Modelling self-design of the aquatic community in a newly created freshwater wetland

Abstract

A dynamic simulation model was constructed to predict the natural development of a fish community in a recently constructed, freshwater marsh in the midwestern USA, and to determine which forces are significant in shaping the self-design trajectory of the fish community. The model allowed immigration of five species of fishes from a nearby river into the constructed wetland system and allowed them to interact with each other as well as with the other biotic components of the wetland. Imported fishes included Micropterus salmoides, Lepomis macrochirus, Lepomis cyanellus, Cyprinus carpio and Ameirus natalis. These species were chosen because each is common in the nearby river and because each possesses physiological characteristics allowing survival in typical marsh conditions. Each species population was divided into three distinct ontogenetic stages and were graduated into the next ontogenetic stage as the normal consequence of growth. Modelled interactions included intra and interspecific competition; predation; feeding; reproduction; fish effects on system abiotic components (e.g., bioturbation) and mortality. The fish community underwent several major changes in structure during the first 4 years of its simulated existence, before establishing a stable structure. Under environmental conditions prevailing in the system, the fish community always evolved toward a stable state with a high-biomass population dominated by Cyprinus carpio and a smaller population of Ameirus natalis. If the effects of suboptimal environmental conditions were removed, then the system always evolved toward a low-biomass state consisting entirely of Micropterus salmoides. The role of chance was also tested and resulted in significant short term modifications to the community structure; however, these changes decreased in magnitude and were insufficient to prevent attainment of either of the two alternate steady states. These results indicate that the fish community in wetlands has a strong self-design trajectory, tending toward almost complete dominance by Cyprinus carpio unless typical wetland environmental conditions were significantly ameliorated.