Life History Modulates Effects of Inducible Defenses on Consumer-Resource Dynamics

AbstractInducible defenses can affect the persistence, structure, and stability of consumer-resource systems. Theory shows that these effects depend on characteristics of the inducible defense, including timing, costs, efficacy, and sensitivity to consumer density. However, the expression and costs of inducible defenses often vary among life stages, which has not been captured in previous unstructured models. To explore how inducible defenses expressed in stage-structured populations affect consumer-resource dynamics, we developed a model based on the biology of plant-herbivore interactions, with the plant (resource) population structured into juvenile and mature stages. We then investigated the joint effects of inducible defenses and resource life history (i.e., patterns of fecundity, maturation, and mortality) by simulating dynamics for plant populations occurring along a fast-slow pace-of-life continuum. In general, high inducible defense costs, or a slow pace of life coupled with high herbivore growth rates, promoted persistent cycles. However, these cycles fundamentally differed, with either the plant or the herbivore population peaking first. Additionally, plant population pace of life influenced the relative effects of stage-specific induction strength on equilibrium densities and the extent to which inducible defenses enabled persistence. Our work illustrates how life history modifies the population-level effects of trait-mediated interactions, with implications for conservation and pest management.