Energy budgets and reproductive ecologies of mayflies occupying disparate thermal environments

Energy budgets were calculated for two populations of Ameletus occupying thermally disparate habitats. Growth, consumption, respiration, fecundity, and energy content of larvae and eggs were determined experimentally. Respiration rates increased and decreased with temperature throughout the life cycles of both species, although thermal effects became less pronounced with increased body size. Ameletus similior exhibited more uniform and consistently higher respiration values than Ameletus celer. Respiration costs were not constant over the life cycle of either species as has been reported for some other mayflies. Growth was influenced by both temperature (which affected instar duration) and body size (which affected growth ratio). Growth corresponded positively to temperature in both species, but was more uniform in A. celer. Net growth efficiency and assimilation were highest during cold periods in A. celer, but highest during warmer periods in A. similior. Consumption estimates were high even after adjustments for projected nonfeeding time, but unless food availability or handling time is limiting, the feeding rate of Ameletus relative to body mass may be higher than rates reported for other aquatic insect larvae. Several sources of error in consumption estimates existed, however. Assimilation efficiencies were low, but comparable to those for other herbivorous aquatic insects. Reproductive effort was higher in A. celer, but net reproductive effort was lower. The higher net reproductive effort by A. similior did not result in increased fecundity as expected, but in higher egg energy content. This and other factors suggest that A. similior displays more "K-selected" traits than A. celer, and indicates that greater fitness may not necessarily be synonymous with higher fecundity in all mayflies in all habitats.