Frugivorous butterflies in Venezuelan forest fragments: abundance, diversity and the effects of isolation

Frugivorous butterflies were studied in a set of forested islands (0.1 to 1 .15 ha) in a reservoir in eastern Venezuela to investigate the effects of f ragmentation and the resulting isolation on their abundance, diversity and species composition. While some islands showed reduced abundance and specie s diversity in comparison to unfragmented (or control) sites, others did no t. Isolation status affected both butterfly abundance and diversity. Island s located close to their colonizing sources (0.1-1 km) tended to support si milar densities of butterflies but lower numbers of species in comparison t o control sites. Far fragments (1-3 km from their colonizing sources) tende d to harbour lower butterfly densities in comparison to control sites but u ndiminished numbers of species. Species composition varied significantly be tween control sites and islands and amongst control sites, near islands and far islands. Interspecific differences were observed in species' responses to fragmentation. Charaxines, medium-sized satyrines, morphines and brasso lines may be vulnerable to extinction after habitat fragmentation while sma ll-sized satyrines may be relatively resistant. Observations during the dry season indicate that butterfly species may exist as mainland-island metapo pulations in Lago Curl, in which small habitat fragments require recoloniza tion every year from source populations in large islands and mainland habit at.