The prevalence of reported “ecological surprises” in a rapidly changing world attests to the lack of reliable predictions of the cumulative impacts of multiple stressors. While the Species Co-Tolerance Concept (SCC) is often cited for how the relatedness of species tolerances to different stressors (i.e. co-tolerance) may explain community responses to multiple stressors, its lacks proof of concept. Further, the roles of interactions among species have not been incorporated into the SCC, thereby possibly limiting its ecological relevance. We stressed eight freshwater algal monocultures both individually and assembled together to discover that realized rather than fundamental species co-tolerances better captured the combined effects of two stressors (acidification and heating) on the whole community.
Realized co-tolerances of certain species were stronger than their fundamental co-tolerances, highlighting facilitative interactions when under stress. Species that realized greater co-tolerance however did not compensate for the more sensitive and productive species. Our testing of the SCC refined it for the first time by demonstrating that it is essential to account for species interactions when forecasting community responses to multiple stressors. The SCC may now be more applicable to predicting the effects of multiple stressors on communities when historical data exist showing species realized tolerances of individual stressors.