Impacts of cattle grazing on small-rodent communities: an experimental case study

Abstract

We used experimental cattle ungrazed and grazed sites to evaluate what impact different intensities of cattle grazing have on deer mice ( Peromyscus maniculatus (Wagner, 1845)) and meadow voles ( Microtus pennsylvanicus (Ord, 1815)). Live-trapping of these small rodents was conducted on paired treatment plots (grazed and ungrazed) at Sheep River Provincial Park in southwestern Alberta, Canada. Before grazing started, both rodent species were equally abundant in either grazed or ungrazed sites. Introduction of grazing resulted in strong but differing responses by both rodent species. Deer mice had higher population density (measured as individual animals trapped) in the grazed than in ungrazed plots, but their body mass was negatively correlated with increasing grazing pressure. Meadow voles were more heavily affected by grazing, as a strong avoidance of cattle-grazed plots was observed already at low grazing intensity. In addition, cattle grazing had noticeable effects, impacting the survival, sex and age ratios, and the ectoparasite prevalence of these two rodent populations. We conclude that there are diverse and different levels of impact of cattle grazing on those two rodents, leading to much more complex species interactions than previously thought. We suggest that the presence or absence, density, and body condition of small mammals could be used as a tool for ecosystem health assessment.