Low Neutral Genetic Diversity in an Isolated Greater Sage Grouse 119

Schulwitz et al.: Low Neutral Genetic Diversity in an Isolated Greater Sage Grouse 119 LOW NEUTRAL GENETIC DIVERSITY IN AN ISOLATED GREATER SAGE GROUSE (CENTROCERCUS UROPHASIANUS) POPULATION IN NORTHWEST WYOMING SARAH SCHULWITZ JEFF A. JOHNSON DEPARTMENT OF BIOLOGICAL SCIENCES AND INSTITUTE OF APPLIED SCIENCES UNIVERSITY OF NORTH TEXAS DENTON BRYAN BEDROSIAN CRAIGHEAD BERINGIA SOUTH KELLY, WY ABSTRACT populations had become isolated and whether it was primarily due to recent habitat fragmentation or more Habitat loss is well recognized as an immediate historic processes. Due to its small population size, threat to biodiversity. Depending on the dispersal continual monitoring of the population is recommended capabilities of the species, increased habitat with the goal of at least maintaining current population fragmentation often results in reduced functional size and, if possible, increasing suitable habitat and connectivity and gene flow followed by population population size to levels recorded in the past. decline and a higher likelihood of eventual extinction. Knowledge of the degree of connectivity between INTRODUCTION populations is therefore crucial for better management of small populations in a changing landscape. A small Habitat degradation and fragmentation due to population of greater sage-grouse (Centrocercus human mediated activities are considered primary urophasianus) exists in northwest Wyoming within the factors contributing to global biodiversity decline (Sala Jackson Hole valley, including Grand Teton National et al. 2000; Fahrig 2003; Baillie 2004). As habitat is lost, Park and the National Elk Refuge. To what degree the populations become increasingly distant from each Jackson population is isolated is not known as natural other leading to reduced gene flow and loss of genetic dispersal barriers in the form of mountains and diversity through drift (Reed 2004; Frankham 2005; anthropogenic habitat fragmentation may limit the Ezard and Travis 2006; see also Johnson et al. 2003, population’s connectivity to adjacent populations. Using 2004; Dixo et al. 2009; Delaney et al. 2010). This pattern 16 microsatellite loci and 300 greater sage-grouse is becoming increasingly pervasive throughout human samples collected throughout Wyoming and southeast inhabited environments with many species possessing Montana, significant population differentiation was isolated populations of various size and associated found to exist among populations. Results indicated that fitness related consequences (Westemeier et al. 1998; the Jackson population was isolated relative to the other Madsen et al. 1999; Blomqvist et al. 2010; Fei et al. sampled populations, including Pinedale, its closest 2011). Isolated or peripheral populations may be more neighboring large population to the south. The one susceptible to environmental and demographic exception was a small population immediately to the stochasticity due to factors limiting their distribution east of Jackson, in which asymmetric dispersal from and other conditions such as minimal gene flow and Jackson into Gros Ventre was detected. Both Jackson small population size (e.g., Peterman et al. 2013). and Gros Ventre populations exhibited significantly Therefore, these populations are of important reduced levels of neutral genetic diversity relative to conservation concern (Channell and Lomolino 2000) other sampled populations. More work is warranted to especially given that many isolated or peripheral determine the timing at which Jackson and Gros Ventre populations often harbor unique genetic diversity Published by Wyoming Scholars Repository, 2015 1 University of Wyoming National Park Service Research Center Annual Report, Vol. 35 [2015], Art. 16 120 (Nielsen et al. 2001). Much work has focused on candidate for protection under the Endangered Species identifying recently isolated populations in an effort to Act with a final decision due by the end of fiscal year help inform management and thereby mitigate potential 2015. fitness consequences that may contribute to local extirpation and ultimately species extinction (Kyle and Recent work investigating connectivity among Strobeck 2002; Segelbacher et al. 2003; Ratkiewicz et sage-grouse populations throughout their entire al. 2012; also see Henle et al. 2004; Prevedello and geographic distribution identified a total of ten distinct Vieira 2010). population-level clusters based on genetic methods (Oyler-McCance et al. 2005). The majority of these Sagebrush-steppe habitat in North America is clusters, however, were explained largely by isolation one example where dramatic land-use changes over the by distance (IBD) suggesting connectivity among the past century have resulted in the isolation and decline of primary core regions (i.e., southeast Oregon, northeast many sagebrush dependent species (Knick et al. 2002, Nevada, southern Idaho and much of Wyoming and 2003; Rowland et al. 2011). The sagebrush biome eastern Montana; Oyler-McCance et al. 2005; see also (Artemesia spp.) was once a dominant habitat type Bush et al. 2011). Several small, isolated populations across much of northwest United States, but has been were also identified, located on the periphery of the recently altered by human-mediated practices including species’ current range in Colorado, Utah, Washington, agriculture, livestock grazing, infrastructure and on the California/Nevada border, some of which had development, energy exploration and extraction for oil reduced genetic diversity compared to populations and gas, invasive species (e.g. cheatgrass, Bromus sampled in the core of the species’ range (Oyler- tectorum), and changes in fire regime (Knick and McCance et al. 2005). Many of these isolated Connelly 2011). Many of these factors have a populations have resulted from recent habitat cumulative effect, resulting in sagebrush habitat fragmentation (i.e. see Schroeder et al. 2004; Oyler- fragmentation, degradation, and loss. Accordingly, McCance et al. 2005). As sagebrush habitat is lost, animals considered sagebrush obligates, including isolated populations will continue to decline in size and Brewer’s sparrow (Spizella breweri), pygmy rabbit lose genetic diversity by genetic drift, further reducing (Brachylagus idahoensis), and pronghorn (Antilocapra population viability and increasing risk of extirpation americana), have responded negatively to habitat (Frankham 2005), a common theme among lekking alteration and fragmentation and are of increasing grouse in general (i.e., extinction vortex; Soule and conservation concern due to decreased abundance Mills 1998). (Baker 1976; Knick and Rotenberry 2002; Rowland et al. 2006). For example, the pygmy rabbit has The primary objective of this study was to experienced a significant decline in population size and assess the degree of isolation and level of genetic was listed as an Endangered Species in 2003 (USFWS diversity of a relatively small sage-grouse population 2003). Likewise, energy development activities have located in the Jackson Hole valley of northwest been shown to displace mule deer (Odocoileus Wyoming (herein referred to the Jackson population). hemionus), and increasing concern exists that the The current Jackson sage-grouse population is estimated removal and disruption of migration corridors for mule to be between 300 and 500 individuals, existing deer and pronghorn may have negative impacts on their primarily on protected federal land (Grand Teton long-term population sustainability (Sawyer et al. 2005, National Park and the National Elk Refuge) with an area 2006). of approximately 9,500 hectares of sagebrush habitat (B. Bedrosian, unpubl. data; see also Garton et al. 2011). To The greater sage-grouse (Centrocercus what degree this population is isolated from surrounding urophasianus, hereafter referred to as sage-grouse) is a sage-grouse populations is not known, but potential sagebrush obligate that has also experienced range-wide dispersal barriers do exist surrounding this population, population decline and contraction and now occupies including forested mountains to the west, east and approximately 56% of its pre-European settlement southeast, the city of Jackson to the south and distribution (Schroeder et al. 2004). Populations of this Yellowstone plateau with more forested high elevation species have become increasingly fragmented and habitat to the north (Figure 1). Furthermore, recent isolated and, consequently, have received widespread anthropogenic habitat changes and increasing human political and conservation attention (Oyler-McCance et presence (i.e., development and park visitation rates) al. 2005; Walker et al. 2007; Aldridge et al. 2008). In have occurred in areas immediately adjacent to Jackson, 2010, the United States Fish and Wildlife Service potentially increasing the distance to larger sage-grouse determined that sage-grouse deserved protection under populations to the south (i.e., Sublette County). This is the Endangered Species Act, yet protection was Figure 1. Approximate locations of sage-grouse populations precluded due to higher priority cases. It is currently a sampled throughout Wyoming with sample size in 2 Schulwitz et al.: Low Neutral Genetic Diversity in an Isolated Greater Sage Grouse 121 Jackson Hole (n = 57) and Gros Ventre (n=16; Teton County), from three locations near Pinedale (Sublette County) designated north (n = 24), south (n = 28), and west (n = 27) Pinedale, west of Casper (n = 25; Natrona County), and in Powder River Basin east of Buffalo (Johnson

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