Research: Seed Dispersal
Modeling seed dispersal & its consequences for plant populations and communities
Many hypotheses of plant species diversity involve seed dispersal because it shapes species' distribution patterns at multiple spatial scales and thereby has implications for niche specialization. Seed dispersal, however, can oppose niche specialization, if dispersal is spatially extensive, or reinforce it, if dispersal is spatially clumped. Another focus of my research is understanding which factors determine both large- (between-habitat) and small-scale (within-habitat) distributions of trees and what role contemporary ecological vs. historical evolutionary processes play in creating those distributions.
To address these questions, I have been using comparative phylogenetic analyses of ecological and evolutionary covariation in seed dispersal mode, seed size, and niche specialization of tree species in species-rich mixed Dipterocarp forest in Borneo. With collaborators at the University of Miami and the Center for Tropical Forest Science, I am evaluating whether evolutionary divergences in dispersal mode and seed size of tree species are associated with divergences in their ecological niches and whether interspecific variation in tree species' small-scale distribution could be explained by these three traits (Russo et al. 2007).
I have also been examining the role of seed dispersal in determining species' local distribution in a neotropical nutmeg tree, Virola calophylla (Myristicaceae) in the Peruvian Amazon. Along with collaborators at the University of Illinois, I have developed a mechanistic model of seed dispersal that predicts the spatial distribution pattern of V. calophylla seeds at the forest-stand scale, based on the behavior and movement patterns of its most important dispersal agent, the spider monkey (Ateles paniscus) (Russo et al. 2006).
Our results suggest that the clumped seed dispersal patterns often generated by vertebrate dispersers, such as the spider monkey (Russo & Augspurger 2004), can influence the spatial structuring of some tropical tree populations more so than even strong density-dependent mortality. Understanding how dispersers affect the demography of tropical trees is vitally important, given global losses of vertebrate dispersers from forests due to poaching.
My lab will continue to study the ecological and evolutionary consequences of seed dispersal at multiple spatial and temporal scales. Future research will use our mechanistic model of seed dispersal, demographic models, and population genetic approaches to estimate gene flow by seed dispersal and how it influences the spatial structure of demographic and population genetic variation at different life stages and at different spatial scales.