Are Tolerance, Avoidance, and Antibiosis Evolutionarily and Ecologically Equivalent Responses of Plants to Herbivores?

Plants possess numerous traits that reduce the potentially detrimental effect of herbivores. These traits, referred to as “defense traits,” fall into two broad categories, resistance traits, which reduce herbivory, and tolerance traits, which reduce the impact of herbivory on fitness. Plant resistance can be further divided into avoidance, which affects herbivore behavior (i.e., recognition or preference for a particular plant), and antibiosis, which reduces herbivore performance (Painter 1958; Futuyma 1983). Examples of avoidance traits include egg mimics in Passiflora sp. that reduce oviposition by Heliconius (Williams and Gilbert 1981) and may also include feeding inhibitors or, conversely, reduced concentrations of feeding or oviposition stimulants (Fraenkel 1959; Jermy 1966; Feeny et al. 1983). Examples of antibiotic resistance traits are numerous and include alkaloids, cardenolides, cyanogens, fouranocumarins, and glucosinolates (reviewed in Rosenthal and Berenbaum 1991; Bernays and Chapman 1994). Lack of evidence for correlations between host preference and herbivore performance suggest that these two resistance strategies often may be independent (Thompson 1988; Thompson et al. 1990; Pilson 1992; but see Via 1986). The distinction between preference and performance, although incorporated into models of the evolution of herbivorous insects (Georghiou 1972; Gould 1984; Lockwood et al.