Dynamics of abundance of experimental populations of Daphnia longispina (O.F. Müller, 1785) at stepwise changes in temperature

Abstract

Although many studies demonstrate the advantages of rhythmic fluctuations of factors compared to constant regimes, the effect of arrhythmic changes in temperature has not been studied in detail [1‐3], despite the fact that organisms inhabiting both intact and thermally changed aquatic ecosystems may be exposed to rapid and sometimes unpredictable fluctuations in temperature. This work is devoted to studying the dynamic characteristics that facilitate or limit the optimal living conditions of populations. The purpose of this study was to reveal and describe the effects of nonperiodic stepwise changes in temperature varying in amplitude and direction on the dynamics of abundance of experimental populations of Cladocera by the example of Daphnia longispina from the Rybinsk Reservoir littoral. This is the first study to demonstrate that, other conditions being equal, nonperiodic stepwise changes in temperature in the range 16.3–25.1°e can exert direct and delayed stimulatory and direct inhibitory effects on the dynamical of abundance of Cladocera populations. For analysis we used the results of chronic (63-daylong) experiments in microcosms (aquariums, volume 45 l), during which the responses of populations of dominant zooplankton species to graded changes in temperature were studied.