BIODIVERSITY ~ PLANT-HERBIVORE INTERACTIONS

Research in my laboratory explores the abundance and number of species of both plants and animals found in different environments around the world. We primarily do field studies of the factors controlling plant and animal abundance and the number of species found in a particular area. We also work on the conservation of endangered species.

One principal area of my research is studying interactions between plants and animals that eat plants, or herbivores. This work has identified potential prime regions of large mammal species diversity across the globe and helped understand why grazing may be beneficial to the maintenance of biodiversity in productive areas but detrimental in areas with poor, dry soils. We do intensive field studies at sites in North America, including the Rocky Mountain West (Utah and Colorado) and the Great Plains (Kansas and Minnesota), and international sites in the Netherlands and South Africa. These studies set up experimental fences to keep out either large grazers like cows or bison or large grazers and smaller grazers like rabbits. We measure changes in the types and numbers of plant species inside these fences as well as changes in plant production, root production, and soil nutrients. We then compare these changes across the different environments to understand why some areas have many herbivores that eat most of the plant production, while others have relatively few species that have little impact upon vegetation.

Another major area of interest is determining how species of different body size coexist when they compete for the same resources. So far we have developed a mathematical theory to predict the number species that might coexist under different conditions. This work uses an idea from chaos theory - the notion that nature has a fractal geometry, rather than the classical geometry of lines, planes and volumes. Using fractal geometry, we can incorporate information about the distribution of resources and habitats in space, along with the scale of observation and the size of the organism studied, into our predictions. We have tested these predictions in one study of leafhoppers living on prairie grasses, and plan new work in South Africa on dung beetles. This work has broad implications for the conservation of biodiversity, especially the calculation of acceptable levels of habitat fragmentation to conserve species.

The third major area of my research is field studies to help recover a threatened mammal species, the Utah prairie dog, in southwestern Utah. Our work helps prescribe grazing strategies and revegetation plans to form new prairie dog habitat and therefore establish new populations of prairie dogs.

Every year, 3-6 undergraduates work together with graduate students and professional technicians on these projects, either as field assistants or in the lab helping with chemical analyses of plant material. Many opportunities exist for undergraduate research projects. In recent years, students have explored many different topics, including effects of fire on mutualism between ants and aphids, effects of nitrogen pollution on freshwater pond organisms, effects of ant mounds on soil nutrients and vegetation, and the effects of drought on species-poor versus species-rich plant communities.