Ecological specialization of mixotrophic plankton in a mixed water column

Ecological specialization is an important process underlying the self-organization of ecosystems. Insight into this process leads to a better understanding of the structure and functioning of the real and complex ecosystems surrounding us. In an article in the September issue of The American Naturalist, Tineke A. Troost and colleagues address these fundamental issues, while focusing on a simple but common aquatic system.

Their research integrates three separate threads of modern ecological theory: spatial dynamics, evolutionary branching, and mixotrophy and shows that the environmental heterogeneity caused by a light-intensity gradient can induce a population of generalists (mixotrophs) to split into trophic specialists (pure autotrophs and pure heterotrophs), though this is not possible in a homogeneous environment.

Previous research had shown that environmental gradients favor evolutionary branching, but the underlying reasons for branching and the resulting community structure are quite different in the present study. Introducing spatial heterogeneity also makes the evolution of the population sensitive to other environmental conditions, such as total nitrogen content or light intensity. As such, it provides an explanation of why mixotrophs are often more dominant in nutrient-poor systems while specialist strategies are associated with nutrient-rich systems.