Current Research

I am collaborating with Lisa Belden at Virginia Tech to understand the controls on the abundance and distribution of trematode parasites (Echinostoma trivolvis). Amphibians are the second intermediate host of many trematode species, so we are also trying to understand what consequences parasitism might have on amphibian populations.

Current Student Projects

Joseph Pruitt, Matt Nichols, and Lindsey Poole have been working on several projects together:

Do parasite hosts (the snail Helisoma trivolvis) decrease or increase their risk of infection by trematodes when they consume trematode eggs?

How does eutrophication (nutrient pollution) affect the transmission of trematode parasites to/from the first intermediate host (the snail Helisoma trivolvis)?

Past Student Projects

Yumi Kidokoro conducted a laboratory experiment where we documented how the behavioral responses of aquatic snails to their predators vary across a resource gradient (follow-up to Wojdak and Luttbeg project described below).

Sara Shakeshaft conducted a field survey of macroinvertebrates in local ponds, and hopes to use biotic and abiotic parameters measured in each pond to help explain variation in invertebrate community composition across the landscape.

Coleman Trexler conducted a mesocosm experiment examining the relative strength of density- and trait-mediated indirect effects of a predator (Belostoma, the giant water bug) across a gradient of predation intensity. Coleman hopes to present his project at the National Council on Undergraduate Research Annual Meeting in Asheville, NC this spring.

Jason Crolley examined the interactions between abiotic (chemical pollutants) and biotic (competition/ predation) stresses on the black worm (Lumbriculus variegatus).

Julie Brooks conducted a mesocosm experiment to determine if more diverse pond communities were more resislient to perturbation from pesticides.

Dissertation research

My dissertation research focused on the relationship between the number and composition of species present in an ecosystem and the resulting properties of that ecosystem.  Theory predicts that having more species present should promote greater rates and temporal stability of ecosystem processes (e.g., primary productivity or nutrient cycling).  Greater rates of ecosystem processes with increasing diversity can result from complementary niches among species or facilitative interactions, while functional redundancy among species can buffer ecosystems from change in much the same way as structural redundancy in an airplane buffers it from catastrophic failure.  These ideas have attracted much attention from scientists and the public alike because global extinction rates of most taxonomic groups are thought to be higher than at any previous time in the earth’s history and because humanity relies on the products of ecosystem function (e.g., timber/agricultural products, hydrological stability, atmospheric gas balance).  

In my dissertation I studied these ideas at a variety of scales in lab and field microcosms using aquatic snails, their algal prey, and their insect predators as a model system.  Some of the exciting results from this research were 1) The number of species of herbivorous snails present in pond microcosms can have strong effects on whole system properties like the biomass of herbivores, aquatic plants, and attached algae, as well as net system primary production and respiration. 2) The presence of predators or nutrient enrichment can alter the effects of species richness and of particular species on ecosystems. 3) Species richness effects on food webs and ecosystems are as strong as top-down (predation) and bottom-up (nutrient enrichment) forces, long thought to be dominant structuring forces in aquatic communities.  My dissertation work is novel in that it is among only a handful of species richness-ecosystem function studies in aquatic systems, with consumer species, or investigating how other factors interact with species richness {in press, Ecological Monographs, 2005}.

Collaborations

I.  Predators can change both the density of their prey and the traits (e.g., behavior, morphology, physiology) of their prey.  If prey become less abundant or less active, predators can indirectly affect other non-prey species because the prey interact less strongly with their resources, competitors, etc (see figure below).  Rarely has anyone established whether predators' effects on prey traits or prey density tend to generate stronger indirect effects.  I collaborated with Barney Luttbeg (at Michigan State University, now at University of California, Davis) to investigate the relative strength of trait-mediated and density-mediated indirect effects across a gradient of resource availability {Oikos 111:592-8, 2005}.

II. I collaborated with Nathan Dorn at Michigan State University (now at Florida International University) to study how the presence of an omnivorous crayfish (Orconectes virilis) alters the community structure of whole ponds recovering from disturbance.  To address this question, we manipulated replicate (n=3 per treatment) whole ponds, and then performed a time series of surveys of various biotic (benthic and planktonic algal biomass, aquatic plant biomass, primary productivity, zooplankton and benthic macroinvertebrate biomass and composition, fish biomass and growth) and abiotic (water clarity, pH, nutrient availability, conductivity) variables.  The presence of just one species had remarkable impacts on the community structure of the replicate ponds - specifically crayfish decreased the abundance of macrophytes and tadpoles, decreased fish reproductive success, altered water clarity and phytoplankton biomass, and changed the balance of respiration and photosynthesis in the ponds {Oecologia 140(1):150-9, 2004}.  Illustration below by Jonathan Hernandez.

III. As a part of two working groups at the National Center for Ecological Analysis and Synthesis I explored existing data from long-term ecological studies of terrestrial plant communities in the U.S. and South Africa.  One project  focused on temporal variability in the relationship between plant diversity and primary productivity.  A second project explores the stability of species composition and production of grasslands near the Ngorongoro Crater in Tanzania, Africa.  A third project explores the generality of terrestrial vegetation response to fire and grazing; can ecological rules defined in one system (North American grasslands) be usefully employed to predict patterns in another (South African savannahs)? {Frontiers in Ecology and the Environment 2(9):483-491, 2004}  While terrestrial plant communities are not a primary research interest of mine, it has been rewarding to contribute to these projects, and to learn some quantitative skills necessary to synthesize multiple large, long-term datasets .

IV. My research advisor (Gary Mittelbach), labmates (Chris Steiner, Nathan Dorn, Tara Darcy-Hall, and Erica Garcia), and I collaborated to study whether density-independent mortality could lead to coexistence of competing species.  Many ecologists have "intuitive" expectations that mortality from disturbances can promote coexistence, even if it does not fall predominately on the competitively superior species.  We conducted a lab experiment with zooplankton as the focal competitor taxa and found no support for such a mechanism of coexistence {Oikos 107:415-421, 2004}. During the course of this experiment we noticed some "competitor" zooplankton species actually seemed to be facilitating each other.  In a follow-up paper we explored our data for evidence of competition and facilitation, and consider what functional implications these interactions have at the community and ecosystem levels {Oikos 110:556-566, 2005}.