Research Interests
| Effects of herbivores on plant growth and physiology; Effects of nitrogen availability on herbivore damage and plant responses to herbivore damage |
Goals: Understand the physiological basis for growth responses to herbivore damage; understand how nitrogen availability affects amounts and distributions of herbivore damage, and the consequence to plant growth and development
| Physiological and Ecological Mechanisms Determining Plant Species Composition on Desert Islands (Collaboration with Dr. Wendy B. Anderson at Drury University) |
Goals: Our purpose is to investigate what determines plant species composition on 14 islands, 7 of which receive significant inputs of seabird guano (bird islands), 6 of which receive virtually no inputs of seabird guano (nonbird islands), and 1 which has areas with and without seabird guano input. Extreme differences in plant species composition, diversity, and biomass between bird and nonbird islands have led us to ask a number of physiological and ecological questions regarding species’ tolerance to bird and nonbird island soils and competitive interactions between dominant plants on bird and nonbird islands using a series of field and greenhouse experiments.
We have developed a conceptual model that predicts that species growing on bird islands do not exist on nonbird islands either because the saline and low nutrient conditions of nonbird island soils limit their growth and reproduction, or because they cannot grow fast enough to reproduce when in competition with nonbird island species. On the other hand, species that normally grow on nonbird islands cannot persist on bird islands either because the pH or ammonium levels of bird island soils limit their growth and reproduction, or because they are out-competed by the bird island species that grow rapidly in these nutrient rich soils. Because growth and reproduction of all species on these islands are limited to rare and usually short pulses of rain, our model also predicts that interspecific competition during pulses may slow growth of non-local species to an extent that reproduction cannot occur before drought-induced death.
Pictures: Islands, cardon, plants, whale
| Overstory Leaf Developmental Patterns in Ozark Forests and Relationship to Plant and Animal Diversity and Productivity |
Goals: I will test the general hypothesis that seasonal overstory leaf developmental patterns (initiation, expansion, senescence) regulate plant susceptibility to herbivory, understory plant development, and habitat invasibility and suitability for mammals and arthropods. If the hypothesis is correct, overstory leaf development could be used as a predictive variable in forests throughout the Ozarks – and potentially forests in general.
Pictures: Measuring leaf level gas exchange
