Life History Trade-Offs Between Growth and Anti-Herbivore Defenses

Plants have evolved a battery of defenses that have proven effective at reducing loss of leaf tissue to herbivores. Yet, even though defenses reduce herbivory, species differ dramatically in their investment. In 1976, Feeny proposed apparency theory suggesting that species that were long-lived (“apparent”) would be easily found by both specialist and generalist herbivores and would invest in broadly effective defenses. In contrast, ephemeral species (“unapparent”) could escape discovery by specialists and would only need to invest in defenses effective against non-adapted generalists. Coley’s dissertation, which led to the resource availability hypothesis, was a test of this, measuring defenses and herbivory on saplings of 41 gap specialists (“unapparent”) and shade tolerant species (“apparent”). The results did not support apparency theory. Instead, the resource availability hypothesis posits that the inherent growth rates of species are adapted to the typical availability of resources in their preferred habitat and that slow growth selects for high investment in defense.