Effects of temperature on consumer control and food web structure: Theoretical predictions and empirical tests in planktonic food webs

Background/Question/Methods Climate change is shifting environmental conditions in ecosystems worldwide, yet most investigations of climate change effects on ecosystems lack a theoretical framework for understanding how ecological structure and function will change.  We present a theoretical framework for understanding how two key climate-related factors, temperature and resource supply, will affect food web structure and function. This framework is based on general constraints of temperature on heterotrophic and autotrophic metabolism and draws upon the Metabolic Theory of Ecology and classic consumer-resource theory.  First, using simple consumer-resource models, we develop predictions for how metabolic temperature scaling affects herbivore and primary producer biomass. Second, we test these predictions using data from experimental planktonic food webs and field observations of plankton abundance through time in the North Atlantic Ocean. Finally, we outline future directions for the development of a theoretical framework for understanding the effects of climate change on marine food webs. 

Results/Conclusions The combined metabolic theory / consumer-resource models show that in the short-term, warming can strengthen consumer control and shift food web structure toward increased herbivore biomass.  This result was robust to different model formulations, but dependent on adequate nutrient enrichment.  In the long-term, however, models predict that warming causes a decline in consumer biomass with either a similar decline or no change in primary producer biomass. Experimental data are consistent with the model predictions, and this exercise illustrates how metabolic theory may be applied to complex ecological systems. With further development, this framework will provide a powerful tool for predicting the effects of climate change on carbon cycling and consumer productivity in marine ecosystems.