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

By imposing density-dependent mortality upon their hosts, specialist insect herbivores are thought to contribute to the maintenance of tree diversity in tropical forests. Forest fragmentation may alter patterns of herbivory, however, which may have important implications for tree species diversity in forest remnants. To explore effects of fragmentation on patterns of herbivory, we assessed folivory by Lepidopteran larvae on saplings of four focal tree species on eight artificial, forested islands at Lago Gatún, Panama. We explored the importance of island area, distance to larger land, exposure to dry season winds, tree species, and season in determining proportions of new leaves damaged by caterpillars, and proportions of leaf area lost to caterpillars, during two dry and wet seasons. We found that both measures of herbivory increased markedly with island area, that island isolation had no apparent effect on herbivory, and that interactions between season and exposure, and between tree species and season, were important determinants of herbivory rates. In addition, we observed species-specific differences in herbivory among host plants under various conditions imposed by fragmentation. We conclude that patterns of herbivory by Lepidopteran larvae are sensitive to fragmentation in this tropical forest. Differential herbivory among the four tree species considered here may have important implications for tree species dynamics on the islands of Lago Gatún.