Macroinvertebrate communities along the main stem and tributaries of a pre-Alpine river: composition responds to altitude, richness does not

We collected quantitative macroinvertebrate samples and measured environmental and geographical parameters at 13 sites: six along the main stem and seven in tributaries close to the main channel over a 700 m gradient in altitude and 22 km longitudinal distance along the River Kokra in the Slovenian Alps. Our objectives were 1) to compare longitudinal patterns in richness and community composition between main stem and tributary sites, and 2) to determine the relative importance of the replacement and richness difference component for overall beta diversity and of environmental versus spatial distance on beta diversity among main stem and tributary sites.