Invasion of an Amazonian cichlid in the Upper Paraná River: facilitation by dams and decline of a phylogenetically related species

Biological invasions and damming are currently considered the main threats to aquatic biota. This is aggravated by the facilitative effect of damming on dispersal and establishment of non-native species. In this study, the invasion process by Geophagus proximus, an Amazonian Cichlid fish, was examined in different environments of the Upper Paraná River floodplain and Itaipu Reservoir. The effect of sediment retention prompted by damming (increasing water transparency) in the invasion process was investigated, in addition to the possible effects on the phylogenetically related Satanoperca pappaterra. The invasion process of G. proximus began in upstream reservoirs (source of propagules), then this species occupied the floodplain and later dispersed into the Itaipu Reservoir, being most successful (greater abundances) in environments with high water transparency (most above 200 cm). Increased abundances of the invasive species coincide with declined abundances of S. pappaterra. Diet overlap between these species was high, but apparently related to their omnivorous–detritivorous habits. Reproductive strategies were also similar. Therefore, it appears that the main factor that favored the invasive species was the increased transparency resulted from river damming, and that some interaction with S. pappaterra may be occurring.