Life history and resource partitioning among the odonates of a Northern Illinois farm pond

Bibliography: pages 184-193.Life history characteristics of odonate larvae were examined in a northern Illinois farm pond from September of 1979 to November of 1980. Odonate larvae sere sampled to a depth of 150 cm over a 15-month period. Fifteen species from a total of 4831 odonate larvae were collected from 675 Eckman grab samples. The greatest densities occurred during the fall, whereas the lowest densities occurred during July. Flight periods of adults of some species varied from recorded flight periods. For portions of the year, species appeared to be partitioned into groups based on larval head width. Head width was found not to be a good predictor, among species, of instar class. Less than 5% of the larvae were spring species as opposed to summer species. The mean depth for all larvae on all dates was 71.9 cm. Species appeared to be divided into four groups based on depth. The mean depth of each species varied seasonally suggesting that the larvae were migrating to deeper water during the late summer and fall and back to shallow water in the spring. The timing of this migration varied between the instar classes of some species resulting in instar class separation by depth. The migration occurred in three discrete phases. Migrations to deeper water occurred in the late summer, and again in the late fall. The former migration may be a response to fish predation and the latter to water temperature change. The third migration, to shallow water in the spring, was probably due to older instars moving to shallow water to emerge as adults. The different species of odonates were not distributed uniformly in the different types of vegetation. Species also differed in their habit. In this study, it was not until five niche ares were considered simultaneously that the species exhibited sufficient niche separation to suggest resource partitioning as an explanation for coexistence of the species. These niche axes were depth, head width, time, habit, and vegetation association.M.S. (Master of Science