EFFECTS OF LOCAL AND REGIONAL PROCESSES ON BIOLOGICAL DIVERSITY: SATURATION AND OPENNESS OF COMMUNITY ASSEMBLY

The publication of the equilibrium model of island biogeography by MacArthur and Wilson (1963) initiated a paradigm shift in community ecology that focuses on biodiversity. Community assembly as the core mechanism of determining biodiversity has been re-examined from a larger-scale perspective by linking to biogeography. Being different from classical community ecology, the new paradigm-based community ecology regards local communities as an open unit, and species dispersal and migration within regional- and meta- communities acting as the key forces to balance local species extinction. The species composition and diversity of local communities result from the interaction between local and regional processes. Regional processes include geographical, historical, and evolutionary factors that affect speciation and diversification of species. The relative importance of local versus regional processes in community assembly is temporal and spatial scale dependent. This review first briefly retrospect the shift in community ecology paradigms over the past half century, and then systematically introduces the concepts of community assembly, species pools, and community saturation, followed by methods for analyzing the relative importance of regional and local processes based on local-regional relationships for species richness. We also discuss potential issues and introduce further analytical methods for these issues. Species pools are a basic concept of biogeography. The number and composition of species in a species pool record the ecological and evolutionary processes that have occurred historically in at geographical or regional scales. The species pool concept allows us to quantitatively describe the role of regional processes. A local community is a subset of all species in a regional species pool, and local community assembly refers to the processes and mechanisms of the formation of this subset. The local-regional relationship for species richness provides an empirical approach to determine the relative importance of regional and local processes in community assembly. As the curvilinearity of this relationship spatial scale, environmental conditions, and species characteristics, additional theoretical and empirical methods are needed to interpret the community saturation. When the local scale is small enough, community saturation in species at the same trophic level can be detected with greater sensitively. For communities that consist of species at multiple trophic levels, the interactions between different trophic levels must be carefully considered to interpret the local-regional relationships for species richness. Environmental selection and interspecific interactions play on traits rather than species. The comparison of functional diversity between observed and random communities can reveal the type and intensity of local processes. We emphasize that, to reveal community assembly and the maintenance of biodiversity, it is necessary to accurately define the species pool and incorporate both the size and functional attributes.