Background/Question/Methods  In Chicago, like most urban landscapes, areas of native habitat are often small, isolated and located within vast expanses of development, such as suburbs or urban centers (Panzer & Schwartz, 1998; Robertson & Schwartz, 1994).  In some cases, remnant fragments of native habitat may be augmented by open land or anthropogenically altered landscapes able to function as suitable habitat. 
The entire home range of insects living in fragmented landscapes may comprise of several partial habitats, each providing a different resource such as nesting sites, mating, and foraging sites. Partial habitats are often divided by areas not suitable to bees, however naturally patchy distributions are the norm for native wildflowers (Cane, 2001). Size, number and distance between partitioned fragments, along with the type of partitioning combined determine the ability of each fragment to function independently or as a portion of a matrix.
We investigated the relation between urban habitat and pollinator activity within the native bee community. For this project we had two goals, to determine the bee diversity at sites with different degrees of urbanization, and measure pollination activity at these sites. The first was achieved using aerial nets and pan traps to capture a sample of insect species in the area. Bees caught were identified to genus, and species when possible. In addition we surveyed the pollinator services by bees directly through pollinator observations at Penstemon sp. and Rudbeckia sp. for two summers in and around Chicago. Our 30 sites included restored prairies, Chicago city parks, and green roofs in downtown Chicago ranging from two to over 70 stories tall.
Results/Conclusions  

In an overall comparison of urban to prairie sites the composition of the bee communities among sites were very different, however, there were not significantly different numbers of total visits per site.  There were significantly fewer ground nesting bees in urban sites versus restored prairies, a common result in urban bee studies. We also found greater numbers of non-native bees in urban sites compared to restored prairies. Overall, our results indicate urban parks are able to provide suitable habitat for many types of native bees, and therefore implicate the potential for urban rooftops to do the same.