INTRODUCTIONRegression Analysis of Fresh-water Gastropods Distribution Along the San Marcos River Existing State of Knowledge Most invasion gastropods were introduced by humans in aquarium trade Snails are an intermediate host for liver fluke parasite which is fatal to small native fish
How do snails feed? breed? respire? move? Do these aspects determine where the snail resides in the river, and to how much effect? What significant do the invasive species pose on the native species of the ecosystem? Hypothesis There will be no difference in snail abundances among different flow regimes, substrate type/size, and/or depth.
Materials and Methods Location San Marcos River at the falls of Spring Lake near Salt Grass When 3 separate days in March From 11am-4pm
Regression analysis: analyzing several variables, with a focus on the relationship between the dependent (number of snails and an independent variable (depth, current, substrate size)
RESULTS Fig. 1. Regression analysis, number of snails present as a function of water depth
Fig. 2. Regression analysis, number of snails present as a function of water current
Fig. 3. Regression analysis, number of snails present as a function of substrate size
Fig. 4. Regression analysis of all three variables compared.
Fig. 4. Number of snails present in areas with and without vegetation. Note, only 14 of the 35 sites had vegetation.
DISCUSSION Hypothesis: There will be no difference in snail abundances among different flow regimes, substrate type/size, and/or depth. Compared Results Found in abundance by Kimmel, and Diaz and Alexander. Grantham showed results that support rams-horn have a preference for macrophytes