I am an ecologist interested in both theoretical community ecology and empirical research on the mechanisms that maintain the diversity of tree species in tropical rainforests. My theoretical work has emphasized — but is not limited to — neutral theory. After my book on the subject appeared in 2001, a number of theoretical ecologists and statistical physicists have developed the theory far beyond the original scope of my book. I continue to collaborate with many of these individuals as the subject advances, exploring how neutral theory applies to diverse topics, including speciation and phylogeny, species-area relationships, relative species abundance, and conservation biology.
My empirical research on tropical forests began in earnest when Robin Foster and I started the first 50 hectare forest dynamics study in the world, on Barro Colorado Island (BCI), Panama. Today there are more than 40 such large-plot studies of forest dynamics around the world, all conducted following the protocols developed as part of establishing the flagship plot on BCI. The network of these plots is managed by the Center for Tropical Forest Science at the Smithsonian Tropical Research Institute. Students and postdoctoral research associates in my laboratory, however, still work mainly on the BCI plot, attempting to test a series of classic and newer hypotheses explaining the maintenance of high tree species diversity in the BCI forest. Currently we are testing three major hypotheses and developing a fourth:
The role of spatial heterogeneity in soil nutrients for coexistence of BCI tree species
We are currently collecting soil cores in a stratified sample across the BCI plot and identifying the species having roots in each core using genetic barcodes (all BCI tree species have been barcoded). We are testing the hypothesis that roots of closely related species will segregate in the rhizosphere and that soils more spatially heterogeneous in nutrients will be partitioned more finely by roots of competing species.
The effect of fungal pathogens on commonness and rarity in BCI tree species
Here, we are testing the hypothesis that rare species are rare because they are either more vulnerable to fungal pathogens (particularly heart- and root-rot fungal pathogens) or because they share more pathogens with other tree species - so rare species have fewer "safe sites" (those sites free of infection) in which to establish. We are identifying the heart- and root-rot fungi of BCI tree species and the degree to which they are host specific.
The role of long-lived clones of liana species in enhancing tree diversity
We are testing the hypothesis that larger, older liana genets will be found in areas exhibiting more chronic forest disturbance and that the disturbance caused by liana species not only favors persistence of the liana species but also enhances forest-tree diversity.
Mapping tree populations at the landscape scale
Our final, current, research topic is not, yet, strongly hypothesis-driven, but we are interested in using remote sensing to map tree populations at landscape scales (tens to hundreds of square kilometers) and subsequently using genetic methods to deduce the genealogical relationships within these populations
Where we work
A majority of the field-worked conducted by and/or for the lab occurs on Barro Colorado Island (BCI), Panama, particularly within the Forest Census Plot (aka 50 ha plot) - a study site where over 350,000 trees have been monitored during the previous 25 years.
Our theoretical and laboratory work is conducted by members of the lab within the Dept. of Ecology and Evolutionary Biology at UCLA, where we have all the typical (and some atypical) computer & molecular lab toys.
What we're thinking about
- Tropical forests
- Genetic barcodes
- Mathematical models
- Third-generation DNA sequencing