The impact of low-head dams on fish species richness in Wisconsin, USA

Communities that live in linear systems such as streams or riparian zones may beparticularly sensitive to changes in habitat connectivity. I examined the relationship betweenenvironmental variables, the number of low-head dams downstream of each reach, and fishspecies richness in first-order streams in Wisconsin, USA. The analysis was based on anextensive database of 13 628 localities and similar to 180 000 individual collection records. The environmental variables included climate, elevation, distance from nearest town, and networkspecificmeasures such as link number (the number of first-order tributaries upstream of thecurrent reach), downstream link number, stream order, and fractal dimension. The link number ofthe downstream reach was the strongest broad-scale correlate of fish species richness in firstorderstreams. Path analysis of a simple directed graph suggested that, although downstreamdams have a significant effect on fish species richness, this effect is small by comparison to theinfluence of water quantity and summer maximum temperatures. From a managementperspective, the results imply that modifications of water volume and temperature are greaterthreats to fish communities than the decrease in connectivity that results from low-head dams. http://dx.doi.org/10.1890/03-530