Stochastic Recruitment in White-Tailed Deer along an Environmental Gradient

Abstract

Texas encompasses a strong precipitation gradient from arid deserts ( 1,300 mm) in the east. We examined the relationship between fawn recruitment in white-tailed deer (Odocoileus virginianus), as estimated by fall census data, and same-year precipitation along this environmental gradient. Census data for the years 1977-95 were obtained from the Texas Parks and Wildlife Department. Precipitation data covering the same period were obtained from the National Oceanographic and Atmospheric Administration for every official recording station in the state. Data were summarized by 8 precipitation zones, followed by exploratory regression analyses that revealed a changing pattern in recruitment along the precipitation gradient. The best model was a simple linear regression that incorporated the sum of March-July precipitation as the independent variable and recruitment expressed as fawns per 100 does as the dependent variable. In arid western Texas, recruitment was strongly and positively related to March-July precipitation totals. Moving eastward, regression slopes declined as precipitation totals increased. In eastern Texas, regression slopes indicated a negative relationship between recruitment and precipitation. Long-term average recruitment across precipitation zones is negatively correlated with long-term average precipitation. We suggest various causal explanations for these relationships.