Associate Professor Utah State University, Utah, United States
Abstract: Inducible defenses are a type of plastic response common in microbes, invertebrates and vertebrates; they involve changes in individual behavior, life history, or morphology that reduce exploitation by predators or natural enemies. Inducible defenses can be reversible or irreversible, have equal or unequal rates of induction and loss of induction, and be stimulated by predator cues, conspecific cues, cues from conspecific predation, or a comprehensive set of cues that allows prey to accurately assess fitness (i.e., the fitness gradient). The goal of this study is to explore how differences in these characteristics influence the ways in which inducible defenses alter predator-prey dynamics. We did this by analyzing the stability and phase-lags of predator-prey oscillations in a predator-prey model with an inducible prey defense. We find that inducible defenses are typically stabilizing, but defenses driven by any cue can be destabilizing when individual prey fitness is strongly affected by the population mean defense level. Slower rates of loss of induction increase the stabilizing effects and reduce the destabilizing effects, with irreversible defenses being the most stabilizing and least destabilizing. Induced defenses typically drive predator-prey cycles with lags less than a quarter-period, but inducible defenses driven by conspecific density or the fitness gradient can cause lags up to a half-period. This study extends and unifies our understanding of how differences between induced defenses scale up to influence the population-level dynamics of predator-prey systems.
