Despite decades of investigation, there are few ecological studies on the Amazonian fish fauna that have looked both at the main factors shaping the fish assemblages at a regional scale and used environmental, spatial and historical approaches simultaneously. The current study aimed to measure the relative influence of environmental aspects, spatial distance and historical processes on fish genera assemblages in the upper Amazon basin (Peru and Ecuador). Climate, slope and elevation were used as environmental variables; watercourse was used to represent the spatial distance between sites and phylogenetic relationships were used as a proxy for historical processes. A partial Redundancy Analysis (pRDA) was used to compute the influence of each group of factors (environment, space and historical processes) on the fish genera assemblage. Our analysis indicated historical processes had the greatest influence on fish genera assemblages, followed by spatial distance and environment. Such patterns are most likely due to the extinction processes caused by environmental filters generated by the Andean orogeny and possible speciation in each sub-basin. The results suggest that the use of phylogeny, in addition to environment and space, provides a useful tool with which to assess the drivers responsible for fish assemblages at a regional scale.
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