Current debate in community ecology focuses on two competing theories for species coexistence in diverse communities: dispersal vs. niche assembly. Dispersal theory emphasizes the role of chance colonization and dispersal limitation whereas niche theory emphasizes species differences in requirements for potentially limiting resources. Plant species distribution patterns have frequently been found to correlate with soil conditions indicating niche assembly processes are important in shaping plant communities. My research links patterns of palm species and soil nutrient distributions with the processes generating palm-soil associations in the lower montane forests of the Fortuna Forest Reserve in western Panama. Recent experimental studies suggest three mechanisms by which plant-soil associations may occur 1) through trade-offs in biomass allocation to below-ground resource acquisition, 2) through differences in resource use efficiency of limiting nutrients, and/or 3) differential investment in defense against herbivores.
Results/Conclusions

Understory palm communities were non-randomly distributed among forests differing in soil nutrient availability. Palm – soil associations were strongly correlated with base cations and nitrogen availability.  Using an experimental approach, I examined the potential of the three aforementioned mechanisms in generating palm-soil associations over soil nutrient gradients in Panama. To assess species differences in allocation to resource acquisition and use, I transplanted seedlings to control and herbivore exclosure gardens in five sites differing in nutrient availability. Species differed in growth rates over 18-months across the sites indicating species specific growth responses with nutrient availability. Transplant experiments indicated that species-specific feedbacks between nutrient availability, physiological response, and the effects of herbivory may be involved in determining growth rates and, thus, the observed palm-soil associations ultimately facilitating the co-existence of a high number of closely related species.