Research Interests

Species interactions in salamander assemblages and the food web of headwater streams. The Southeast is the worldwide center of salamander diversity, and within this region, the Southern Appalachians has the highest species density. Here the lungless salamanders of the family Plethodontidae have a wide array of patterns of distribution and species interactions at multiple spatial scales. The ecotone between headwater streams and the forest interior is the site of strong interactions between salamanders of the genus Plethodon that have direct development and live in the forest and other plethodontid salamanders, especially those of the genus Desmognathus, that have aquatic larvae and so require streams for breeding.

I have several arrays of artificial streams and woodland seeps at Mountain Lake Biological Station that have been used by my students and me to test hypotheses about the role of species interactions in determining the local distribution and abundance of salamanders. The streams have also been used to study interactions between salamanders, brook trout, and crayfish (Bill Resetarits and Wendy Palen).

Population Dynamics in Variable Environments. Grants from the NSF and Conservation International have supported a study by Don Church of the metapopulation dynamics of the 18 species of amphibians that breed in a complex of 32 ponds in the George Washington National Forest. Our primary goal is to evaluate the role of movements among populations in the population dynamics at individual ponds. Don completely fenced three breeding ponds and monitored all amphibians that entered and left each pond each day for four years. Seven species were photographed in order to be recognized as individuals upon recapture. I was involved in the fieldwork when possible, but most of my effort is in developing the mark-recapture analysis and individual-based models of several of the species in collaboration with Don ans with Jim Nichols, Bill Kendall, and Larissa Bailey of the USGS. Our work has direct conservation implications because one of the focal species, the Eastern Tiger Salamander (Ambystoma tigrinum), is endangered in Virginia.
Theoretical work on a general model of the interaction between dispersal, iteroparity, and delayed maturity is closely linked to these empirical studies. This study connects with my long-standing interest in the ecological implications of complex life cycles in which a species uses the larval and juvenile stages to exploit different habitats.

The Ecology of Environmental Sex Determination. A small under-story tree at Mountain Lake Biological Station, striped maple (Acer pensylvanicum), can change between being vegetative, male or female between years. These switches can occur at the level of individual meristems, but usually a whole branch and even the entire tree expresses one sex. A fungal disease that is caused by Rytissma punctatum attacks leaves and developing samaras. I have individually tagged about 3000 trees and have been tracking their sex expression, growth, and survival since 1991. The goal of this study is to understand how individual trees respond to their environment by switching sex. I am also developing matrix models for the population dynamics of plants that change sex expression between years. This project has involed collaborations with Miles Silman (Wake Forest), Pat Peroni (Davidson) and Mickael Hood (Virginia).

The Ecology of Forked Fungus Beetles. The forked fungus beetle, Bolitotherus cornutus, lives in small groups on colonies of the wood-rotting fungus Ganoderma applanatum, on hardwood snags and logs. The beetles lay eggs on the fungal brackets, the larvae bore in the sporophore, pupate and eclose in brackets, and adults feed on the surface of brackets and seek shelter in old tunnels or under the bark of snags. Adult males show an allometric relationship between horn size and body size. Previous research by Jeffrey Connor (Michigan State) demonstrated directional selection on horn length because males with larger horns have greater access to females and more inseminations than males with small horns. Mike Whitlock in his doctoral research with Dave McCauley at Mountain Lake showed that the local populations show strong genetic structure suggesting low rates of movements between colonies. I am interested in studying how density-dependent interactions between larvae confined to brackets of different sizes and ages determine the distribution of horn lengths within a colony. Hence this is a study of the ecological basis of sexual selection. I am also interested in developing models linking the dynamics of the resource (fungal brackets) with the dynamics of the beetles.

Community Structure and Land-use History. My wife Becky, a plant community ecologist, and I have recently begun a long-term study of the forest history at Mountain Lake. Our first study with Cristin Conner, an REU in 2002, is testing the hypothesis that browsing by deer and competition by ferns limits the recruitment of seedlings of canopy trees into the understory. This work follows closely on the heels of a similar study by Sarah Swank (Bridgewater) and Jon Kastendiek (James Madison) at the station. They concentrated on cinnamon fern; we are working in nearby areas dominated by New York or hay-scented fern. We are also surveying the distribution of all woody and herbaceous vegetation on the station as well as the species of canopy trees and their age and diameter distribution. We expect this project to involve primarily undergraduate students.