In a niche-neutral continuum, a set of theoretical models in a metacommunity operates simultaneously in patchy habitats.

Abstract

This study investigated the origins and maintenance of biodiversity by integrating ecological and evolutionary mechanisms into a spatially-explicit synthesis between niche-based processes and neutral dynamics (ND). An individual-based model on a two-dimensional grid with periodic boundary conditions was used to compare a niche-neutral continuum induced in contrasting spatial and environmental settings while characterizing the operational scaling of deterministic-stochastic processes. The spatially-explicit simulations revealed three major findings. First, the number of guilds in a system approaches a stationary state and the species composition in a system converges to a dynamic equilibrium of ecologically-equivalent species generated by the speciation-extinction balance. This convergence of species composition can be argued under a point mutation mode of speciation and niche conservatism due to the duality of ND. Second, the dispersal modes of biota may affect how the influence of environmental filtering changes across ecological-evolutionary scales. This influence is greatest in compactly-packed areas within biogeographic units for large-bodied active dispersers, such as fish. Third, the species are filtered along the environmental gradient and the coexistence of ecologically-different species in each local community in a homogeneous environment is allowed by dispersals in a set of local communities. Therefore, the ND among the single-guild species, extinction-colonization trade-off among species of similar environmental optima and different levels of specialization, and mass effect, such as weak species-environment associations, operate simultaneously in patchy habitats. In spatially-explicit synthesis, characterizing where a metacommunity falls along a niche-neutral continuum is too superficial and involves an abstraction that any biological process is probabilistic; therefore, they are dynamic-stochastic processes. The general patterns observed in the simulations allowed a theoretical synthesis of a metacommunity and explained the complex patterns observed in the real world.