The effect of temperature on the dynamics and functioning of microbial communities

Abstract

Temperature is arguably the most important environmental driver in ecological systems. It acts across multiple scales to affect everything from individual physiological rates to populations dynamics and the functioning of ecosystems. Despite this, there is still uncertainty surrounding the mechanisms through which temperature acts, especially on microbial communities whose contributions to the cycling of energy and nutrients make them a crucial part of global biogeochemical cycles. In this work I use mathematical modeling and empirical data to investigate the effects of temperature on microbial communities and their emergent structure, dynamics and functioning. I focus particularly on two features of microbial communities and how they modify this response, interactions between populations and the variation in thermal responses between different taxa. I first examine the effects of temperature on the feasibility of microbial communities. Using a general model of community dynamics I show how the effects of temperature on populations and their interactions can predict species richness across temperature gradients. Crucially I reveal the importance of variation in thermal sensitivity between populations in determining the shape of this relationship. I then look at the effects of temperature on respiration in microbial communities, using a model of interaction-driven community dynamics combined with microbial microcosm experiments. I show theoretically how interactions can dampen or amplify the sensitivity of community respiration depending whether they are competitive or facilitatory in nature and that these predictions are matched in an experimental microbial heterotroph system. Finally I look at the effects of temperature on functioning and richness in more complex models of microbial communities that explicitly include competition and facilitation via the exchange of metabolic byproducts. I show how increases in temperature consistently lead to the break down of facilitation in microbial communities leading to simplified structure and reduced richness. Overall my work demonstrates how both interactions and variation in thermal responses between taxa can have large impacts on the thermal responses of microbial community properties.