Persistence of a frugivorous butterfly species in Venezuelan forest fragments: the role of movement and habitat quality

We studied the factors affecting the persistence of a frugivorous butterfly species, Hamadryas februa, in a set of forested islands located in Lago Gu ri, a reservoir in eastern Venezuela. The roles of isolation, area and habi tat quality (larval host plant density, light conditions and presence of fr uiting trees) in determining island butterfly densities were investigated t hrough observations and experiments. Butterfly densities increased signific antly with increase in both island area and local larval host plant density , but were not related to distance from colonizing sources, light condition s or presence of fruiting trees. Butterfly populations on even distant isla nds were not augmented by the experimental introduction of adults. Butterfl y residence times were higher on sites located on a large island than on sm all islands. However, there was no evidence that the positive correlation b etween adult density and host plant density was caused by increased reprodu ction. The results indicate that butterfly densities are not constrained by colonization capabilities but rather, by lack of appropriate host plants a nd high rates of emigration from islands. The study indicates the importanc e of considering patterns in movement and habitat heterogeneity when design ing conservation strategies for insects in fragmented landscapes.