COS 60-1 - Facilitation and functional trade-offs explain community responses to multiple stressors

Abstract: The co-tolerance concept has been often cited as a tool for examining community responses to multiple adverse environmental changes based on the correlation of its species tolerances of such stressors. Nevertheless, the co-tolerance approach to community ecology remains in need of empirical validation and refinement as it lacks consideration of the potential importance of stress-induced interactions between species (e.g., facilitation) and their individual functional traits. To explore the potential influence of species interactions on community co-tolerance, eight species were exposed both individually and assembled together to two stressors to determine whether correlation of their fundamental or realized tolerances better predicted changes in species richness and total biomass. Four species realized positive responses to the stressors when grown together, supporting the stress-gradient hypothesis of facilitation. Positive correlation of species responses to the two stressors resulted in a less than expected net loss of species richness, supporting the co-tolerance approach. However, it failed to predict the greater than expected negative effect of the stressors on community biomass because of the functional trade-off involving greater tolerance at a cost of lower productive capacity. Our findings highlight how integration of species interactions and their traits into the community co-tolerance approach can advance its use in multiple stressor ecology.