Metabolic scaling theory predicts how temperature affects consumer-resource dynamics. However, a major assumption of metabolic scaling theory is that nutrient supply is non-limiting. Yet in nature, changes in nutrient supply to primary producers often occur simultaneously with warming. We still do not know how variable nutrient supply modifies the temperature dependences of consumer-resource dynamics. Using an experimental Daphnia-phytoplankton mesocosm system, we asked: Does phosphorus limitation change the temperature dependence of consumer and resource population growth rates and abundances, relative to predictions that assume no nutrient limitation?
Results/Conclusions
We found that nutrient limitation increases the temperature dependence of resource growth rates, causing deviations from predictions based on the activation energy of photosynthesis. As predicted by metabolic scaling theory, carrying capacity of the resource declined with increasing temperature under non-limiting nutrient conditions. This temperature effect was magnified by nutrient limitation. Further, consistent with theory, in nutrient replete systems consumers reduce temperature dependence of resource growth rates, altering outcomes relative to predictions based on consumer-free systems. In contrast, temperature dependence of consumer abundances were consistent when nutrients were reduced equally across all temperatures. However, the absolute abundances of consumers were consistently lower under nutrient limitation, implying that if temperature and nutrient supply covary, the net temperature dependences of consumer abundances will be increased. This means that at the community level, the effects of temperature may be greater than expected in nutrient limited ecosystems.