Effects of ungulates and prairie dogs on seed banks and vegetation in a North American mixed-grass prairie

The relationship between vegetation cover and soil seed banks was studied in five different ungulate herbivore-prairie dog treatment combinations at three northern mixed-grass prairie sites in Badlands National Park, South Dakota. There were distinct differences in both the seed bank composition and the aboveground vegetation between the off-prairie dog colony treatments and the on-colony treatments. The three on-colony treatments were similar to each other at all three sites with vegetation dominated by the forbs Dyssodia papposa, Hedeoma spp., Sphaeralcea coccinea, Conyza canadensis, and Plantago patagonica and seed banks dominated by the forbs Verbena bracteata and Dyssodia papposa. The two off-colony treatments were also similar to each other at all three sites. Vegetation at these sites was dominated by the grasses Pascopyrum smithii, Bromus tectorum and Bouteloua gracilis and the seed banks were dominated by several grasses including Bromus tectorum, Monroa squarrosa, Panicum capillare, Sporobolus cryptandra and Stipa viridula. A total of 146 seedlings representing 21 species germinated and emerged from off-colony treatments while 3069 seedlings comprising 33 species germinated from on-colony treatments. Fifteen of the forty species found in soil seed banks were not present in the vegetation, and 57 of the 82 species represented in the vegetation were not found in the seed banks. Few dominant species typical of mixed-grass prairie vegetation germinated and emerged from seed banks collected from prairie dog colony treatments suggesting that removal of prairie dogs will not result in the rapid reestablishment of representative mixed-grass prairie unless steps are taken to restore the soil seed bank.     

Interactive disturbance effects of two disparate ecosystem engineers in North American shortgrass steppe

Disturbances such as fire, grazing, and soil mixing by animals interact to shape vegetation in grassland ecosystems. Animal-generated disturbances are unique in that they arise from a suite of behaviors that are themselves subject to modification by external factors. The manner in which co-occurring animal taxa interact to alter vegetation is a function of their respective behaviors, which shape the characteristics (e.g., the magnitude or extent) of their disturbances. To determine whether prairie dogs (Cynomys ludovicianus) and harvester ants (Pogonomyrmex occidentalis) interactively alter vegetation structure and heterogeneity on the Colorado shortgrass steppe, we characterized the size, dispersion, and vegetation of prairie dog burrow mounds and ant nests (located on and off prairie dog colonies) and vegetation growing beyond mound and nest perimeters. Ants located on prairie dog colonies engineered significantly larger nests and disturbed nearly twice as much total soil area as their off-colony counterparts. Ant nests were overdispersed both on and off prairie dog colonies, while prairie dog mounds were randomly dispersed. Where harvester ants and prairie dogs co-occur, the overdispersed pattern of on-colony ant nests is in effect "overlaid" onto the random pattern of prairie dog mounds, resulting in a unique, aggregated pattern of soil disturbance. Ant nests on prairie dog colonies had significantly less vegetation and lower plant species diversity than did prairie dog mounds, while off-colony nests were similar to mounds. These results suggest that ant nests are more highly disturbed when located on prairie dog colonies. Beyond nests proper, ants did not appear to alter vegetation in a manner distinct from prairie dogs. As such, the interactive effects of prairie dogs and ants on vegetation arise mainly from the disturbance characteristics of mounds and nests proper.     

Black-Tailed Prairie Dogs,Cattle, and the Conservation of North America’s Arid Grasslands

Prairie dogs (Cynomys spp.) have been eliminated from over 95% of their historic range in large part from direct eradication campaigns to reduce their purported competition with cattle for forage. Despite the longstanding importance of this issue to grassland management and conservation, the ecological interactions between cattle and prairie dogs have not been well examined. We address this issue through two complementary experiments to determine if cattle and prairie dogs form a mutualistic grazing association similar to that between prairie dogs and American bison. Our experimental results show that cattle preferentially graze along prairie dog colony edges and use their colony centers for resting, resembling the mutualistic relationship prairie dogs have with American bison. Our results also show that prairie dog colonies are not only an important component of the grassland mosaic for maintaining biodiversity, but also provide benefits to cattle, thereby challenging the long-standing view of prairie dogs as an undesirable pest species in grasslands.     

Ecosystem engineering varies spatially: a test of the vegetation modification paradigm for prairie dogs

Colonial, burrowing herbivores can be engineers of grassland and shrubland ecosystems worldwide. Spatial variation in landscapes suggests caution when extrapolating single‐place studies of single species, but lack of data and the need to generalize often leads to ‘model system’ thinking and application of results beyond appropriate statistical inference. Generalizations about the engineering effects of prairie dogs (Cynomys sp.) developed largely from intensive study at a single complex of black‐tailed prairie dogs C. ludovicianus in northern mixed prairie, but have been extrapolated to other ecoregions and prairie dog species in North America, and other colonial, burrowing herbivores. We tested the paradigm that prairie dogs decrease vegetation volume and the cover of grasses and tall shrubs, and increase bare ground and forb cover. We sampled vegetation on and off 279 colonies at 13 complexes of 3 prairie dog species widely distributed across 5 ecoregions in North America. The paradigm was generally supported at 7 black‐tailed prairie dog complexes in northern mixed prairie, where vegetation volume, grass cover, and tall shrub cover were lower, and bare ground and forb cover were higher, on colonies than at paired off‐colony sites. Outside the northern mixed prairie, all 3 prairie dog species consistently reduced vegetation volume, but their effects on cover of plant functional groups varied with prairie dog species and the grazing tolerance of dominant perennial grasses. White‐tailed prairie dogs C. leucurus in sagebrush steppe did not reduce shrub cover, whereas black‐tailed prairie dogs suppressed shrub cover at all complexes with tall shrubs in the surrounding habitat matrix. Black‐tailed prairie dogs in shortgrass steppe and Gunnison's prairie dogs C. gunnisoni in Colorado Plateau grassland both had relatively minor effects on grass cover, which may reflect the dominance of grazing‐tolerant shortgrasses at both complexes. Variation in modification of vegetation structure may be understood in terms of the responses of different dominant perennial grasses to intense defoliation and differences in foraging behavior among prairie dog species. Spatial variation in the engineering role of prairie dogs suggests spatial variation in their keystone role, and spatial variation in the roles of other ecosystem engineers. Thus, ecosystem engineering can have a spatial component not evident from single‐place studies.     

Plant-herbivore interactions in a North American mixed-grass prairie

Summary Studies were conducted during the 1979 growing season to examine how North American bison (Bison bison) use prairie dog (Cynomys ludovicianus) colonies in Wind Cave National Park, South Dakota. Objectives included (1) determining whether bison selected for prairie dog towns parkwide; (2) characterizing in greater detail bison use patterns of a 36-ha colony in Pringle Valley as a function of time since prairie dog colonization; and (3) relating these bison use patterns to measured changes in structure and nutritional value of vegetation on and off the dog town.During midsummer, prairie dog towns were one of the most frequently used habitats by bison parkwide. Day-long observations at Pringle Valley revealed that bison exerted strong selection (nearly 90% of all habitat use and feeding time) for the dog town, which occupied only 39% of the valley. While there, they partitioned their use of the colony by grazing in moderately affected areas (occupied <8 years by prairie dogs) and by resting in the oldest area (>26 years occupation).Prairie dogs facilitate bison habitat selection for a shortgrass successional stage in this mixed-grass community by causing a broad array of compositional, structural, and nutritional changes in the vegetation.     

Geographic variation in rodent-flea relationships in the presence of black-tailed prairie dog colonies

We characterized the relationship between fleas and their rodent hosts in the presence of prairie dog colonies and compared them to adjacent assemblages away from colonies. We evaluated the rodent-flea relationship by quantifying prevalence, probability of infestation, flea load, and intensity of fleas on rodents. As prairie dog burrows provide refugia for fleas, we hypothesized that prevalence, flea load, and intensity would be higher for rodents that are associated with black-tailed prairie dog colonies. Rodents were trapped at off- and on-colony grids, resulting in the collection of 4,509 fleas from 1,430 rodents in six study areas. The rodent community composition varied between these study areas. Flea species richness was not different between prairie dog colonies and the surrounding grasslands (p = 0.883) but was positively correlated with rodent species richness (p = 0.055). Prairie dog colonies did not increase the prevalence of fleas (p > 0.10). Flea loads on rodents did not vary between off- and on-colony grids at three of the study areas (p > 0.10). Based on the prevalence, infestation rates, and flea loads, we identified Peromyscus maniculatus, Onychomys leucogaster, and two Neotoma species as important rodent hosts for fleas and Aetheca wagneri, Orchopeus leucopus, Peromyscopsylla hesperomys, Pleochaetis exilis, and Thrassisfotus as the most important fleas associated with these rodents. Prairie dog colonies did not seem to facilitate transmission of fleas between rodent hosts, and the few rodent-flea associations exhibited significant differences between off- and on-colony grids.     

Spatial Analysis of Effects of Mowing and Burning on Colony Expansion in Reintroduced Black‐Tailed Prairie Dog (Cynomys ludovicianus)

Factors governing the rate and direction of prairie dog (Cynomys spp.) colony expansion remain poorly understood. However, increased knowledge and ability to control these factors may lead to more effective reintroductions of prairie dogs and restoration of grassland habitats. We present density and directional analyses of the establishment of new burrows on three reintroduced colonies of Black‐tailed prairie dog (Cynomys ludovicianus) in southern New Mexico; the study colonies had been subjected to mow and burn treatments in the second year of the study. Our hypotheses were that prairie dogs will preferentially dig new burrows in the treatment plots versus control plots and that the colonies will expand in the direction of the treatment plots. The results support these hypotheses; analysis of burrow counts by site and treatment shows that prairie dogs preferentially colonized both mow and burn treatments compared to untreated areas at the periphery of the colonies. Directional analysis showed a significant posttreatment orientation of new burrows toward the treatment plots for all colonies. Our results show that the direction of expansion of prairie dog colonies can be manipulated. Effective control of the expansion of prairie dog colonies may lead to more successful reintroductions.     

Reintroducing a keystone burrowing rodent to restore an arid North American grassland: challenges and successes

Prairie dogs (Cynomys spp.) are important ecosystem engineers in North America's central grasslands, and are a key prey base for numerous predators. Prairie dogs have declined dramatically across their former range, prompting reintroduction efforts to restore their populations and ecosystem functions, but the success of these reintroductions is rarely monitored rigorously. Here, we reintroduced 2,400 Gunnison's prairie dogs (C. gunnisoni) over a period of 6 years to the Sevilleta National Wildlife Refuge, in central New Mexico, U.S.A., a semi‐arid grassland ecosystem at the southern edge of their range. We evaluated the population dynamics of prairie dogs following their reintroduction, and their consequent effects on grassland vertebrates. We found postrelease survival of prairie dogs stabilized at levels typical for the species (ca. 50%) after approximately 1 month, while average annual recruitment was ca. 0.35 juveniles per female, well below what was required for a self‐sustaining, stable population. Extreme drought conditions during much of the study period may have contributed to low recruitment. However, recruitment increased steadily over time, indicating that the reintroduced colony may simply need more time to establish in this arid system. We also found well‐known associates of prairie dog colonies, such as American badgers (Taxidea taxus) and burrowing owls (Athene cunicularia), were significantly more common on the colonies than off. After 7 years, we have yet to meet our goal of establishing a self‐sustaining population of Gunnison's prairie dogs in this semi‐arid grassland. But despite the uncertainty and challenges, our work shows that reestablishing keystone species can promote ecosystem restoration.     

Rapid Decline of a Grassland System and Its Ecological and Conservation Implications

One of the most important conservation issues in ecology is the imperiled state of grassland ecosystems worldwide due to land conversion, desertification, and the loss of native populations and species. The Janos region of northwestern Mexico maintains one of the largest remaining black-tailed prairie dog (Cynomys ludovicianus) colony complexes in North America and supports a high diversity of threatened and endangered species. Yet, cattle grazing, agriculture, and drought have greatly impacted the region. We evaluated the impact of human activities on the Janos grasslands, comparing changes in the vertebrate community over the last two decades. Our results reveal profound, rapid changes in the Janos grassland community, demonstrating large declines in vertebrate abundance across all taxonomic groups. We also found that the 55,000 ha prairie dog colony complex has declined by 73% since 1988. The prairie dog complex has become increasingly fragmented, and their densities have shown a precipitous decline over the years, from an average density of 25 per ha in 1988 to 2 per ha in 2004. We demonstrated that prairie dogs strongly suppressed woody plant encroachment as well as created open grassland habitat by clearing woody vegetation, and found rapid invasion of shrubland once the prairie dogs disappeared from the grasslands. Comparison of grasslands and shrublands showed markedly different species compositions, with species richness being greatest when both habitats were considered together. Our data demonstrate the rapid decline of a grassland ecosystem, and documents the dramatic loss in biodiversity over a very short time period concomitant with anthropogenic grassland degradation and the decline of a keystone species.     

Occupancy of Mountain Plover and Burrowing Owl in Colorado

Abstract: Concern over the decline of grassland birds has spurred efforts to increase understanding of grassland bird-habitat relationships. Previous studies have suggested that black-tailed prairie dogs (Cynomys ludovicianus) provide important habitat for shortgrass prairie avifauna, such as mountain plover (Charadrius montanus) and western burrowing owl (Athene cunicularia hypugaea), although such studies are lacking in Colorado (USA). We used methods to estimate occupancy (ψ) of mountain plover and burrowing owl on prairie dog colonies and other shortgrass prairie habitats in eastern Colorado. Mountain plover occupancy was higher on prairie dog colonies (ψ = 0.50, 95% CI = 0.36–0.64) than on grassland (ψ = 0.07, 95% CI = 0.03–0.15) and dryland agriculture (ψ = 0.13, 95% CI = 0.07–0.23). Burrowing owl occupancy was higher on active prairie dog colonies (ψ = 0.80, 95% CI = 0.66–0.89) compared with inactive colonies (ψ = 0.23, 95% CI = 0.07–0.53), which in turn was much higher than on grassland (ψ = 0.01, 95% CI = 0.00–0.07) and dryland agriculture (ψ = 0.00, 95% CI ψ 0.00–0.00). Mountain plover occupancy also was positively correlated with increasing amounts of prairie dog colony in the landscape. Burrowing owl occupancy was negatively correlated with increasing amounts of prairie dog colony in the surrounding landscape. Our results suggest that actions to conserve mountain plovers and burrowing owls should incorporate land management to benefit prairie dogs. Because managing for specific colony attributes is difficult, alternative management that promotes heterogeneity may ensure that suitable habitat is available for the guild of grassland inhabitants.     

Prairie dog presence affects occurrence patterns of disease vectors on small mammals

Wildlife disease is recognized as a burgeoning threat to imperiled species and aspects of host and vector community ecology have been shown to have significant effects on disease dynamics. The black‐tailed prairie dog is a species of conservation concern that is highly susceptible to plague, a flea‐transmitted disease. Prairie dogs (Cynomys) alter the grassland communities in which they exist and have been shown to affect populations of small rodents, which are purported disease reservoirs. To explore potential ecological effects of black‐tailed prairie dogs on plague dynamics, we quantified flea occurrence patterns on small mammals in the presence and absence of prairie dogs at 8 study areas across their geographic range. Small mammals sampled from prairie dog colonies showed significantly higher flea prevalence, flea abundance, and relative flea species richness than those sampled from off‐colony sites. Successful plague transmission likely is dependent on high prevalence and abundance of fleas that can serve as competent vectors. Prairie dogs may therefore facilitate the maintenance of plague by increasing flea occurrence on potential plague reservoir species. Our data demonstrate the previously unreported ecological influence of prairie dogs on vector species assemblages, which could influence disease dynamics.     

Disturbance regimes and mountain plover habitat in shortgrass steppe: Large herbivore grazing does not substitute for prairie dog grazing or fire

Restoring historical disturbance regimes to enhance habitat for grassland birds can conflict with livestock production goals and has been controversial because of uncertainty in the frequency and pattern of different disturbances prior to European settlement. We studied nesting habitat for the mountain plover (Charadrius montanus) in relation to prescribed fire, grazing by large herbivores (cattle), and grazing by black-tailed prairie dogs (Cynomys ludovicianus) in the shortgrass steppe of northeastern Colorado. Breeding mountain plovers primarily occurred on black-tailed prairie dog colonies or areas burned during the previous dormant season. Vegetation surrounding mountain plover nests and foraging locations was characterized by a fine-scale mosaic of prostrate (<4 cm tall) vegetated patches interspersed with >35% bare soil in a given square meter, with this fine-scale pattern distributed over a broad (>100-m radius) area. Mountain plovers rarely occupied grassland lacking prairie dogs or recent fire, but those that did selected sites with similar vegetation height and bare soil exposure as sites on burns and prairie dog colonies. Vegetation structure at mountain plover-occupied sites was also similar to random sites on burns and prairie dog colonies, but differed substantially from sites managed only with cattle. Intensive cattle grazing at twice the recommended stocking rate during spring (Mar–May) or summer (May–Oct) for 6 years produced significantly less bare soil than burns and prairie dog colonies, particularly following years with average or above-average precipitation. Thus, intensive cattle grazing did not substitute for prairie dog grazing or fire in terms of effects on vegetation structure and mountain plover habitat. Both prescribed burning and increased size and distribution of black-tailed prairie dog colonies appear to be effective and complementary means to manage for mountain plover breeding habitat in shortgrass steppe. Provision of mountain plover habitat has tradeoffs with traditional management for livestock production. Thus, managers need to clearly define desired outcomes for management to provide multiple ecosystem goods and services. © 2012 The Wildlife Society.     

Plant community responses to bison reintroduction on the Northern Great Plains,United States: a test of the keystone species concept

Keystone species restoration, or the restoration of species whose effect on an ecosystem is much greater than their abundance would suggest, is a central justification for many wildlife reintroduction projects globally. Following restoration, plains bison (Bison bison L.) have been identified as a keystone species in the tallgrass prairie ecoregion, but we know of no research to document similar effects in the mixed‐grass prairie where restoration efforts are ongoing. This study addresses whether Northern Great Plains (NGP) mixed‐grass prairie plant communities exhibit traits consistent with four central keystone effects documented for bison in the tallgrass prairie. We collected species composition, diversity, abundance, bare ground cover, and plant height data in three treatments: where livestock (Bos taurus L.) continuously grazed, livestock were removed for 10 years, and bison have been introduced and resident for 10 years. We observed mixed support for bison acting as keystone species in this system. Supporting the keystone role of bison, we observed higher species richness and compositional heterogeneity (β‐diversity) in the bison treatment than either the livestock retention or livestock removal treatments. However, we observed comparable forb, bare ground, and plant height heterogeneity between bison‐restored sites and sites where livestock were retained, contradicting reported keystone effects in other systems. Our results suggest that after 10 years of being restored, bison partially fulfill their role as a keystone species in the mixed‐grass prairie, and we encourage continued long‐term data collection to evaluate their influence in the NGP.     

Rates of vegetation change associated with prairie dog (Cynomys ludovicianus) grazing in North American mixed-grass prairie

A prairie dog (Cynomys ludovicianus) colony with a known history of habitation was studied to quantify the effects of herbivory on plant species composition, dominance, stature and diversity in a North American mixedgrass prairie. Gradient analysis was used to quantify the relationship between plant community structure, prairie dog density, burrow density and habitation history and to document community-level responses of plants subjected to heavy grazing pressure. The results quantify the type, rate and extent of change which plant populations and communities may undergo in response to the differential grazing of plants variously tolerant of defoliation.Detrended correspondence analysis indicated that 69% of the between-sample floristic variance on the site was attributable to prairie dog habitation. Perennial grasses were rapidly displaced from the site within 3 yr of colonization and were replaced by annual forbs. The net result was an increase in species richness and diversity on the prairie dog colony. Within the colony, however, the number of species was more a function of stand size than colonization history.Significant decreases in canopy stature after 2 yr of habitation resulted from replacement of mid-height grass species by shortgrass species and forbs. In addition, there was a shift from tall growth forms of off-colony species to dwarf growth forms of the same species on the colony. Decreases in litter and increases in bare soil cover were substantial during the first 2 yr of habitation but changed little thereafter.Abbreviations WCC Wind Cave Canyon - DCA Detrended Correspondence Analysis     

Habitat use by Mountain Plovers in prairie dog colonies in northeastern New Mexico

ABSTRACT Mountain Plovers (Charadrius montanus) are grassland birds that often breed in close association with colonies of black‐tailed prairie dogs (Cynomys ludovicianus). However, not all colonies provide plover nesting habitat or habitat of equal quality, and the characteristics of colonies important for plovers remain poorly understood. Over two years, I used plover distribution surveys, territory mapping, and habitat sampling to study habitat use by plovers in prairie dog colonies in shortgrass prairie in northeastern New Mexico. My objective was to document important components of plover breeding habitat in colonies by comparing characteristics of used and unused habitats at three spatial scales: colony, territory, and nest‐site. I found evidence of plover breeding in 14 of 44 colonies in 2009 and 13 of 43 colonies in 2010. Based on logistic regression, the probability of a colony being occupied by plovers was positively associated with colony size, but negatively associated with mean vegetation height. Preference for larger colonies could relate to minimum habitat requirements, or a potential tendency of this species to nest in social clusters. Shorter vegetation height was strongly correlated with greater bare ground and lower forb/subshrub cover, all characteristics that may be related to plover predator avoidance and foraging microhabitat. At both the territory and nest‐site scale, areas used by plovers had shorter vegetation, more bare ground, and less forb/subshrub cover than unused areas. Nest sites were also more sloped, perhaps to reduce risk of flooding, and located further away from the nearest prairie dog burrow, perhaps to reduce risk of disturbance. Overall, my results show that plover use of prairie dog colonies was influenced by landscape and habitat features of colonies, and suggest that large colonies are particularly valuable because they are most likely to contain adequate areas with preferred habitat characteristics.     

The absence of concordant population genetic structure in the black‐tailed prairie dog and the flea,Oropsylla hirsuta,with implications for the spread of Yersinia pestis

The black‐tailed prairie dog (Cynomys ludovicianus) is a keystone species on the mid‐ and short‐grass prairies of North America. The species has suffered extensive colony extirpations and isolation as a result of human activity including the introduction of an exotic pathogen, Yersinia pestis, the causative agent of sylvatic plague. The prairie dog flea, Oropsylla hirsuta, is the most common flea on our study colonies in north‐central Montana and it has been shown to carry Y. pestis. We used microsatellite markers to estimate the level of population genetic concordance between black‐tailed prairie dogs and O. hirsuta in order to determine the extent to which prairie dogs are responsible for dispersing this potential plague vector among prairie dog colonies. We sampled fleas and prairie dogs from six prairie dog colonies in two regions separated by about 46 km. These colonies were extirpated by a plague epizootic that began months after our sampling was completed in 2005. Prairie dogs showed significant isolation‐by‐distance and a tendency toward genetic structure on the regional scale that the fleas did not. Fleas exhibited higher estimated rates of gene flow among prairie dog colonies than the prairie dogs sampled from the same colonies. While the findings suggested black‐tailed prairie dogs may have contributed to flea dispersal, we attributed the lack of concordance between the population genetic structures of host and ectoparasite to additional flea dispersal that was mediated by mammals other than prairie dogs that were present in the prairie system.     

Prevalence of Yersinia pestis in rodents and fleas associated with black-tailed prairie dogs (Cynomys ludovicianus) at Thunder Basin National Grassland, Wyoming

Rodents (and their fleas) that are associated with prairie dogs are considered important for the maintenance and transmission of the bacterium (Yersinia pestis) that causes plague. Our goal was to identify rodent and flea species that were potentially involved in a plague epizootic in black-tailed prairie dogs at Thunder Basin National Grassland. We collected blood samples and ectoparasites from rodents trapped at off- and on-colony grids at Thunder Basin National Grassland between 2002 and 2004. Blood samples were tested for antibodies to Y. pestis F-1 antigen by a passive hemagglutination assay, and fleas were tested by a multiplex polymerase chain reaction, for the presence of the plague bacterium. Only one of 1,421 fleas, an Oropsylla hirsuta collected in 2002 from a deer mouse, Peromyscus maniculatus, tested positive for Y. pestis. Blood samples collected in summer 2004 from two northern grasshopper mice, Onychomys leucogaster, tested positive for Y. pestis antibodies. All three positive samples were collected from on-colony grids shortly after a plague epizootic occurred. This study confirms that plague is difficult to detect in rodents and fleas associated with prairie dog colonies, unless samples are collected immediately after a prairie dog die-off.     

Connectivity of prairie dog colonies in an altered landscape: inferences from analysis of microsatellite DNA variation

Connectivity of populations influences the degree to which species maintain genetic diversity and persist despite local extinctions. Natural landscape features are known to influence connectivity, but global anthropogenic landscape change underscores the importance of quantifying how human-modified landscapes disrupt connectivity of natural populations. Grasslands of western North America have experienced extensive habitat alteration, fragmenting populations of species such as black-tailed prairie dogs (Cynomys ludovicianus). Population sizes and the geographic range of prairie dogs have been declining for over a century due to habitat loss, disease, and eradication efforts. In many places, prairie dogs have persisted in the face of emerging urban landscapes that carve habitat into smaller and smaller fragments separated by uninhabitable areas. In extreme cases, prairie dog colonies are completely bounded by urbanization. Connectivity is particularly important for prairie dogs because colonies suffer high probabilities of extirpation by plague, and dispersal permits recolonization. Here we explore connectivity of prairie dog populations using analyses of 11 microsatellite loci for 9 prairie dog colonies spanning the fragmented landscape of Boulder County, Colorado. Isolation-by-resistance modeling suggests that wetlands and high intensity urbanization limit movement of prairie dogs. However, prairie dogs appear to move moderately well through low intensity development (including roads) and freely through cropland and grassland. Additionally, there is a marked decline in gene flow between colonies with increasing geographic distance, indicating isolation by distance even in an altered landscape. Our results suggest that prairie dog colonies retain some connectivity despite fragmentation by urbanization and agricultural development.     

Investigating the distribution of prairie dogs in an urban landscape

Habitat fragmentation is a prevalent threat to biological diversity, and urbanization is a primary agent of fragmentation and a leading cause of species endangerment. Landscape biogeographic and local habitat characteristics can be important determinants of the distribution of species in habitat patches in urban landscapes. However, the specifics of which characteristics are most critical to maintaining biological diversity are not fully known for prairie ecosystems, especially in fragmented urban habitat. This study focuses on black-tailed prairie dogs along an urban gradient in Denver, CO. Prairie dogs have declined precipitously throughout the region and are an essential part of the prairie ecosystem, making them excellent study subjects. We identified a series of habitat fragments along a gradient of urbanization in the fully urbanized areas and south suburbs of Denver, CO, both containing and not containing prairie dogs. Local characteristics, including fragment slope and vegetative cover, and landscape characteristics, including fragment size, age and connectivity, were measured on each fragment. We used likelihood-based methods to explore which variables most accurately predicted prairie dog occurrence within our study area. Multiple factors influenced the distribution of prairie dogs in urban settings, with colony connectivity the strongest predictor of occupancy. Large and recently isolated fragments near other prairie dog colonies, flat areas and those with high graminoid cover were most likely to support prairie dog populations. Our study provides the first attempt to model prairie dog occurrence in highly fragmented urban habitat and has important implications for the management and conservation of prairie dogs.