Using landscape analysis to measure pollinator requirements

Background/Question/Methods In North America, bumblebees (Bombus) are native and honeybees (Apis) are introduced.  Since their introduction to the United States over 250 years ago, honeybees have become important pollinators of many plant species.  The recent decline in native pollinator species diversity could be due, in part, to habitat degradation and/or fragmentation, as well as competition with non-native honeybees.  We studied the relationship between habitat fragmentation and bumblebee abundance in Vermont.  We studied bees at the flowers they visited in meadows and old-fields of varying sizes and degrees of isolation from both other meadows and from forests.  Agricultural fields (corn, alfalfa, and pasture) and urbanization adds to the fragmented landscape that these pollinators navigate.  Using GIS, we examined the effects of different land-use cover on bumblebee abundance.
Results/Conclusions The proportion of visits to flowers by bumblebees was positively correlated with percent forest cover and negatively correlated with percent pasture cover. In addition, bumblebee abundance increased with increasing distance to honeybee colonies and with the proportion of the plant species in the fields that are native.  These results suggest that bumblebee abundance is affected by many factors: density of honeybees (competition), floral composition in fields (floral morphology), and forest cover (nesting habitat).