Our laboratory conducts all three major types of ecological research: descriptive field studies, field and laboratory experiments and modeling. Regardless of the approach, all research in the lab is “question-driven” (i.e., we test specific hypotheses even in descriptive studies). In general, we conduct long-term field studies to understand the dynamics of natural systems and to provide information for the scientific management of these systems. Typically, field studies suggest potential mechanisms for observed processes that are tested experimentally, both in the field and laboratory. At heart, I am an experimentalist, because I believe that experiments yield the most rigorous insights into ecological phenomena. Finally, we attempt to build predictive models for the systems that we study. I am not a big math jock so most of these studies are done in collaboration with modelers or with my graduate students. Conceptually, the lab's focus is linking individual behavior (e.g., habitat selection) to population-level phenomena using fitness correlates such as energy intake/individual growth. A second focus involves the relationship between interspecific-interactions, environmental variation, and patterns of assemblage structure. A final focus of the lab is quantifying the effects of invasive species on native fishes.

Trout have been stocked in streams for sport fishing for decades. Nonetheless, little is known about the impact of this practice on native fishes, especially in North America. We are utilizing a combination of field and lab experiments to determine whether stocked rainbow trout (Oncorhynchus mykiss) affect microhabitat use, foraging success or density of native non-game fishes in North Georgia streams. Our design for the field experiment involves introducing trout using a BACI approach, and we hope to replicate this experiment in two different drainages (Little Tennessee and Etowah). The objective of the laboratory experiment is to evaluate the effects of rainbow trout on microhabitat use, foraging success and social interactions of a common native fish, warpaint shiner (Luxilus coccogenis). We are conducting this experiment in an artificial stream in our laboratory at UGA. Funding for this project comes from the Georgia DNR and Warnell School of Forest Resources.

Perhaps the biggest problems affecting aquatic ecosystems today is increasing sediment loads. In these projects, we are examining the effects of turbidity on: reactive distance, capture success and ultimately optimal habitat use by several water-column fishes (rosyside dace Clinostomus funduloides, river chub Nocomis micropogon, bluehead chub Nocomis leptocephalus), and will probably conduct future studies on an invasive species (yellowfin shiner, Notropis lutipinnis) and blackbanded darter (Percina nigrofasciata). We would like to use these data to build a model that will predict population-level effects of turbidity changes on these species. Experiments are being conducted in our artificial stream systems at UGA and in the laboratory of Mark Fairbrass at Georgia Military College. Funding for this project comes from NSF, EPA and the Warnell School of Forest Resources.An example of a river chub foraging in clear water, one prey is released every minute, four captures are shown. These mpegs are three minutes long and take a while to download, I would only attempt it if you have a high-speed connection (DSL, cable, T1, etc.) Here, a river chub is foraging in water with low turbidity, notice the difference in position of the fish (it holds at the front of the tank) and how prey are captured (the fish turns and captures prey that have passed, rather than capturing them from straight ahead).

We have developed two general models for predicting habitat use in stream fishes both based on energy maximization principles. The model for water-column fishes uses prey-capture success data to predict focal-point velocities that maximize energy intake for water-column feeders (see Grossman, G.D., Rincon, P. A., Farr, M.D., and R. E. Ratajczak. 2002. A new optimal foraging model predicts habitat use by drift-feeding stream minnows. Ecol. Freshwat. Fish 11:2-10). Similarly, our model for benthic feeders predicts that the patchy distribution of prey will be the dominant factor influencing patch-choice in these species (see Petty, T. and G. D. Grossman. 1996. Patch selection by mottled sculpin (Pisces: Cottidae) in a southern Appalachian stream. Freshwat. Biol. 35: 261-276. Thompson, A. R., Petty, J. T. and G. D. Grossman. 2001. Multi-scale effects of resource patchiness on foraging behaviour and habitat use by longnose dace, Rhinichthys cataractae. Freshwat. Biol.46: 145-161. Petty, T. and G. D. Grossman. 2004. Restricted movement by mottled sculpin (Pisces: cottidae) in a southern Appalachian stream. Freshwat. Biol. 49:631-645). We are continuing tests of these models using new species resident to the southern Appalachian streams. Funding for this project comes from USDA Forest Service and the Warnell School of Forest Resources.

We have been conducting long-term fish population censuses in three 100m sites for the past 13 years (3-4X mean generation time of most species) and collecting environmental data from the same sites. During this period, the drainage has experienced extensive environmental variation including high water years and a four-year drought. We will examine patterns in both assemblage structure and examine correlations between assemblage structure, abundance/recruitment of individual species, and environmental parameters (flow variation, depth, substratum composition, etc.). Results from a similar analysis can be found in Funding for this project comes from NSF and the Warnell School of Forest Resources.