The effects of forest fragmentation on bee communities in tropical countryside.
Despite ongoing concerns and controversy over a putative 'global pollination crisis' there is little information on the response of bees, the most important group of pollinators, to land-use change. In particular, there are no published studies of the effects of tropical forest fragmentation on entire bee communities. We examined bee community responses to forest fragment size, shape, isolation and landscape context (forest variables) by sampling foraging bees at ground level using aerial netting within, and in pastures adjacent to, 22 forest fragments ranging in area from c. 0.25 ha to 230 ha, in southern Costa Rica. We sampled each site 13 times in total, in both wet and dry seasons. Although there were no effects of forest variables on bee diversity and abundance, we did find strong changes in bee community composition. In particular, tree-nesting meliponines (social stingless bees) were associated with larger fragments, smaller edge:area ratios and greater proportions of forest surrounding sample points, while introduced Apis showed opposite patterns. Community composition was also strikingly different between forests and pastures, despite their spatial proximity. In forests, even in the smallest patches, meliponines comprised a much larger proportion of the apifauna, and orchid bees (euglossines) were common. In pastures, Apis was much more abundant and no euglossine bees were found. These results agree broadly with other studies that have found contrasting responses to habitat fragmentation from different bee groups. Conserving meliponine bees, important for pollination of coffee and other crops, and euglossine bees, critical in long-distance pollen transport, will require forest. Synthesis and applications. In the first study of the effects of tropical forest fragmentation on entire understorey bee assemblages, we found bee community resilience to land-use change, as deforested sites and small forest fragments can have a diverse component of bees. While bees as a whole show some degree of resilience to land-use change, there are taxon-specific responses and, in our study area, there is clear value to conserving native forest, particularly for the ecologically and economically important meliponine and euglossine bees.