Diet Mixing: Do Animals Integrate Growth or Resources across Temporal Heterogeneity?

Animals commonly experience spatial and temporal variation in resource quality, thus experiencing temporally variable diets. Methods for scaling up growth in component patches to long-term growth across heterogeneity are seldom explicitly considered. Longterm growth is sometimes considered to be a weighted average of growth rates on component diets (growth integration). However, if animals integrate resources across high-and low-quality diets, their long-term growth may be greater than predicted from diet-specific growth rates (resource integration). We measured biomass growth rates of seven Daphnia species exposed to different types of diel variation in algal phosphorus (P) content. Support for resource integration was found for four of the seven species, which achieved near maximal growth when high-P food was available for at least 12 h. In contrast, no support for resource integration was found for the other three species. These three species achieved only one-half maximal growth rate under the same conditions and could be considered growth integrators. The type of integration could be predicted from the degree of stoichiometric homeostasis. Species with weak homeostatic regulation exhibited a capacity for resource integration. Resource integrators should have an advantage in heterogeneous environments.