Urbanization and anthropogenic development across North America are contributing to habitat loss and fragmentation. Urbanization also alters surface water systems, resulting in the elimination, alteration, and creation of aquatic ecosystems. Habitat loss is one factor contributing to the current native bee and honeybee (Apis mellifera) population declines across the continent. Previous studies on the effect of urbanization on bee populations have produced conflicting results, which suggest that further research is required. The effect of surface water availability on bee populations is not well studied. Using bee bowl traps and sweep net sampling techniques in household yards across the Twin Cities in Minnesota, I assessed bee abundance and bee community composition across an urban to rural gradient using housing density as a measure of degree of urbanization. I also examined and compared bee communities in yard sites both near to and far from major surface waters. Specifically, I tested the hypothesis that bee community assemblages are affected by both housing density and proximity to water, independently. I found no significant difference in bee abundance across the urban to rural gradient or at varying distances from water. However, I found a positive correlation between yard size and bee abundance and a significantly different community composition of bees near to and far from water. The results of this study imply that bee populations are not affected by housing density alone, and that other factors, such as habitat patch size as measured by yard size, may be contributing to reported declines in bee populations. Results also imply that altering surface waters in urban areas can impact bee community composition. These results can help guide future studies and inform urban planning and surface water alteration methods in order to conserve bee populations.
Dynamic specialization refers to the concept that animals do not have fixed niches, but that, instead, niches are malleable and dependent on the community composition of sympatric and competing species. My study examined dynamic specialization in a bee community near Flagstaff, Arizona, by assessing temporal and spatial changes in floral constancy, which might be driven by niche partitioning, resource availability and diet breadth. I found that bees do exhibit temporal and spatial dynamic specialization and that some bee species are more likely to collect randomly from local resources than other species. This bee community preferred certain species of flowers, notably in the Rosaceae, and disfavored others, such as those in the Fabaceae. All bee species caught were broadly polylectic, and this generalist community did not show niche partitioning. These findings have implications for the conservation of native bees in the U.S. southwest as they face threats from climate change, encroachment from non-native species and anthropogenic forest management.
