Relationships Between Water Developments and Select Mammals on the U.S. Army Dugway Proving Ground, Utah

Rodent communities comprise a majority of the mammalian diversity within a host of ecosystems and provide a significant portion of the available biomass consumed by higher trophic organisms. Rodents also influence the structure and composition of vegetation communities and contribute to the supply of several ecosystem services. The importance of rodent communities, coupled with increases in anthropogenic modifications to landscapes, creates a need for determining if such modifications affect rodent communities. The construction of artificial water developments for wildlife in the deserts of the western United States is commonplace, but developments have been proposed to have unintentional negative impacts to desert adapted species and communities. To test these negative impact ideas, we employed a BACI and observational design over four summers to determine if water developments influenced rodent abundance. We found no evidence that water developments negatively impacted rodent abundance. Estimates of total rodent abundance for trapping grids that were distant and proximate to water developments under the observational design framework were similar [i.e., overlap of 95% confidence intervals (CIs)] during 87.5% (7 of 8) of trapping sessions. The 95% CIs for rodent abundance at distant and proximate grids _________________________ 1 Co-authors are Eric M. Gese and Steven J. Dempsey; chapter is formatted for Journal of Mammalogy 14 under the BACI design framework overlapped during 75% (3 of 4) of trapping sessions prior to the water manipulation; in all three cases abundance was lower at proximate grids. Following the water manipulation, non-overlap of 95% CIs occurred during 100% (4 of 4) of trapping sessions; rodent abundance estimates were lower at proximate grids in all cases. Rodent abundance appeared to be driven by a combination of spatial (e.g., vegetation structure heterogeneity) and temporal (e.g., variations in seasonal precipitation) factors. Our findings suggested that water developments on our study area did not significantly impact rodent communities. INTRODUCTION Rodent communities comprise a majority of the mammalian diversity within a host of ecosystems (Feldhamer et al. 2007; Jones and Safi 2011; Merritt 2010), provide a significant portion of the available biomass consumed by predators (Andersson and Erlinge 1977; Sieg 1987), and can influence the structure and composition of vegetation communities (Sieg 1987; McMurray et al. 1997). Recent investigations have found that rodent assemblages contribute to the provision of ecosystem services such as groundwater recharge, regulation of soil erosion, regulation of soil productivity potential, soil carbon storage, and forage availability (Martinez-Estevez et al. 2013; Longland and Ostaja 2013). Factors reported to influence such communities included predation (Stapp 1997; Henke and Bryant 1999; Shenbrot 2014), competition (Heske et al. 1994; Stokes et al. 2009; Shenbrot 2014), precipitation and primary productivity (Ernest et al. 2000; Thibault et al. 2010; Shenbrot 2014), vegetation characteristics (Whitford and Steinberger 1989; Hernandez et al. 2005; Thompson and Gese 2013), and both natural and 15 anthropogenic disturbances (Ramirez and Hornocker 1981; Medin and Clary 1989; Kutiel et al. 2000). Of these, anthropogenic disturbances are receiving increasing attention due to their growing pervasiveness on many natural landscapes. Investigations have revealed negative impacts on rodent communities for a host of anthropogenic disturbances, including urbanization (Umetsu and Pardini 2007; Shenko et al. 2012), livestock grazing (Medin et al. 1989), predator removal (Henke and Bryant 1999), and military training activities (Shenko et al. 2012). Conversely, disturbances such as roads and road traffic (Bissonette and Rosa 2009; Rotholz and Mandelik 2013), wind farm construction (de Lucas et al. 2005), and military training activities (Thompson and Gese 2013) have been shown to have benign or positive impacts. The variability of the effects of anthropogenic disturbance on rodent communities suggests a myriad of ecological processes are likely at play, that disturbances may have direct or indirect impacts on communities, and that similar types of disturbances may not impact communities occurring in different areas in the same fashion. Hence, there may be a need to limit inference outside the scope of site-specific investigations and address the role of specific anthropogenic disturbances on rodent communities on a case by case basis, and when possible, incorporate sampling designs that allow studies to go beyond a purely observational nature. One type of anthropogenic modification that has been suggested as a possible disturbance in arid environments is artificial water developments that were constructed to benefit certain wildlife species (hereafter water developments). Free water has been reported as a key limiting factor on individual species and communities (Leopold 1933), especially in arid systems (Rosenstock et al. 1999; 16 Krausman et al. 2006). As a result, the construction and maintenance of water developments in arid regions of the United States is a common practice. The intent of such developments is the addition of free water on a landscape in order to increase populations, influence animal movements, effect distributions of wildlife species, and facilitate livestock grazing (Simpson et al. 2011, Larsen et al. 2012). At the end of the last century, 10 of 11 western USA state wildlife agencies reported ongoing water development programs with combined annual expenditures >$1,000,000 US dollars (Rosenstock et al. 1999), and as of 2013, nearly 7000 water developments had been constructed in the western United States (Larsen et al. 2012). Furthermore, water developments have been utilized as a mitigation technique to offset the impact of military activities (Broyles 1995). Larsen et al. (2012) forecasted that the importance of water developments will increase as a conservation and management tool in the western United States. Though water developments are unique in that they are explicitly constructed to benefit certain targeted species, they also represent a potential disturbance on the landscape. In recent years researchers have posited that water developments may negatively impact communities indirectly, by way of spreading disease, encouraging exotic species, or negatively influencing populations not dependent on free water by way of increased predation or predation risk (Broyles 1995; Rosenstock et al. 2004; DeStefano et al. 2000; Simpson et al. 2011). The notion that the addition of free water on arid landscapes negatively impacts desert adapted species is known as the indirect effect of water hypothesis (Hall et al. 2013). Investigations testing the indirect effect of water 17 hypothesis are rare, especially at the community level. DeStefano et al. (2000) suggested the leporid community was negatively impacted in areas near water developments due to increased presence of mammalian and avian carnivores. Conversely, Cutler and Morrison (1998) found no evidence that water developments affected the relative abundance of rodents or reptiles. Carnivorous mammal and avian species known to regularly prey upon rodents have been documented to regularly visit water developments during the summer months in arid environments (Rosenstock et al. 2004; O’Brien et al. 2006; Hall et al. 2013). To date, no investigations have tested the indirect effect of water hypothesis on rodent communities using either long-term monitoring (i.e., > 2 years) or an experimental/manipulative study design. Whether rodent communities are indirectly affected by water developments may help guide future management decisions for wildlife management agencies, sportsmen groups, and conservation organizations, especially in arid areas where the animal communities are partially comprised of rare or imperiled species, or when rodents comprise the primary food source for rare or imperiled carnivores. The overall objective of our study was to elucidate the indirect effects of water developments on the rodent community in a cold desert system. Specifically, we used both an observational and BACI design to determine 1) whether total abundance of rodents was different near to or away from active water developments, and 2) whether removal of water developments affected the total abundance of rodents.