Relationship of bee community composition to floral and nesting resources, habitat structure, land use, and fire history along an open-forest gradient

Background/Question/Methods

Concern over possible global pollinator declines has increased the need to understand the ecology of native bees.  Across twenty-five sites at Indiana Dunes National Lakeshore and surrounding natural areas in northwest Indiana, we examined how plant diversity, availability of nesting resources, woody vegetation density, patterns of human use of landscapes, and fire history were related to the abundance of bees and the composition of bee communities.

Results/Conclusions

Neither bee abundance nor richness or composition of bee communities within sites was significantly related to proximity of sites to each other.  Nestedness analysis indicated that species composition in less species rich sites was not merely a subset of species composition at richer sites.  The lack of significant proximity or nestedness effects is consistent with bees’ use of sites being shaped by factors at a small scale.  Different sets of variables best predicted bee abundance, richness, and composition across the twenty-five sites.  Bee abundance was significantly related to habitat structure and fire history, bee richness to floral richness, and bee community composition to floral richness and nesting resources.  Human uses of the landscape surrounding sites, such as for agriculture and housing, did not significantly predict abundance or richness of bee assemblages.  The results suggest that patterns of floral diversity, nesting resources, and habitat shading, present at the scale of a few hundred meters, are key determinants of bee community patterns in the mosaic grassland-savanna-forest landscape of the Indiana Dunes region of northwest Indiana.