On the role of microenvironmental heterogeneity in the ecology and diversification of neotropical rain-forest palms (Arecaceae)

Microenvironmental heterogeneity is important in the ecology and diversification of the rich palm flora that inhabits neotropital rain forests. At small-0.1-10(2) m-scales, neotropical rain forests exhibit high heterogeneity in numerous environmental factors: canopy conditions, conspecifics, other plants, litter, soil factors, topography, and animal mutualists and pests. These aspects of microenvironmental heterogeneity affect the performance and the small-scale distribution of palms in numerous ways, often affecting different species differently. Notably, even subtle environmental variation can be of crucial ecological importance. Microenvironmental heterogeneity promotes the local coexistence of palm species by niche differences among the species and probably also by mass effects and negative density dependence. Sympatric species of the same growth form often differ in terms of light requirements, edaphic-topographic preferences, and possibly also in seed-dispersal patterns, whereas mass effects are likely to account for the local occurrence of a share of the rare species. Density dependence seems to be frequent among large-seeded palms, but its importance needs to be assessed. Microenvironmental heterogeneity is proposed to be an important diversity-generating factor in the neotropical palm flora through the process of parapatric speciation. This hypothesis is based on the observation that, in species-rich palm genera and species complexes, sympatric species or morphs often differ in edaphic-topographic preferences or in characteristics that confer differing light requirements and in traits that favor reproductive isolation.