Predator and prey functional traits: understanding the adaptive machinery driving predator-prey interactions

Abstract

Predator-prey relationships are a central component of community dynamics. Classic approaches have tried to understand and predict these relationships in terms of consumptive interactions between predator and prey species, but characterizing the interaction this way is insufficient to predict the complexity and context dependency inherent in predator-prey relationships. Recent approaches have begun to explore predator-prey relationships in terms of an evolutionary-ecological game in which predator and prey adapt to each other through reciprocal interactions involving context-dependent expression of functional traits that influence their biomechanics. Functional traits are defined as any morphological, behavioral, or physiological trait of an organism associated with a biotic interaction. Such traits include predator and prey body size, predator and prey personality, predator hunting mode, prey mobility, prey anti-predator behavior, and prey physiological stress. Here, I discuss recent advances in this functional trait approach. Evidence shows that the nature and strength of many interactions are dependent upon the relative magnitude of predator and prey functional traits. Moreover, trait responses can be triggered by non-consumptive predator-prey interactions elicited by responses of prey to risk of predation. These interactions in turn can have dynamic feedbacks that can change the context of the predator-prey interaction, causing predator and prey to adapt their traits-through phenotypically plastic or rapid evolutionary responses-and the nature of their interaction. Research shows that examining predator-prey interactions through the lens of an adaptive evolutionary-ecological game offers a foundation to explain variety in the nature and strength of predator-prey interactions observed in different ecological contexts.

Keywords: Adaptations; Ecology; Evolution; Functional Traits; Predator; Prey.

Figure 1.. Depiction of classic and modern views of a predator–prey interaction.

A predator–prey interaction is represented as a module where consumptive effects are depicted by solid arrows and non-consumptive effects by dashed arrows. ( a) In the classic, generic view, predators have a negative consumptive effect on prey, and prey provide a positive nutritional benefit to predators. ( b– d) A modern view considers greater complexity due to interplay between predator and prey functional (physiological, morphological, and behavioral) traits. The predator–prey interaction is then decomposed into consumptive and non-consumptive effects. ( b) The success of the predator consumptive effect on prey is contingent on the alignment (double-headed arrows) between predator morphology (for example, gape width) and prey morphology (body size) and between predator behavior (for example, hunting mode) and prey behavior (for example, escape mode). The consumption of prey feeds directly to support predator physiological needs (the nutrient balance among maintenance, growth, and reproduction). The specific example here shows that physiology then directly determines predator morphology (for example, increased size) and behavior (for example, increased aggression), although behavior could also reciprocally determine physiology and morphology. ( c) A non-consumptive effect could arise when a predator has a negative effect on prey by eliciting a physiological stress response. Stress in turn alters prey physiology (for example, heightened metabolism), behavior (for example, alertness and vigilance), and morphology (for example, induction of escape morphology). ( d) The combination of consumptive and non-consumptive interactions leads to a total predator–prey interaction that becomes an adaptive game involving changes and feedbacks between predator and prey traits. The interactions are depicted in terms of predator and prey traits of a certain magnitude (size of circles). The nature of the game, however, can vary depending on the state of predator and prey (inset) in relation to each other, as determined by the magnitude of each other’s functional traits (size of the circles). Thus, the strengths of effects may depend on how the magnitude of physiological (for example, good condition [larger] or poor condition [smaller]), morphological (for example, large bodied [larger] or small bodied [smaller]), and behavioral (for example, bold [larger] or shy [smaller]) traits of predators and prey play off against each other in the adaptive, state-dependent game.