Urbanization is an important anthropogenic force with significant consequence for the abundance and diversity of biotic communities. Traits at both local- and landscape-scales play a role in determining the patterns of flora and fauna in cities. One taxon of particular concern is insects, which provide invaluable ecosystem services and can serve as indicators of more general biodiversity trends, but are declining at an alarming rate. Because distinct landscape patterns can differ in their consequences for insects, it is important to study population trends across various geographic contexts. Here we study how the abundance of flying insects orders in urban gardens changes along an urban-to rural gradient around the “shrinking city” of Detroit, MI, evaluating the effect impervious land cover and floral composition, as well as potential trade-offs between taxonomically distinct pollinator groups. In the summer of 2014 insects were sampled every two weeks using colored pan traps and bottle traps. Floral surveys were conducted to assess local-scale vegetation quality, and Geographic Information Systems (GIS) was used to assess landscape-scale urban intensity measurements around sampling sites.
Results/Conclusions
Preliminary results show that increasing urban intensity was found to negatively impact insect abundance across taxonomic groups, although the extent of this impact varied for particular orders and depended on the spatial scale at which urban intensity was measured. This is potentially attributable to divergent life history traits across insect taxa. Surprisingly few floral variables had a measurable impact on insect abundance, even for important pollinators that depend on floral resources like nectar and pollen. Both insect abundance and impervious surface were also correlated with the area of “weed”/non-crop flowers in garden plots, suggesting potential synergies between local- and landscape- drivers of urban insect population trends. Finally, we found no trade-off between bee and hoverfly pollinators across urban garden sites. Overall these results point to significant local- and landscape-scale drivers of changes in insect communities in and around cities, and they suggest new research directions and conservation strategies in urban agroecosystems.