Temperature determines the effect of energy on diversity in aquatic microcosms

Temperature and energy are important determinants of species diversity, yet their effects on communities are rarely separated experimentally. We present results from an experimental manipulation of temperature and the quantity of organic energy in aquatic microcosms. We show that the effect of energy on species richness and community composition depended upon the temperature at which community development took place and changed through time following community establishment. At 15°C there was a positive effect of energy on species richness throughout the experiment. At 20°C the effect of energy on species richness was initially positive, but later became negative. Different combinations of temperature and energy led to very different species assemblages, with communities in some temperature-energy combinations having extremely deterministic extinction trajectories and those in others being more variable. Understanding how temperature and energy can affect ecological communities separately, as well as through their combined effect on productivity, is important if the consequences of changes to temperature and energy are to be predicted.