Trophic interactions and temperature change: Using interaction strength to predict stability and productivity
With global climate change, it is critical to understand how small changes in environmental temperature affect interacting species. The integration of temperature into theory on consumer-resource interactions can provide this understanding and build a framework for how species interactions are influenced by abiotic changes. Developing an integrated theory promises to strengthen quantitative and conceptual approaches to climate change ecology.
Temperature changes can have large direct and indirect impacts on species, altering both the production and stability of ecological communities. Direct effects have been characterized by species’ thermal response curves, which are increasingly understood for a wide range of species. Indirect effects arise from sensitivity of species interactions, such as trophic interactions, to temperature. These indirect effects have been characterized by their unpredictability; they range from negligible to more important than direct effects, and there are no general frameworks for understanding when and how they will be important. Our research focuses on indirect effects in trophic interactions to: 1) build a framework that allows us to predict when indirect effects will be important in food webs experiencing changing temperatures, 2) incorporate direct effects into this framework, thereby allowing ecologists to use the well-developed literature on physiological responses to temperature, and 3) use this framework to predict how and when indirect effects will influence food web production and stability.
Our framework uses the building block of food webs, Consumer-Resource (C-R) interactions. We develop a general measure of interaction strength based on the coupling of C-R interactions and on the overall fluxes into and out of a C-R module. Specifically, our interaction strength measure incorporates the production of the resource and relative growth rate of the consumer. This measure is distinct from theoretical measures of interaction strength, but is commonly quantified in ecological studies. We show how our interaction strength measure can be used to generate predictions about how temperature will influence the stability of C-R interactions and the absolute and relative abundances of the consumer and resource. We decompose the measure into its components to express it in terms of the thermal response curves of species’ vital rates, such as consumer mortality and consumption rates. This relationship between interaction strength and vital rates allows us to highlight trophic interactions that are likely to produce strong indirect effects following warming.