Coexistence of plant species with similar niches

In the context of a simple mathematical model, we derive several mechanisms whereby plant species can coexist in a community without differing in their trophic niches (their relations with habitats, resources and exploiters). The model is based on the dynamics of species turnover in microsites, and incorporates localized competition, non-uniform seed dispersal and aspects of spatiotemporal environmental heterogeneity. These factors, which are not included in most standard competition models, allow stable coexistence of trophically equivalent species due to: (a) Differences in life-history 'strategy'. (b) Input of seeds from neaby habitats (spatial Mass Effect). (c) Differences in demographic responses to environmental fluctuations (temporal Mass Effect). (d) Turnover in species composition between different habitat patches. Quantitative descriptive studies are presented, demonstrating the occurrence of vegetation patterns predicted on the basis of the hypothesized mechanisms. We also review previously proposed mechanisms that would allow trophically equivalent species to coexist, and explore the theoretical and methodological implications of recognizing coexistence mechanisms independent of trophic niche differentiation. In particular, we propose that these mechanisms contribute to the dissimilarity of within-community replicate samples and the maintenance of many rare species in plant communities.