Species-specific population dynamics and their link to an aquatic food web: A hybrid modeling approach

The Topeka shiner, a small cyprinid fish, is a seminal example of an endangered aquatic species in the Midwestern USA. Populations and their associated critical habitats may experience potential direct and/or indirect effects from anthropogenic activity. However, potential impacts on fish populations from alterations in the food web are difficult to predict because they are based on complex dynamics of food web interactions. In order to simulate Topeka shiner population dynamics under different food-web scenarios, a hybrid modeling approach was developed by linking an aquatic food web model (comprehensive aquatic systems model, CASM(TS)) with a species-specific, individual-based population model (TS-IBM). The CASM(TS) was parameterized and calibrated to represent the waterbody conditions and aquatic species community in a small headwater pool in Iowa, representative of key habitat for the Topeka shiner within its geographical range. In the TS-IBM, life history, growth, and diet are represented and based on data available from the literature for the Topeka shiner and/or surrogate species. The two models are linked by the transfer of daily biomasses of Topeka shiner diet items. We simulated the effects of alterations of the food web on the Topeka shiner populations by systematically reducing the available prey base biomass. Reductions in different food groups had varying impacts on the simulated Topeka shiner populations and were dependent on the species' preference for detritus consumption. Simulations also included predation and identified predator densities to which Topeka shiner populations were vulnerable. The hybrid model provides a platform for the assessment of potential direct and food-web mediated indirect effects of stressors for the purposes of risk assessment, habitat management, and species recovery plans.