Effects of Temperature on Intraspecific Competition in Ectotherms

Abstract

Understanding how temperature influences population regulation through its effects on intraspecific competition is an important question for which there is currently little theory or data. Here we develop a theoretical framework for elucidating temperature effects on competition that integrates mechanistic descriptions of life-history trait responses to temperature with population models that realistically capture the variable developmental delays that characterize ectotherm life cycles. This framework yields testable comparative predictions about how intraspecific competition affects reproduction, development, and mortality under alternative hypotheses about the temperature dependence of competition. The key finding is that ectotherm population regulation in seasonal environments depends crucially on the mechanisms by which temperature affects 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. These findings have important implications for predicting effects of climate warming on population regulation. Synergistic effects of temperature and competition can predispose populations to stochastic extinction by lowering minimum population sizes, while antagonistic effects can increase the potential for population outbreaks through greater fluctuations in abundance.

From individuals to populations: How intraspecific competition shapes thermal reaction norms

“…We fail to show any increase of the strength of competition above 11°C. Thus, our results do not support the first scenario mentioned above (Amarasekare & Coutinho, ).…”

“…Within‐species genetic variability can add another level of complexity to this interaction between temperature and competition: the strength of competition and the way it varies with temperature can vary between different lineages or populations. A variation in the shape of this intraspecific‐competition thermal reaction norm could be associated with different demographic responses as mentioned above (Amarasekare & Coutinho, ).…”

“…In this second scenario, direct and indirect effects will act antagonistically: above the thermal optimum, warming will have a direct negative effect but an indirect positive effect due to the loosening of the strength of competition with increasing temperatures. This is expected to generate more complex demographic responses (Amarasekare & Coutinho, ). Note that for temperatures below the optimal temperature (where the TSR is defined), the two hypotheses have the same predictions as direct and indirect effects always act antagonistically.…”

Exploring the role of temperature in the ocean through metabolic scaling

“…Differential temperature scaling of individual-level biological rates influences the outcomes of species interactions (Amarasekare andCoutinho 2014, Gilbert et al 2014), and potentially community structure and dynamics (Rall et al 2010, Lemoine and Burkepile 2012, Iles 2014). For example, metabolism and attack rate appear to scale more directly with temperature than consumption, resulting in reduced ingestion efficiency (or the ratio of carbon assimilated per carbon respired) and potentially decreased consumer fitness and density with warmer temperatures (Rall et al 2010, Englund et al 2011, Lemoine and Burkepile 2012, Iles 2014.…”

“…These results are opposite to short-term effects of warming that reflect only per capita growth and no population dynamics. Thus, the signal of metabolic scaling on species interactions over a temperature gradient depends on several factors, including resource supply, the dynamics of the consumer-resource system, and the time scale of observation , Amarasekare and Coutinho 2014, Gilbert et al 2014). An important component of recent MST research has been to incorporate and quantify other abiotic and biotic covariates in models and experiments to better understand how temperature scaling of performance affects the abundance of species whose density is regulated by species interactions or resource limitation, i.e., Lo´pez-Urrutia et al (2006) (2011) and Gilbert et al (2014) incorporated resource availability.…”