Patch and landscape factors shape community assemblage of bumble bees, Bombus spp. (Hymenoptera: Apidae), in montane meadows

Abstract

Understanding the scale at which habitat influences species richness in terrestrial ecosystems is central to both ecology and conservation biology [Wettstein, W., Schmid, B., 1999. Conservation of arthropod diversity in montane wetlands: effect of altitude, habitat quality and habitat fragmentation on butterflies and grasshoppers. Journal of Applied Ecology, 36, 363–373]. Community composition may be influenced by habitat variation at patch and/or landscape-scales depending on the body size, home range area, and dispersal distances of the focal taxa [Calder III, W.A., 1984. Size, function, and life history. Harvard University Press, Cambridge, MA; Haskell, J.P., Ritchie, M.E., Olff, H., 2002. Fractal geometry predicts varying body size scaling relationships for mammal and bird home ranges. Nature 418, 527–530; Thomas, C.D., 2000. Dispersal and extinction in fragmented landscapes. Proceedings of the Royal Society Biological Sciences Series B 267, 139–145], not merely their phylogenetic affinity. We investigated the importance of habitat variables at different scales on the richness and abundance of bumble bees both annually and seasonally in Sierran montane meadows over two years. We found that both patch and landscape factors influence the species richness and abundance of bumble bees and these factors have a seasonal component to their importance. The proportion of meadow in the surrounding habitat was the most consistent positive influence on both species richness and abundance across years. In the second year, 2003, patch factors, plant species richness and current livestock grazing also influenced bumblebee species richness; plant species richness was positively correlated and current livestock grazing was negatively correlated with bumble bee species richness. Bumble bee abundance was positively influenced by meadow wetness and proportion of meadow in the surrounding habitat in both years. These data suggest conservation of pollinators depends on conservation planning with attention to the quality and context of the landscape.