Floral resources, body size, and surrounding landscape influence bee community assemblages in oak‐savannah fragments

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Fragmentation of natural habitats due to urban development is predicted to have negative impacts on species diversity. The surrounding landscape (or ‘matrix’) of urban or semi‐natural habitats can sometimes support biodiversity, but the amount of support will depend on species‐specific traits, and on the resources available in the fragment and the matrix. Using data on bees collected from 19 oak‐savannah fragments, the question of whether bee communities differ when fragments are embedded in different landscapes (Douglas‐fir forest vs. urban residential neighbourhoods) was investigated, and also whether these differences could be attributed to species‐specific traits of bees (e.g. body size, specialization) and/or within‐fragment floral resources. No differences were found in overall richness or abundance of bees, but there were distinct differences in plant and bee community composition between matrix types. Common wood‐nesters and late‐flying, small‐bodied bees tended to be found in urban‐associated fragments, which also had a lower availability of within‐fragment floral resources. Forest‐associated fragments, on the other hand, had a greater density and richness of early‐flowering native plant species, and supported a higher abundance of large‐bodied bee species. Bumble bee abundance, in particular, increased with increasing proportion of forest cover in the surrounding landscape. Large‐bodied bees appear to respond to increased availability of within‐fragment floral resources, but it was also hypothesised that nesting and floral resources in matrix habitat drive the differences in bee community assemblages.