Ephemerella Mayflies of White Clay Creek: Bioenergetic and Ecological Relationships Among Six Coexisting Species

Comparative data are presented on feeding, growth, respiration, mortality, adult emergence and fecundity, egg development, and calorimetry for Ephemerella subvaria, E. dorothea, E. verisimilis, E. funeralis, E. serrata, and E. deficiens in White Clay Creek (WCC), Pennsylvania, USA. All species are univoltine in WCC. The larvae of most species hatch from eggs in late summer—early fall and complete their growth by the following spring or early summer. The magnitude and rate of larval growth for each species appears to be affected largely by seasonal variation in both stream temperature and food quality. Net growth efficiencies (NGE) tend to be positively correlated with larval size for most species. NGE ranged from 3.5 to 81.6% for Ephemerella species. The timing of adult emergence and the size and fecundity of adults appears to be determined largely by the magnitude and pattern of temperatures that are experienced during the larval growth period. An hypothesis is presented to explain the interaction of temperature, insect developmental processes, and physiology in determining both the timing of adult emergence and the resultant size and fecundity of individuals. Empirical data are presented to support the hypothesis. Quantitative data concerning seasonal variation of larval densities are given for all species except E. funeralis. Results indicate that the remaining five species all coexist in riffle habitat in WCC (as opposed to pool habitat). There is also minimal overlap in the relative abundance of consubgeneric species. It is suggested that competition between pairs of consubgeneric species may be reduced somewhat by having the relative abundance and body size, as well as resource requirements (i.e., biomass production), of each pair segregated temporally.