The Relationship Between Cattle Grazing and Small Mammal Community Structure on South Texas Rangelands

Abstract

Cattle grazing is known to affect ecosystems and potentially alter wildlife abundances and distributions. Small mammals are one group that respond quickly to environmental change and can be used to monitor ecosystems. The goal of this project was to determine how cattle grazing affects small mammal community structure in southern Texas rangeland dominated by tamaulipan thornscrub and coastal sand plain vegetation. My study focused on the East Foundation’s San Antonio Viejo Ranch located in Jim Hogg County, Texas where I conducted an observational study within five relatively large (~61 ha) cattle exclosures that were constructed in 2011. Following nearly ten years of cattle exclusion, this study consisted of sampling small mammals and vegetation in a gradient design to understand the extent of the impact of cattle grazing on the small mammal community. I expected to find that the small mammal community makeup (i.e., species richness, minimum number alive, sex ratios, age ratios) to be unique in at least two locations along the gradient: in the center of the cattle exclosure, and at the farthest point sampled outside of the cattle exclosure, with a possibility of unique makeup along the boundary of the exclosure. I found that minimum number alive, and age ratios were influenced by the presence of cattle while sex ratios and species richness were not. My research provides insight on how cattle influences small mammal communities. By sampling in a gradient manner, I was able to evaluate the impact of the edge effects on this target community which is vital since fragmentation and edge effects at various scales could be negatively impacting wildlife on private ranches. My results suggested that small mammal relative abundance is negatively correlated with cattle grazing. Also, my data supported the presence of an edge effect on age ratios with young individuals being caught most often along the edge of the exclosure. By ensuring small mammal diversity and abundances are not severely negatively impacted, ranch managers can help maintain environmental processes that small mammals are involved in which could increase native forage for cattle.