Local Environmental Variables Predict Fish Species Richness and Composition in Sand Beaches of a Neotropical River

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Abstract
Local and regional species diversity is influenced by historical factors, resource availability, biotic interactions, the presence of resources, and adequate environmental conditions. We evaluated the effects of local environmental variables and spatial structure on fish species richness and composition along sandy beaches of a Neotropical river. The sampling period extended from June to September 2017, encompassing 31 sandy beaches. A comprehensive collection effort yielded 15,627 individuals representing 60 distinct fish species. The PCA indicated that beaches located in the upper part of the river tended to have higher pH, current speed, and shallower depth, while the lower part had greater length, warmer waters, and greater concentration of dissolved oxygen. There was a trend towards lower species richness in the upper part and greater richness in intermediate portions of the Acre River. Multiple regression indicated that only water temperature positively influenced the variation in fish species richness as predicted by the energy‐environment hypothesis. Also, water temperature, concentration of dissolved oxygen, and depth were essential to determine changes in species composition. We found no evidence of spatial autocorrelation. Therefore, local environmental variables, especially the water temperature, are important factors in determining the fish richness and variation in species composition on sandy beaches of the Acre River.

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