MARCH 2012

City size, regional landscape context, and local resource characteristics influence patterns of bee occurrence: A case study from northwestern Costa Rica

by Victoria A. Wojcik

Pollinator Partnership, 423 Washington Street, 5th floor, San Francisco, CA 94111

University of California, Berkeley Department of Environmental Science, Policy, & Management, 132 Mulford Hall, Berkeley, CA 94620

E: victoriawojcik@hotmail.com; vw@pollinator.org

T: 510-697-3890/415-362-1137

F: 415-362-3070

Abstract

Understanding the ecological patterns of bees in cities can aid in their conservation and management. This is especially important in regions experiencing rapid anthropogenic change that threatens the survival of these important pollinators and the ecological services that they provide. To study occurrence trends at the community level, bees visiting a common and abundant floral resource species, Tecoma stans, were sampled across three urban landscapes located in the tropical dry forest of northwestern Costa Rica. Frequency-of-visitation counts that measured both bee visitor abundance and bee taxon richness were used to assess foraging variation and individual resource constancy, and to evaluate the effects of plant resource characteristics (floral abundance, resource size, and vertical structure), city size, and regional landscape context on bee occurrence. Of the resource characteristics studied, only the total number of flowers at a food resource had a significant impact on bee occurrence, with resources that possessed more flowers attracting more bees and more bee types. The taxon richness observed at a resource increased significantly as city size increased, but there was no association between city size and bee visitor abundance. Cities located within similar regional landscapes had similar bee community composition, indicating that the surrounding landscape influenced species presence and absence patterns. The patterns of occurrence recorded in this study can be seen as a positive result for bee conservation and management in urban landscapes; the correlation of high bee visitation with abundant flowers suggests that efforts to increase resource availability should be successful in producing a corresponding increase in bee presence.

Keywords: bees, hymenoptera, pollinators, foraging, resource characteristics, regional landscape, tropical dry forest, Costa Rica, Tecoma stans