Neighborhood models of plant competition have recently proved of considerable use in predicting consequences of local interference to plant population dynamics. In tropical forests, competition is but one of several kinds of local interaction thought to be important; others significant interactions include the effects of "natural enemies" on growth and survivorship of conspecific trees (the "Janzen-Connell effect"), and local pollen limitation of reproductive output in obligately outcrossing species (a form of "Allee effect"). This research will develop general neighborhood models that incorporate competitive interactions as well as Janzen- Connell and Allee-type interactions in tropical tree populations. Empirical analyses and simulation studies will make use of extensive data sets available from 50 hectare forest plots at Barro Colorado Island, Panama and at Pasoh Forest Reserve, Malaysia. An important facet of developing these models will be a focus on dioecious tree species. The fact that female trees produce seed, while male trees do not, provides an unexplored aspect of spatial analyses aimed at elucidating patterns of seed dispersal, and for detecting and measuring Janzen-Connell and Allee-type interactions. It is expected the models will be particular useful in predicting consequences of habitat fragmentation on tropical tree populations. %%% Spatial interactions in tropical forests have received relatively little research attention. A variety of hypothesized mechanisms has been advanced for explaining the maintenance of tree species diversity in tropical forests, including niche partitioning on edaphic gradients, Janzen-Connell effects, "regeneration niche" differences, demographic "storage effects," and size structure effects but these potential mechanisms have generally been modeled in isolation such that effects of interactions have been ignored. Recognition of this shortcoming in previous models may represent the best hope of addressing predicted responses of rainforest trees to habitat fragmentation and other massive anthropogenic changes in the forested tropics.
