Herbivory in a fragmented tropical forest: Patterns from islands at Lago Gatún, Panama

Abstract

By imposing density-dependent mortality upon their hosts, specialistinsect herbivores are thought to contribute to the maintenance of tree diversityin tropical forests. Forest fragmentation may alter patterns of herbivory,however, which may have important implications for tree species diversity inforest remnants. To explore effects of fragmentation on patterns of herbivory,we assessed folivory by Lepidopteran larvae on saplings of four focal treespecies on eight artificial, forested islands at Lago Gatun, Panama. Weexplored the importance of island area, distance to larger land, exposure to dryseason winds, tree species, and season in determining proportions of new leavesdamaged by caterpillars, and proportions of leaf area lost to caterpillars,during two dry and wet seasons. We found that both measures of herbivoryincreased markedly with island area, that island isolation had no apparenteffect on herbivory, and that interactions between season and exposure, andbetween tree species and season, were important determinants of herbivory rates.In addition, we observed species-specific differences in herbivory among hostplants under various conditions imposed by fragmentation. We conclude thatpatterns of herbivory by Lepidopteran larvae are sensitive to fragmentation inthis tropical forest. Differential herbivory among the four tree speciesconsidered here may have important implications for tree species dynamics on theislands of Lago Gatun.