The influence of temperature and food chain length on plankton predator-prey dynamics

With recent predictions for global climate warming, the question arises as to how changes in temperature influence the dynamics of populations in natural communities. We investigated the effect of temperature (18 and 25 degrees C) on the stability of a common freshwater predator-prey system consisting of Daphnia pulex and phytoplankton in different types of mesocosm communities. The plant-herbivore dynamics were examined in the presence and absence of the predator Mesostoma ehrenbergii to simulate food chains of two or three trophic levels, and in the presence or absence of competing zooplankton. The predator-prey system was destabilized at the higher temperature in all types of communities, and D. pulex extinction always occurred. This result was unaffected by simplification of the community but was enhanced by the addition of the carnivore. Mechanisms are proposed for the observed results including (i) the direct effect of temperature on vital rate parameters describing the D. pulex - algal interaction and (ii) a shift in algal community structure to less edible species following suppression by the herbivore at the higher temperature. Some implications of temperature increases expected under current global warming scenarios in pond systems are discussed.