The Odonata of the western Upper Peninsula of Michigan and factors affecting their distribution

Odonates are known to have diverse communities and high densities of individuals. The Ottawa National Forest, occupying 405,000 ha in the western Upper Peninsula of Michigan, has 88 species of the 160 species known from the entire state. The central issue addressed by this research is discovering mechanisms that allow odonate species to coexist as larvae. Habitat is one of several niche dimensions believed to be important in the coexistence of species. Microhabitat preferences of Cordulia shurtleffi and Ladona julia were examined in laboratory and field experiments. In laboratory arena experiments C. shurtleffi was found to prefer leaves and L. julia preferred mud. In the field, L. julia colonized cages with a mud substrate but C. shurtleffi did not show a significant preference for mud or leaves. The role competition plays in microhabitat choice was examined with laboratory experiments. When combined in laboratory arenas, neither C. shurtleffi nor L. julia competitively forced the other species from a suitable microhabitat into an unsuitable one. However, when introduced into arenas divided into mud and leaf substrates, C. shurtleffi favored the leaves and L. julia was found in the mud. Longer duration experiments with L. julia and Epitheca spinigera that included prey additions yielded similar results. Physical and chemical factors affecting odonate distribution were examined using multivariate techniques. Stream, bog, and eight lake site groups were delineated based on their odonate communities species. Substrate type and vegetation appeared to have the greatest influence on odonate distributions. Larval lifestyle was examined to determine its role in species coexistence by studying the activity and microhabitat preferences of L. julia and C. shurtleffi under different light conditions. L. julia demonstrated traits that placed it in the slow lifestyle. C. shurtleffi behavior was more flexible but still conformed to a slow lifestyle, suggesting their common co-occurrence is not due to differing lifestyles. Taken together, these results suggest that different microhabitat preferences, and the complex interactions resulting from semivoltinism may be most important in the coexistence of northern odonate species.