The relative influences of exotic species and environmental factors on an Iberian native fish community

The contribution of biotic (mainly exotic species' abundance) and environmental factors to spatial variation in native (mostly endemic) fish communities in an Iberian river basin was studied. Total variation in native community composition was partitioned into four independent components-variation accounted for uniquely by environmental variables (24.4%); variation uniquely accounted for by biotic variables (12.4%); variation explained by both environmental and biotic variables (9.2%); and unexplained (54%). Of the 22 variables initially considered, only sampling location, substrate heterogeneity, and macrobenthos abundance were chosen as good predictors of variation. Exotic fish had a significant influence on native community variation after accounting for the effects of environmental influences.