Why Induced Defenses May Be Favored Over Constitutive Strategies in Plants

Abstract

Although induced resistance has been documented in over 100 species of plants, why plants employ facultative defense strategies is not well understood. Although it has been widely accepted that induction may be a means of reducing resource allocations to defense when not needed, this explanation is not exclusive of a wide array of hypotheses for the advantages of induced defenses. In an attempt to shift attention away from the “allocation cost” model, here we focus on several alternative hypotheses for the benefits of induction. Given that most plants interact with multiple specialist and generalist herbivores, various pathogens, microbes, and mutualists, a host of constraints on maintaining constantly high levels of resistance arise. The temporal and spatial variability in food quality for phytophages created by induction may be especially important. Variability may hinder herbivore performance in ecological time as well as the evolutionary ability of herbivores to adapt to host plants. Research on the various benefits of induced defenses seems to be the obvious next step in understanding why so many plants employ induction.

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