A trait-based perspective of temperature effects on species interactions

Background/Question/Methods

Understanding how temperature influences population dynamics and species interactions is an important question, not least because mounting evidence for climate warming makes it imperative that we be able to predict how species respond to warming and whether they can adapt fast enough to withstand its effects.  Here we develop a theoretical framework for elucidating temperature effects on competition that integrates mechanistic descriptions (derived from first principles of thermodynamics) of temperature effects on biochemical processes (e.g., reaction kinetics, hormonal regulation) that underlie life history traits (reproduction, development, survivorship) into population models (constructed using delay differential equations) that realistically capture the variable developmental delays characteristic of ectotherm life cycles.  This framework yields testable comparative predictions about how temperature effects on life history traits influence density-dependent feedback loops within and between species, and how these effects translate into the dynamics of species interactions.

Results/Conclusions

We report two key findings.  First, ectotherm population regulation depends crucially on the mechanisms by which temperature affects intra-specific competition.  When competition is strongest at temperatures optimal for reproduction, effects of temperature and competition act antagonistically, leading to more complex dynamics than when competition is temperature-independent.  When the strength of competition increases with temperature past the optimal temperature for reproduction, effects of temperature and competition act synergistically, leading to dynamics qualitatively similar to those when competition is temperature-independent.  Paradoxically, antagonistic effects yield a higher population floor despite greater fluctuations.  Second, the mechanism by which temperature affects intra-specific competition also determines whether warming stabilizes or destabilizes consumer-resource interactions. When the strength of self-limitation increases monotonically with temperature, warming causes a decrease in consumer-resource oscillations. However, if self-limitation is strongest at temperatures physiologically optimal for resource reproduction, warming can increase consumer-resource oscillations. Importantly, whether warming causes consumer extinction or destabilizes consumer-resource dynamics depends crucially on whether the consumer is a thermal generalist or a specialist compared to the resource species.