Modeling community assembly on growing habitat “islands”: a case study on trees and their vascular epiphyte communities

Abstract

The number of available sites for establishment is a key determinant of species richness on habitat islands. While most theoretical studies assume habitat size or capacity to be constant, many natural habitats are characterized by dynamic growth in capacity over ecological timescales. A case in point is provided by trees that serve as habitat for vascular and non-vascular epiphytes. Here, we develop a modeling framework, based on neutral theory, to address the effects of habitat growth on community development, i.e., species richness and abundance. The model is parameterized to the situation of vascular epiphyte communities in tropical lowland forests and includes stochastic reproduction, death, and immigration events from a larger metacommunity. Using numerical simulations, we explore the proportion of growing sites occupied by individuals, the number of empty unoccupied sites, as well as changes in species abundances, species richness, colonization and extinction rates, and the dependence on the abundance in the metacommunity throughout the growth of the habitat. Our analysis suggests two characteristic phases of community development in a growing habitat: (i) an initial phase, characterized by a rapid buildup of empty sites, a slow increase in species abundance, and a fast increase in species richness, and (ii) a second phase, in which the number of empty sites reaches an equilibrium, species richness is accumulating very slowly, while the number of individuals increases unabatedly with habitat capacity.