Abstract

Title:  Do Cattle and Nilgai Compete with White-Tailed Deer for Forage in South Texas?
Author(s): Stacy L. Hines - Caesar Kleberg Wildlife Research Institute, Texas A&M University, Kingsville; Timothy E. Fulbright - Caesar Kleberg Wildlife Research Institute, Texas A&M University, Kingsville; J. Alfonso Ortega-S - Caesar Kleberg Wildlife Research Institute, Texas A&M University, Kingsville; David G. Hewitt - Caesar Kleberg Wildlife Research Institute, Texas A&M University, Kingsville; Thomas W. Boutton - Texas A&M University, College Station
Year: 2014
Abstract: Competition for forage resources between large ungulates and white-tailed deer (Odocoileus virginianus) can be of concern for ranch managers. Stable isotope analysis provides a way to investigate niche partitioning among species. Our objective was to determine if cattle (Bos spp.) and nilgai (Boselaphus tragocamelus) diets overlap with white-tailed deer diets during the peak of autumn growing season in south Texas. Stable isotope analyses of fecal samples reflect the average diet consumed within 2-8 days, and has little interspecific variation. We collected fresh fecal samples at 20 random locations from each species across 6 6,177-acre study sites on East Wildlife Foundation ranches in southern Texas. Total grazing niche is defined as variation within and between species, hence we analyzed carbon (δ13C) and nitrogen (δ15N) isotope signatures using F-tests with grazing niche overlap indicated if P > 0.05. There was a species*study site interaction (P < 0.05); therefore we analyzed each site separately. δ13C was similar among sites (P > 0.05), but δ15N differed between nilgai and deer at one site (P < 0.05). δ13C and δ15N varied between cattle and deer at 5 sites (P < 0.05) indicating no diet overlap, however diet overlap was apparent at one site (P > 0.12). Nilgai compete with deer, while cattle and deer only competed at one study site.

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