COS 2-2
Immigration and the maintenance of tree diversity in a tropical forest
Most efforts to explain what maintains species diversity in tropical forests have focused on niche-based stabilizing mechanisms, but diversity can also be maintained by immigration at small spatial scales. We conduct three independent quantitative tests of the hypothesis that tree diversity of a 50 ha forest plot in central Panama is maintained primarily by immigration from the surrounding region. We begin with four pieces of empirical data: tree density; mean tree dispersal distance; and area (2500 km2) and species richness of the surrounding region. These four pieces of data in conjunction with mechanistic dispersal models lead to predictions about diversity at the 50 ha scale.
Results/Conclusions
We find that species richness, evenness, and temporal turnover in the 50 ha plot can be predicted with rough accuracy. These results support the hypothesis that immigration is the primary plot-scale diversity-maintenance mechanism. This effectively shifts the question of what maintains diversity onto the regional or biogeographic scale. Our results lead us to the conclusion that a better understanding of tropical forest biodiversity is likely to come from a reduced emphasis on small-scale niche-based stabilizing mechanisms and a greater emphasis on dispersal, beta diversity and long-term, large-scale dynamics.