DETERMINATION OF SPECIES COMPOSITION IN THE ENALLAGMA DAMSELFLY ASSEMBLAGES OF PERMANENT LAKES

One group of Enallagma (Odonata: Coenagrionidae) is found as larvae only in Michigan lakes containing fish, while the remaining species are found as larvae only in fishless lakes. Dragonfly larvae were the most abundant invertebrate predator group in both lake types, with each lake type supporting a characteristic set of dragonfly species, as in the damselflies. Fish were also potentially major predators in lakes containing fish. Also, Enallagma densities in both lake types were among the highest reported in the literature, suggesting that density-dependent competitive interactions may potentially contribute to maintaining the Enallagma species distributions. Experiments demonstrated that predation by large dragonflies in fishless lakes and predation by fish in fish-containing lakes are 2 major environmental factors maintaining the Enallagma species distributions. Density-dependent competitive interactions among the Enallagma species were only apparent in the fishless lakes, affected species from both groups similarly, and altered their growth but not their survival. -from Author