Scaling relationships for the temperature-dependence of species performance

Background/Question/Methods

Environmental temperature affects individual physiology and influences traits such as metabolic rate, body velocity, and handling time. We present a meta-analysis of a comprehensive database for the temperature response of traits that range from heart rate to consumption rate. Complementary to this, we present a modeling framework for the thermal response of pairwise consumer-resource interactions and specifically consumption rate. The ultimate goal is to scale up from these pairwise interactions to more general trophic interactions and eventually entire food webs. Using our model, we also derive predictions for the effect of temperature on equilibrium population densities. Our model emphasizes the role of asymmetries between temperature responses for different traits, different species, different foraging strategies, and different thermy (e.g., ectotherm versus endotherm). In particular, our models can apply to several types of foraging strategies, including active-capture (both consumer and resource velocity are important), sit-and-wait (resource velocity dominates), and grazing (consumer velocity dominates). In our models we include the drivers of trophic interactions, such as environmental temperature and habitat heterogeneity, and for the individuals and species involved in these trophic interactions, we include characteristic traits, such as body size, foraging strategy, and thermy. These drivers and traits are often known or straightforward to measure. Consequently, our framework represents a step towards more accurate predictions for the thermal dependence of food-web and ecosystem dynamics, including how natural systems will respond to current and future temperature change.

Results/Conclusions

We present results from an analysis of the temperature responses for 309 species that span about 40^o C, 15 orders of magnitude in body size, and live in terrestrial, marine, and freshwater habitats. Combining our meta-analysis of data with our modeling efforts, we conclude that temperature drives pairwise consumer-resource interactions primarily through its effects on body velocity because this trait strongly determines how often consumers and resources encounter each other. We argue that this qualitative conclusion (but not necessarily the quantitative predictions) should apply more generally to trophic interactions and food webs. Using our theoretical framework and data analysis, we identify three important types of asymmetries in the temperature responses of traits associated with trophic interactions among consumers and resources: i) different magnitude of response, ii) different rates of response, and iii) different peak trait value and corresponding optimal temperatures.