Estructuración de un modelo trófico como herramienta de análisis del impacto de la carpa (Cyprinus carpio) en diferentes hábitats del lago de Pátzcuaro”

Abstract

Models represent tools to describe biological systems and to verify and to predict their dynamic processes. In the present study we structured a predator-prey trofic model including producers, primary and secondary consumers using the Ithink/Stella software. The main aim was to evaluate the direct influence from carp (Cyprinus carpio) on different native and introduced fish in Lake Patzcuaro. We created different simulation scenarios to define the environmental influence on fish and prey in favorable and unfavorable conditions. The criteria to select the information in the model structure included: (1) in the case of predators, those species with diets related to the carp’s diet and/or dominant in the ecosystem, and (2) in the case of the food items, those present in all fish diet with the condition that at least they were secondary in two predators. All biological information, from field and laboratory and the analysis of stomach content, was provided by researches from the Facultad de Biología of Universidad Michoacana de San Nicolás de Hidalgo and Centro de Investigaciones Biológicas del Noroeste, S.C. Results showed no direct impact from the carp on the food habits of the other species in Lake Patzcuaro, according to the high abundance of preferential food items. Similarly, no indirect impacts were estimated, including results from the diet composition (there wasn’t any consumption of egg bellowing to other species), carp population size (small densities compared to other fish) and simulation responses. On the other hand, we found an important predator-prey interaction among copepods, cladocerans and Chirostoma species. Two main responses were obtained in their simulation: (a) in the scenario of unfavorable conditions, preferential food decreased promoting a collapse of both predator and prey populations and (b) in the scenario of favorable conditions, higher food availability results on the lack of control from predator to prey and their populations were regulated by the carrying capacity of the ecosystem.