Found in the headwaters of the Comal and San Marcos River, the fountain darter (Etheostoma fonticola) is on average three-centimeter length fish that feeds upon small invertebrates. Considered endangered by the United States and the International Union for Conservation of Nature (IUCN) The darter has been controversial due to its location in the Edwards Aquifer in south-central Texas, which is recognized worldwide for its aquatic species of flora and fauna, many of which are endangered or threatened like the fountain darter. The Edwards aquifer is also the sole water source supporting the industrial, agricultural, municipal, and recreational needs of nearly 2 million people. Because the darter generally poor competitor and is the first species affected by habitat disruption, the endangered fountain darter has been a focal point for controversies involving the endangered species act, state of Texas groundwater law, and private property rights. We developed an age-structured population matrix model for the fountain darter, calibrated the model within the constraints of published parameter estimates. We then integrated the available synthetic estrogen contamination data of fathead minnow (Pimephales promelas) into the model. We finally used the model to project population dynamics under scenarios of increased synthetic estrogen contaminations.
Results/Conclusions
Population projections indicated that a decrease in population growth due to increased synthetic estrogen concentrations were seen at a maximum of 1.0 ng/l. At the 1.0 ng/l concentration, the population growth rate was 1.013, which is within .5% of the original control growth rate. At higher concentrations, the population did not survive through its full life cycle. In order to test the chosen parameters, the elasticity of the population matrix was found. We found a higher elasticity on the later life stages (juvenile and adult), with the highest elasticity being 2.989*10-4 on the 1.0 ng/l rebound P4 parameter. With all P4 variables either 1 or close to 1, a decrease in those probabilities could drastically reduce overall population growth rates.