8 September 2006 Progress Report, Alysa Remsburg
During June through August 2006, I collected Odonata community and behavioral data to address several ecological questions on the role of vegetation structure. To test whether odonates select breeding habitats based on the presence of at least a small riparian buffer, I observed adult dragonfly responses to potted cattails (Typha minima) at four (15 m 2 ) developed lakeshore study sites. Using study days as experimental replicates, I found that damselflies (suborder Zygoptera) were more abundant at lawn sites when the cattail buffer was present (mean = 6.0 damselflies, standard deviation = 3.7) than when the potted cattails were removed from the lawn sites (mean = 3.3 damselflies, standard deviation = 2.4; paired t-test t = -3.5, df = 17, p = 0.003). Total dragonfly abundances did not vary with the cattail buffer, although further analyses of particular species (especially in the Libellulidae family) may reveal significant differences based on the buffer treatment. Unfortunately, odonates deposited eggs too infrequently for assessment of relationships between the cattail buffer and oviposition occurrence. However, based on adult abundance data (from 2006), increased oviposition rates at buffered sites very likely account for higher Odonata diversity and density recorded previously (2004 and 2005) at sites with shoreline cattails or tall sedges.
After identifying larval species collected from 6 sites in 2004, 2005, and 2006, I hope to track changes in odonate communities that may result from changes to the riparian vegetation accompanying home construction at the sites in 2004. Throughout the summer of 2006, I also collected the cast-off skins of odonate larvae emerging from the lakes at 20 sites. Because I already have data from the larvae occurring at those sites in 2005, I will be able to investigate whether the number of dragonflies successfully emerging varies with the type of shoreline vegetation. |
