COMPUTER SIMULATIONS OF PLANT BIODIVERSITY IN STABLE AND UNSTABLE ENVIRONMENTS: A TEST OF THE NEUTRAL BIODIVERSITY THEORY

The Neutral Biodiversity Theory (NBT) argues that community-level patterns are not determined by trait differences among species, but rather by demographic stochasticity. If true, deterministic patterns of species co-existence, transient or otherwise, should not occur. We tested this critical prediction using a spatially explicit, reiterative algorithm (SERA) that incorporates demographic stochasticity to examine how artificial plant species compete for light and space. An additional level of ecological realism was added by simulating species competition in heterogeneous and disturbed environments. Across 108 simulations, small niche differences influenced interspecific competition and persistence, particularly in spatiotemporally heterogeneous environments. One species re-emerged as the dominant, and the identities of subdominant and rare species remained constant. Although stochastic processes played an important role, the results of these simulations are inconsistent with NBT, i.e., very small niche differences dictated patterns even when all species obey the same simple physical rules.