Why should we care about beetles and their response to the changing urban landscape?

            With increased urbanization comes increased disturbance of natural habitats for organisms around the globe. As skyscrapers, vast concrete surfaces, small green areas, and landscaped parks and gardens become more and more common, organisms have to find ways to survive in new and fragmented habitats. Many scientists have struggled with the difficult question of how urbanization will affect different and ecologically important species; however, it is difficult to generalize about the effects of urbanization. Therefore, it is important to understand this concept in a localized way since there are a variety of factors that come into play, including the scale of urbanization, the intensity, the geographic location, and the natural ecology of the area. Grinnell College’s campus, which is set in the middle of rural Iowa, is teeming with biodiversity. From butterflies to grasshoppers to vultures to native prairie plants, there is a lot to be studied. Grinnell College is a moderately urbanized area with lots of green space, landscaped gardens, as well as reconstructed prairie patches. Our research team was interested in understanding the local effects of urbanization on Grinnell’s campus.

            In Dr. Michael L. McKinney’s study, “Effects of urbanization on species richness: A review of plants and animals,” he dives into some complex questions about the effects of urbanization on species richness (or the number of different species) in different taxonomic groups (2008). In an attempt to answer these difficult questions, he reviews a total of 105 studies on plants, mammals, reptiles, amphibians, and invertebrates with low, moderate, and high levels of urbanization. While there is significant evidence in the literature for a consistent decrease in species richness with increased urbanization, there are some studies that show a surprising increase in species richness with intermediate levels of disturbance. In his review, McKinney interestingly found that the majority (65%) of the urbanization studies done on plants show an increase in species richness going from low to moderate levels of urbanization. However, this was not the case for vertebrates and invertebrates. Plants were the only taxa studied that showed a peak in species richness at moderate levels. All other taxa had species richness peaks in low urbanization settings. Additionally, there was no evidence for an increase in species richness going from moderate to high urbanization levels across all taxa. McKinney suggests here that human importation of non-native plants for landscaping purposes is the main reason for this trend in species richness this importation will outpace native species extinctions and lead to increased species richness at moderate levels of urbanization. This is not the case for other taxa; however, there are a lot of factors that affect an organism’s response to urbanization and it may differ widely on a species by species basis.

              

(Carabidae Caminara: http://commons.wikimedia.org/wiki/File:Carabidae_Caminara_Starred_ground_beetle_(Calosoma%3F).jpg)

            Carabid beetles (ground beetles), the focus of our research, have been studied as a group of organisms that can be used as environmental bioindicators (Rainio et al. 2003). Bioindicators are species that can be observed in order to determine the effects of environmental disturbance in an area. Bioindicators often mirror the responses of other organisms as well as overall biodiversity. In order to try and understand how Grinnell’s Carabid beetle populations are responding to moderate levels of urbanization, we looked at the difference in species richness and diversity between restored prairie habitats on campus and landscaped garden habitats. While each of these habitats is fragmented, one is a remnant of the native Iowa landscape, and one is the result of human landscaping. It will be interesting to compare how ground beetles respond to these two different types of vegetation in a moderately urbanized setting. In accordance with McKinney’s findings, we predict that species diversity and abundance will probably decline in the landscaped areas, which simulate more urbanization, as opposed to the restored prairie, which simulates rural and native areas.

  

                                               (Reconstructed prairie at Grinnell College)

References:

McKinney, M.L. 2008. Effect of urbanization on species richness: A review of plants and animals. Urban Ecosystems 11 (2): 161-176.

Rainio, J., Niemela, J. 2003. Ground beetles (Coleoptera: Carabidae) as bioindicators. Biodiversity and Conservation 12 (3): 487-506.