  Ecosystems are formed by networks of species and their interactions.
Traditional models of such interactions assume a constant interaction strength
between a given pair of species. However, there is often significant trait
variation among individual organisms even within the same species, causing
heterogeneity in their interaction strengths with other species. The
consequences of such heterogeneous interactions for the ecosystem have not been
studied systematically. As a theoretical exploration, we analyze a simple
ecosystem with trophic interactions between two predators and a shared prey,
which would exhibit competitive exclusion in models with homogeneous
interactions. We consider several scenarios where individuals of the prey
species differentiate into subpopulations with different interaction strengths.
We show that in all these cases, whether the heterogeneity is inherent,
reversible, or adaptive, the ecosystem can stabilize at a new equilibrium where
all three species coexist. Moreover, the prey population that has heterogeneous
interactions with its predators reaches a higher density than it would without
heterogeneity, and can even reach a higher density in the presence of two
predators than with just one. Our results suggest that heterogeneity may be a
naturally selected feature of ecological interactions that have important
consequences for the stability and diversity of ecosystems.
