Advances in species coexistence theory

How species coexist locally is a fundamental question in community ecology. Classical coexistence theory underscores the importance of niche differentiation between species and focuses on specific coexistence mechanisms. Studies on these specific coexistence mechanisms have profoundly contributed to understanding species coexistence at the local scale and inspired ecologists to create a more general contemporary coexistence theory. Under the contemporary coexistence theory, species differences are categorized into two groups: niche differences and average fitness differences. Niche differences serve as stabilizing mechanisms that promote species coexistence, whereas average fitness differences are related to equalizing mechanisms that drive competitive exclusion. In this paper we provide a detailed review of contemporary coexistence theory, including its definition and theoretical models, empirical tests of these models and their applications to biodiversity studies. Coexistence theory has applications in a number of other areas including biodiversity conservation and management in a changing world beyond the basic concept of how communities are structured. We show how contemporary coexistence theory has advanced the niche-based classic coexistence theory, helping us to better understand the underlying mechanisms of community assembly and biodiversity maintenance.