources 8 . Known as refuge competition, this effect then disrupts coexistence, reducing diversity ( Fig.…”