Coexistence of the Myristicaceae in an Amazonian rain forest
Mechanisms that have been proposed to explain species coexistence among species of tropical rain forest trees include niche partitioning of the abiotic environment, the positive and negative effects of local neighbours on reproductive success, and the impact of stochastic events and neutral demographic processes. These were investigated using 16 species of a common tree family (the Myristicaceae) on a large forest dynamics plot in Yasuni National Park in Western Amazonia using analytical methods that accounted for spatial autocorrelation in mortality, and habitat and individual stem distribution. Species groups were differentiated with respect to topography and light availability, but short-term demographic responses to topographic variation did not account for species' distributions. There was a negative relationship between established tree abundance and seedling survival across species, and individual seedling survival was strongly negatively influenced by the presence of conspecific and confamilial seedlings. Spatial autocorrelation of mortality was strong at small spatial scales but limited in its extent. There was spatiotemporal variation in both seedling recruitment and seed output. Reproductive success was determined largely by the availability of resources, but estimates of local male density also limited fruit production. I conclude that species coexistence is promoted by both niche assembly and dispersal assembly mechanisms for my study taxa. Niche differentiation permits functional groups of species to coexist. Strong negative density dependent effects restrict the potential for individual species to exclude others, and variation in seed output, dispersal and recruitment allow many rare species to persist by limiting competitive interactions.