Influence of Precipitation on Pronghorn Demography in Texas

Abstract

: Ungulate populations in desert environments are thought to be regulated by precipitation. Pronghorn (Antilocapra americana) populations in Trans‐Pecos, Texas, USA, experienced a 70% decline between 1977 and 2001. The causative factors associated with the decline are unknown but appear to be related to drought. We evaluated the relationships between pronghorn abundance and productivity and precipitation (i.e., raw precipitation, Palmer Drought indices) for the Trans‐Pecos district of Texas from 1977 to 2004. Pronghorn productivity (range = 305‐4,407) and abundance (range = 5,061‐17,266) showed high variability. Precipitation was also highly variable, ranging from 18 cm to 57 cm. Pronghorn abundance was positively influenced by precipitation indices (R = 0.790, P < 0.001). The relationship between fawn production and raw precipitation (R = 0.869, P < 0.001) suggested that fawn production may be more closely related to immediate moisture conditions, whereas pronghorn abundance was more influenced by long‐term population trends. Management plans for pronghorn populations in more arid regions should include drought contingencies including reduced stocking rates and harvest quotas.

Effects of climate change on long‐term population growth of pronghorn in an arid environment

“…Had we only tested annual precipitation and temperature covariates in our models, and not incorporated reproductive seasonal climate covariates, we would not have found significant relationships with k. In contrast, other pronghorn studies in the Southwest found prolonged or severe drought (measured annually) related to increased mortality of adults and juveniles (Bright and Hervert 2005). Simpson et al (2007) found a positive relationship between long-term precipitation trends and pronghorn abundance, and short-term rainfall and fawn survival.…”

“…Such climatic changes can alter hydrologic, nutrient, and carbon cycles, changing the availability of water, energy, and nutrients, and thereby altering the forage base for animals (Prato 2009). Previously, such effects have been demonstrated with populations of desert bighorn sheep (Ovis canadensis) and pronghorn in the Southwest , Simpson et al 2007, McKinney et al 2008, Marshal et al 2009). …”

An Assessment of Habitat Suitability for Pronghorn Populations of the Central Valley Region of California

“…A study of the influence of precipitation on pronghorn demography in Texas was done by Simpson et al (2007). The authors asserted that pronghorn populations in the southwestern US appear to be regulated more by density-independent factors than density dependent factors.…”

“…Thus the goal of this study was to evaluate the relationship between precipitation and pronghorn demography in Trans-Pecos, Texas. Within the study area pronghorn habitat was characterized by open, low-rolling grasslands or shrub steppes and much of the rangelands were used for agricultural purposes (Simpson, et al 2007). Results of the study indicated that, based on the relationship between pronghorn abundance and precipitation measures, the Trans-Pecos pronghorn population appeared to be closely related to long-term moisture conditions and that the high variation in precipitation characteristic of the area indicated that pronghorn demographics were more susceptible to drought conditions than other pronghorn populations in the US (Simpson, et al 2007).…”

“…Within the study area pronghorn habitat was characterized by open, low-rolling grasslands or shrub steppes and much of the rangelands were used for agricultural purposes (Simpson, et al 2007). Results of the study indicated that, based on the relationship between pronghorn abundance and precipitation measures, the Trans-Pecos pronghorn population appeared to be closely related to long-term moisture conditions and that the high variation in precipitation characteristic of the area indicated that pronghorn demographics were more susceptible to drought conditions than other pronghorn populations in the US (Simpson, et al 2007). These results suggested that long-term and shortterm drought affect pronghorn populations and fawn production and precipitation levels may be more of a limiting factor in more extreme reaches of pronghorn ranges than in more moderate ranges.…”