Dr. Patrick R. Stephens
Assistant Research Scientist
Odum School of Ecology
140 E. Green St., University of Georgia
Athens, GA 30602
e-mail: prsteph@uga.edu
phone: (706) 542-3971
My research uses phylogenetic methods to address questions that lie at the intersection of ecology and evolutionary biology. The major focuses of my research are (1) the systematics and evolutionary ecology of amphibians and reptiles (particularly emydid turtles), (2) vertebrate biogeography and trait evolution, and (3) niche conservatism and the factors controlling the distribution of species and lineages (particularly the origins of geographic patterns of community structure).
Most of my previous research focused on the evolutionary ecology of amphibians and reptiles, particularly turtles in the family Emydidae. Emydidae includes many well known North American Turtle species, such as the Eastern Box Turtle (Terrapene carolina), the Painted Turtle (Chrysemys picta), and the Pond Slider (Trachemys scripta). It has been an ideal study system for me because the family is geographically very widespread and species in it are ecologically incredibly diverse. It is one of the very few families of vertebrates to include aquatic, terrestrial, and semi-terrestrial species as well as herbivorous, carnivorous, and omnivorous species. It is among the few terrestrial clades to exhibit a "reverse latitudinal diversity gradient," where more species occur in temperate than tropical regions. Some species in the genus Graptemys also exhibit some of the most extreme sexual size dimorphisms known in tetrapods, with adult females that are more than twice as long as adult males and roughly an order of magnitude more masssive.
Topics I have addressed in emydids include the origins of large scale patterns of species richness, the evolution of ecological specialization, the origins of large scale patterns of community structure, and the evolution of sexuals size dimorphims. One theme that runs through much of this work is that niche conservatism and dispersal limitation greatly influence emydid biodiversity at large spatial scales. Other projects in herpetology include the origins of large scale patterns of species richness in hylid frogs and the evolution of endosulfin resistance in North American frogs. Studies planned for the near future include work examining the evolution of phenotypic plasticity in more than two dozen species of North American ranid, bufonid, and hylid frogs.
Here at the Odum school of Ecology, I have been engaged in a number of collaborative studies of global patterns of biodiversity in mammals. Using resources such as published species level mammal supertrees, IUCN data on mammal geographic ranges, and compiled data on mammalian behavioral, morphological, and ecological data in PanTHERIA it is now possible to address key questions in evolutionary ecology at unprecedented scales. Topics that I am currently engaged in include (1) the effects of niche conservatism on the phylogenetic heritability of geographic range distributions in mammals, (2) the factors that affect patterns of parasite community similarity between mammal species, and (3) the the biological correlates of variation in nucleotide substitution rates among major mammal clades, (4) how trait diversity relates to other dimensions of biodiversity such as species richness and phylogenetic diversity.
In the future, using techniques and theoretical approaches developed in mammals, I will broaden this research to encompass other vertebrate groups, particularly amhibian and reptile groups. Supertrees are available or soon will be available for most major vertebrate groups, and species geographic range data are available for the majority of terrestrial vertebrates. The last major hurdle to cross is developing data bases of species trait data before global scale analyses similar to those that are now possible in mammals are feasible in other groups. Basic questions that are ripe to address include (1) whether global patterns of phylogenetic diversity and trait diversity are similar between terrestrial endotherms and ectotherms, (2) whether the historical drivers of modern patterns of species richness are the same in terrestrial amhibian, reptile, and mammal groups, and (3) whether the biological and demographic correlates of threat status among species are similar or dissimilar among various terrestrial vertebrate groups.
