A ten year study of the odonate assemblage of Bays Mountain Lake, Tennessee

Bays Mountain Lake (NE Tennessee, USA) is a 15 ha shallow, eutrophic impoundment with relatively stable water level and well-developed littoral vegetation. Between July, 1977, and June, 1987, larval Odonata were sampled monthly by sweep-net from five habitats in the lake. Several lines of evidence developed from these data indicate that this assemblage has a persistent structure, relatively low variabilities of population densities, and is stable. The evidence includes long-term persistence of the dominant taxa, typical standard deviations of the logarithm of population sizes, high and significant year-to-year rank concordance, and few significant correlations of log density with time. Only three species shifted strongly in relative abundance during the ten-year study: Dromogomphus spinosus colonized the lake during this period; Celithemis fasciata was only abundant during the first two years; and Tetragoneuria cynosura declined over the period (r= -0.81, P<0.01). Some of the ecological mechanisms underlying the constancy and stability of this odonate assemblage have been identified from diet analyses, laboratory behavior studies, and field enclosure experiments. Prominent among these mechanisms are interference competition (including mutual predation) among larvae, and predation and competition by insectivorous fish.