FISH-MEDIATED ALTERNATIVE LIFE-HISTORY STRATEGIES IN THE DRAGONFLY EPITHECA-CYNOSURA

We investigated the potential impact of predation on life-history traits of aquatic insects by examining various factors affecting the voltinism pattern of Epitheca (Tetragoneuria) cynosura (Say) in Bays Mountain Lake, Sullivan County, Tennessee, USA. We observed the growth of individual Epitheca protected from competition and predation in small (0.03 m2) in situ enclosures. Approximately 70% of the larvae followed univoltine development; this contrasts sharply with earlier studies in Bays Mountain Lake where only 25% of emerging imagoes were thought to be univoltine. We also conducted a study of the diets of large sunfish to identify the predator with the greatest potential impact on Epitheca population densities. Redear sunfish (Lepomis microlophus) consumed large numbers of Epitheca during mid-July, and the dragonflies consumed were larger than expected based on size-distributions found in the lake. In fact, those eaten were often from sizes identified as potentially following univoltine development, suggesting that predation from large fish could reduce the success of the univoltine strategy. We also conducted an experiment in small (0.15 m2) in situ enclosures to examine competition between small sunfish and Epitheca. We found that while small sunfish had little influence on larval survival, larvae grew more slowly in their presence than in their absence. Thus small sunfish potentially hindered the ability of larvae to develop in a univoltine manner. Lastly, we conducted an experiment in large (24 m2) enclosures to test hypotheses generated by the studies above. Small sunfish produced a statistically significant reduction in the ratio of univoltine to semivoltine Epitheca larvae; and both large and small fish decreased the number of successfully emerging univoltine Epitheca. These studies show that in the absence of potentially deleterious biotic interactions, most Epitheca larvae in Bays Mountain Lake follow univoltine development; but competition and predation from sunfish result in lowered success of the univoltine strategy.