Effects of Bison Trampling on Stream Macroinvertebrate Community Structure on Antelope Island, Utah

ABSTRACT

I quantified hydrologic features and macroinvertebrate distribution, abundance, and community structure for paired areas with and without bison trampling (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. Total species richness and number of unique taxa did not differ between trampled and untrampled stream sections, but mean sample richness, diversity, and evenness were all significantly greater in untrampled samples. Of twenty taxa common enough to analyze individually, nine did not differ significantly with the presence of native ungulates, one was more common in trampled areas, four were more common in untrampled areas, and six had significant interactions between trampling and specific stream. Percent composition of vegetation was a significant covariate for the population density of four taxa and fine sand and mud sediments significantly correlated with seven taxa. A non-parametric multivariate test showed that untrampled macroinvertebrate communities differed significantly from trampled ones. A multivariate ordination determined that the environmental variables of percent cover of vegetation, and amounts of sand-mud and pebble sediments, were significantly correlated with the difference between trampled and untrampled areas, as were a snail (Physella sp.), an amphipod (Hyalella azteca), a mayfly (Baetis tricaudatus), and chironomid midges.