Kaustuv Roy
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What are the physical and biotic controls on the large scale geographic distribution of species (e.g., along latitude and longitude)? What is the relationship between abundance and geographic range of species? What are the factors that determine the compositions of regional species pools? How do species and communities respond to large scale environmental changes and what are the macroevolutionary consequences of such responses? These and related questions form the focus of our research. Most of our work involves benthic marine species (e.g., gastropods and bivalves) living in shelf environments, and requires the integration of ecological, biogeographical, paleobiological, and molecular data.
The latitudinal gradient in species diversity (i.e., the presence of many more species in tropical regions compared to extra-tropical ones) characterizes most marine and terrestrial biotas, but the factors that control such gradients remain enigmatic. We are currently using marine mollusks living on the eastern Pacific shelf to examine the biogeographic and evolutionary components of this gradient. A comprehensive analysis of geographic and bathymetric distributions of over 3000 species suggests that the distributions of major oceanographic barriers along the eastern Pacific coast play an important role in determining the shape of the diversity gradient. However, a comparative analysis of diversity patterns of gastropods along the western Atlantic and eastern Pacific shelves shows that biogeography is a second order control and not the primary factor behind the high tropical diversity. The distributions of the biogeographic barriers are very different along the two coasts, yet the latitudinal distribution of diversity is remarkably similar. One potential explanation is that differences in evolutionary rates exist between tropical and extra-tropical areas. We are currently testing this hypothesis using data from the fossil record. Initial results suggest that such rate differences do indeed exist; tropical Pacific species seem to have significantly higher speciation and extinction rates compared to extra-tropical ones.
Another question that we are interested in concerns the responses of species and communities to large scale environmental perturbations such as climatic changes during the Pleistocene. The coastal marine terraces in California preserve one of the best late Pleistocene records found anywhere. Over 75% of the shallow water mollusks living along this coast today are preserved in these terraces providing an excellent sample for studying the biotic effects of global change. Data from these terraces reveal that species responded to climatic change by shifting their geographic range boundaries; extinction rates did not rise over background values despite the environmental fluctuations. The patterns are very similar to those observed in terrestrial ecosystems, suggesting that individualistic response of species to environmental change is a common ecological phenomenon.
Other ongoing projects include analyzing the historical components of the longitudinal diversity gradient. More specifically, we are interested in the history of the remarkably high diversity present in the tropical Indo-Pacific. We are using strombid gastropods as a focal group to address this question. This work involves generating a molecular phylogeny for the group and analyzing the paleobiological, biogeographic and macroecological data within that phylogenetic framework. Initial results suggest that for this particular clade, the diversity in the Indo-Pacific is derived from two different sources, a relict Tethyan element and an endemic element.
For a list of Dr. Roy's publications, please visit his lab web page.Kaustuv Roy received his Ph.D. from the University of Chicago, where he completed postdoctoral training. His fieldwork was conducted in Newfoundland, Jamaica, and the western United States.
