PLANT APPARENCY AND EVOLUTIONARY ESCAPE FROM INSECT HERBIVORY

Temporal variation in host availability between years may be the dominant parameter determining host associations in a large assemblage of pierid butterflies (Lepidoptera: Pieridae) feeding on plants (Capparales) living in a seasonal environment (Morocco). Stenophagous butterflies are associated with hosts whose densities are predictable from year to year. In contrast, euryophagous consumers use both predictable and highly variable hosts that often occur at low densities. There is little evidence for altered host-use patterns when consumer species co-occur. Herbivore diet breadth and specificity are unrelated to consumer community composition and are better understood in terms of factors determining adaptation to habitats and potential hosts. Two groups of potential hosts escape herbivory: apparent, predictable species whose chemistry is probably atypical of Capparales and species with low apparency and low predictability. These latter species are also generally unpalatable and unsuitable for larval growth, a finding that contradicts the widely held view that less apparent plants are more palatable than apparent plants. We propose that the inverse relation between apparency and palatability observed in temperate-zone studies is an intermediate stage in an evolutionary trajectory leading to permanent escape from herbivory as herbivores lose adaptation to seldom encountered hosts. Potential hosts may therefore escape herbivory by two evolutionary trajectories: (1) acquisition of novel chemistry (or other trait) that is too different to be accomodated by existing variation in the consumer population (an escalation of the "arms race") and (2) reduction in apparency and predictability, or "ecological escape," followed by gradual accumulation of changes that herbivores are unable to track.