Wednesday, August 18, 2010

Wrapping things up, ctd: the bees' needs (and other results)

In total, 50 bee species were found by CAPS citizen scientists. An additional 16 species (66 total) were found in Chicago Park District community gardens, and when we add the specimens collected last summer in Cook County Forest Preserves by undergraduates at Roosevelt University, that number jumps to 79 species found in the Chicago region. The expert who identified the specimens noted that a number of the species are uncommon or even rare in this part of the county, and, though this still needs to be confirmed, it appears that a few may even be the first record in the State of Illinois!

A major goal of the study was to gather data from a wide geographical area (in this case, the Chicagoland area) to examine whether the pollinator communities differed across the region; in other words, we wanted to see if the community of bees in South Shore was similar to or different from the community of bees in Lake Bluff. We also paid attention to the differences between collection sites - between your small backyard in Rogers Park, a vegetable-filled community garden in Jackson Park, and a wooded forest preserve in Des Plaines.

While there were some obvious differences between the site types - for example, community gardens generally had more species that backyards - we were also interested in how the areas surrounding the sampling locations may influence these differences. To do this, we looked at the population density (the number of people living in a given area), amount of impervious surface (paved parking lots versus prairie), and amount of tree cover (thick woods versus open skies) in the vicinity of each site. These characteristics were chosen because of the effects they may have on the resources necessary for the pollinators, such as their requirements for nesting (the place where these little guys hand their hats and reproduce) and foraging (where they go out searching for grub).

In general, a few patterns emerged. First, the number of species (species richness) found at each site was influenced by the percentage of impervious surface in the surrounding area, with less impervious surface resulting in higher species richness. Second, the amount of tree canopy in the surrounding area had an opposite effect, with a higher percentage of tree cover resulting in a lower species richness. While somewhat counterintuitive - plants are good, right?! - this makes sense because most trees do not provide the resources (namely, pollen and nectar) that pollinators like bees depend on. Third, increased population density was shown to have a slightly positive effect on the number of species at each site, meaning that the more people living in an area, the higher the number of bee species. While we need to look into this trend further, we wonder if this might be a result of the likelihood of people planting flowers for bees to forage on.

One notable species that was found in the collections in Peponapis pruinosa, a medium-sized bee that is known to specialize on squash blooms (hence its common name, the squash bee). Of the 33 backyard sites in the study, one one squash bee was reported from a yard in Deerfield, IL. However, the squash bee was found in 4 of 11 community gardens, showing that bees do adhere to the "if you plant it, they will come" mantra.

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