The effects of prey density on survival and growth of damselfly larvae

Abstract

Abstract. Instar 10, 11 and 12 Ischnura larvae were maintained throughout the instar on a constant food supply (Daphnia magna of a standard size). A very narrow range of prey availability separated cohorts in which all the larvae successfully moulted to the next instar, from those in which all the larvae died (less than one Daphnia per day in the case of instar 10). Larvae were able to survive long periods without food at 16°C. Prey availability had a marked effect on development rates, which continued to increase at prey densities well in excess of 100% survival by the larvae. The data on Ischnura survival and development rates are compared with previously published general models of these two components of the predators' rate of increase. We conclude that starvation is very unlikely to be a significant cause of mortality in the field for Ischnura (or indeed most other Odonata larvae), but that prey availability undoubtedly influences development rates. Natural selection should therefore favour larvae that forage optimally to minimize development times.