Mechanisms promoting biodiversity in ecosystems

Explaining biodiversity has been a central focus in theoretical ecology, yet the Competitive Exclusion Principle (CEP) poses a significant challenge. According to the CEP, when two species compete for the same resource, they cannot coexist at stable population densities. More generally, the number of consumer species cannot exceed the number of resource species at steady-state. However, competitive exclusion is rarely observed in natural ecosystems. For instance, in aquatic ecosystems, a limited variety of resource species supports hundreds or more species of plankton. This phenomenon, known as “the paradox of the plankton,” clearly contradicts the CEP. Consequently, explaining species diversity has become a major focus in ecology. In 2005, Science listed “what determines species diversity” as one of the 125 most important questions in science.

Recently, a review entitled “Mechanisms promoting biodiversity in ecosystems”, published in Quantitative Biology, introduces the latest advancements in mechanisms that promote biodiversity. The authors provide a systematic review of theoretical mechanisms that break the constraint of the CEP by classifying existing theories into two categories. The first category includes mechanisms that liberate the constraint of the CEP through contextual differences, such as those introducing temporal variations, spatial heterogeneity, and self-organized dynamics in a stable environment. (Fig. 1). These mechanisms break the limitations of the CEP by bypassing the assumptions of “well-mixing” and “steady state.” The second category breaks the CEP in its original context, involving well-mixed systems and steady states. All of these are pairwise encounter models based on mean-field theory in statistical physics, such as mechanisms involving chasing triplets and the mean-field model of intraspecific predator interference (Fig. 2).