Positive interactions and interdependence in communities.

Facilitative interactions play crucial roles in community organization, and the stress gradient hypothesis (SGH) provides a simple conceptual framework for the context-dependency of competitive and facilitative interactions. The idea is that positive interactions are more common under high physical and consumer stress, where species benefit from stress-tolerant neighbors, than in benign environments. We explore insights from the SGH into ecological generality, niche theory, community assembly, and diversity effects on ecosystem function and discuss how the SGH can inform our understanding of rapid evolution, mutualisms, exotic invasions, and facilitation cascades. We suggest that, with escalating global stresses, the SGH may provide a conceptual template for an interdependent perspective in ecology that can contribute to conservation and restoration efforts.