Effects of bison trampling on stream macroinvertebrate community structureon Antelope Island, Utah

I quantified hydrologic features and macroinvertebrate distribution, abunda nce, and community structure for paired areas with and without bison trampl ing (crossings) in each of eight streams on Antelope Island, Utah. Percent cover of macro vegetation was significantly lower, while the percentage of sand and mud was significantly higher, in samples from trampled areas. Tota l species richness and number of unique taxa did not differ between trample d and untrampled stream sections, but mean sample richness, diversity, and evenness were all significantly greater in untrampled samples. Of twenty ta xa common enough to analyze individually, nine did not differ significantly with the presence of native ungulates, one was more common in trampled are as, four were more common in untrampled areas, and six had significant inte ractions between trampling and specific stream. Percent composition of vege tation was a significant covariate for the population density of four taxa and fine sand and mud sediments significantly covaried with seven taxa. A n on-parametric multivariate test showed that untrampled macroinvertebrate co mmunities differed significantly from trampled ones. A multivariate ordinat ion determined that the environmental variables of percent cover of vegetat ion, and amounts of sand-mud and pebble sediments, were significantly corre lated with the difference between trampled and untrampled areas, as were a snail (Physella sp.), an amphipod (Hyalella azteca), a mayfly (Baetis trica udatus), and chironomid midges.