Influence of niche and neutral processes on fish communities associated with changes in macrophyte rafts along the hydrological cycle

Abstract

Aquatic macrophytes add structural complexity to the environment, which influences fish species. The structure of macrophytes rafts can vary depending on the hydrological cycle and space availability. Thus, the objective of the present study was to evaluate which predictors associated with environmental conditions, composition of macrophyte species and spatial factors can affect fish communities in different hydrological regimes. The study was carried out in oxbow lakes in the Amazon, in the middle Purus River, Amazonas, Brazil. Samples of fish and macrophytes were collected during the flood, receding and drought periods, and environmental variables were measured in all macrophytes rafts. Partial redundancy analysis was applied to quantify the relative contribution of environmental variables, macrophyte composition and spatial factors in the fish community. Our study revealed that environmental conditions and macrophyte species composition, and both spatially structured as well, were the main factors that explained changes in fish composition in floating meadows of oxbow lakes. Corroborating our predictions, the variations in the fish communities were explained mainly by niche-based processes, including environmental conditions and macrophyte species composition as an environmental component, which varied over the hydrological cycle. The spatial component was more important during flooding, environmental conditions during receding, and macrophyte species composition during the drought hydrological regime. However, the shared explanations that indicated a spatially structured environment, both for environmental conditions and for composition of macrophytes, were greater during all hydrological regimes, also supporting our prediction.