The Effect of Environmental Disturbance on a Tropical Butterfly Population

Abstract

Near Turrialba, Costa Rica, the only common host plant of the black swallowtail butterfly Papilio polyxenes Fabr., Spananthe paniculata, is an early successional umbellifer that occurs in ephemeral patches that vary in age, size, and degree of isolation from one another, and support localized colonies of P. polyxenes. Within one patch, egg and larval survival was highest shortly after the plants began to flower. Eggs experimentally placed on the leaves of plants prior to flowering suffered rates of mortality nearly twice as great as those placed on flowers just 2 or 3 wk later. Beyond the point egg and larval survival decreased as rates of predation increased, local population densities increased, or infertility occurred. During this period, the numbers and kinds of insects from predominantly predaceous and parasitic families increased significantly, as did the numbers of spiders. The overall importance of three measured sources of mortality were: predation by large predators > predation by small predators > drowning due to rain. Year—round breeding and dispersal by black swallowtail adults allows them to colonize new patches as they appear and to track the spatial availability of the ephemeral host in time. New patches provide a continual supply of temporary refuges from natural enemies and areas of high intraspecific population density. The black swallowtail is only one of a variety of anthropods that appears to be adapted for colonizing asynchronous habitat patches produced by localized disturbances where the growing season is continuous.