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) 542-6145


My research uses phylogenetic methods to address questions in ecology and evolutionary biology. My primary interest is biodiversity at broad evolutionary and spatial scales, a topic  I have explored in a variety of study systems.  Below I detail some of the recurring themes of my work.

The Evolutionary Ecology of Amphibians and Reptiles

Most of my research before coming to the Odum School of Ecology 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 also 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 massive.

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 sexual size dimorphisms.  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, the evolution of endosulfin resistance in North American frogs and the evolution of phenotypic plasticity in more than two dozen species of North American ranid, bufonid, and hylid frogs.  I am also leading a collaborative project that considers parallel patterns of adaptive evolution the turtle families Emydidae and Geoemydidae.


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 empirical relationship between phylogenetic signal and evolutionary rate of mammalian traits and the implication of these patterns for models of trait evolution, and (3)  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 amphibian 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 amphibian, 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.

The Macrecology of Infectious Disease

Another recent interest of mine is large scale patterns of disease biodiversity. Many basic questions of wide interest remain to be answered. For example, so far there have only been a handful of studies of the factors that drive patterns of parasite community similarity in wild host species, and the broad comparative studies (i.e., studies of parasites in general rather than a particular group such as helminths or rabies viruses) published to date have focused on either carnivores or primates. One of my current projects is on the effects of phylogeny, range overlap, and ecological similarity on patterns of parasite sharing among wild ungulate species. This study also considers for the first time the effects of sampling bias on apparent patterns of parasite overlap among hosts (i.e., are pairs of well-studied hosts more likely to have known shared parasites than poorly studied hosts), and the degree to which trophic links allow ungulate parasites to spread from ungulates to carnivore hosts. This study is part of the ongoing work associated with a jointly NSF/ NIH/ USDA funded research coordination network focused on the macroecology of infectious disease that I am currently leading. You can read more about our work here.