Modelling the role of selection and complementarity in ecosystem function under climate change

Understanding how ecosystem function depends on temperature is important in understanding ecosystem resilience to climate change. The response to warming at a species level is relatively well understood, through the metabolic theory of ecology, which captures the temperature dependence of biological processes. However, when multiple species are present, interactions between the species are important too. Therefore, to understand community function, we must understand the response of the individual species, and the interactions between them. These interactions may depend on temperature, and can be split into two main mechanisms: selection and complementarity. Both of these processes are likely to depend on the number of species present; the biodiversity of the ecosystem. Currently, the response of communities to temperature change, and how changes in diversity may increase or buffer impacts, is poorly understood.

 

Our understanding of ecosystem function can be improved by using mathematical models to constrain the mechanisms underlying key processes. Using data from laboratory experiments, we model communities of heterotrophs responding to temperature change. To model selection, we use a simple model of a community sharing a resource, with parameters measured empirically. Without complementarity, the model underestimates community function. Complementarity is included through a single parameter, which determines to what extent different taxa share the same resource pool. This parameter is difficult to measure directly, so must be fitted using empirical community function data. Through our model, we show that the strength of complementarity within a community depends on both diversity and temperature. Interestingly, we also find that complementarity is strongest at higher and lower temperatures, and more dependent on diversity at medium temperatures.