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Morphometric measurements were used to classify 11 mustelid dentaries from Snake Creek Burial Cave (SCBC), a late Pleistocene to early Holocene—aged paleontological locality in eastern Nevada, that were undifferentiated between Mustela nigripes (black-footed ferret) and Neovison vison (American mink) due to their similar size and morphology. We, therefore, classified the SCBC fossils using 10 linear measurements of the dentary using extant M. nigripes and N. vison as proxy. Discriminant function and principal component analyses grouped the 11 unknown SCBC specimens within extant M. nigripes exclusively. Confirmation of M. nigripes at SCBC is significant because Cynomys spp. (their primary prey source today) have not been found at this site or other nearby Great Basin localities. Occurrence of this now-endangered taxon among the SCBC paleofauna and review of additional localities lacking Cynomys suggest that several geographically and temporally discrete prehistoric M. nigripes populations were sustained by other small mammal taxa. If this inference is true, facilitating dietary diversity in reintroduced M. nigripes populations could improve the species' resilience to future adversities, including anthropogenic climate change.
The Mohave ground squirrel (Xerospermophilus mohavensis) is endemic to the western Mojave Desert of California and is state-listed as Threatened. This species is of conservation concern because of the potential for large-scale renewable energy development within its range. Recent evidence suggests that this threatened species may at least occasionally hybridize with the closely related round-tailed ground squirrel (Xerospermophilus tereticaudus) where the species come into contact. As a result, there is great interest in the distribution of the Mohave ground squirrel, especially where it may come in contact with the round-tailed ground squirrel. One of the least understood portions of the Mohave ground squirrel distribution is around the Hinkley Valley, west of the city of Barstow, where its eastern range limits come into proximity with the round-tailed ground squirrel. To document what is known of the fine-scale distribution of these congeners in this region, we assemble and review all available trapping survey data from this area and combine the field survey data with genetic analyses of recently collected samples. Our evaluation of trapping records confirms that there are no reliable recent reports of Mohave ground squirrels in the Hinkley Valley itself, which has been developed for agriculture. The species appears to be largely restricted to the relatively undisturbed desert habitat west of Hinkley. In contrast, a number of round-tailed ground squirrel records exist for the Hinkley Valley, some dating back to 1977. Using 13 nuclear microsatellite loci from 55 ground squirrel samples collected across this region, we confirm the presence of genetically pure Mohave and round-tailed ground squirrels. However, 3 individuals collected in the Hinkley Valley that were identified as round-tailed ground squirrels on the basis of external characteristics show evidence of Mohave ground squirrel ancestry. In similar fashion, 3 animals from the desert region west of Hinkley were found to have some round-tailed ground squirrel genetic ancestry in spite of external features typical of Mohave ground squirrels. While round-tailed ground squirrels seem to be the dominant species in Hinkley Valley and Mohave ground squirrels seem dominant in the desert environment to the west, hybridization does appear to occur occasionally. Further, when these species hybridize, at least some hybrids are fertile, and backcrossing appears to occur in both parental directions. It is important to investigate this phenomenon more closely to evaluate possible threats to the genetic integrity of the Mohave ground squirrel.
In Dixie Valley, Nevada, an isolated population of toads has been the subject of proactive conservation measures by the Nevada Department of Wildlife and the U.S. Fish and Wildlife Service since 2008 due to concerns about potential habitat degradation resulting from exploitation of nearby geothermal energy resources. These toads appear to belong within the Anaxyrus boreas species group but are commonly referred to as Dixie Valley toads (DVTs). The DVT is currently confined to an extremely narrow habitat range (370 ha) that is geographically isolated from any other A. boreas population. In this study, genetic variations in mitochondrial genes and 11 microsatellite loci were used to assess the affinities of DVTs in relation to members of the A. boreas species group. We compared results from DVTs with previously published data spanning much of the range of A. boreas in the United States and new data from a nearby toad population within Dixie Valley. Data from both mitochondrial DNA and microsatellites placed DVTs inside the A. boreas species group. In particular, DVTs fell into a cluster of A. boreas from Washington and California, along with other species from the A. boreas species group, namely A. nelsoni, A. canorus, and A. exsul. Genetic differentiation of DVTs was lowest between A. boreas populations in Washington and California. However, allele frequencies were significantly different between DVTs and all other populations, including a nearby locality within Dixie Valley. This genetic differentiation, along with the DVT's geographical isolation and restricted habitat, warrants recognition of the DVT as a distinct management unit.
Seasonal wetlands are important habitats for biodiversity of both invertebrate and vertebrate fauna. Many aquatic species have life history traits adapted to colonizing and developing in temporary aquatic habitats, and these traits influence the annual succession of the macroinvertebrate community. The chronology of taxon appearance and the variation in relative abundances during the hydroperiod are important for understanding population dynamics, trophic interactions, and responses to drought. This study investigated the successional changes in macroinvertebrate abundances in a seasonal wetland in northern California. Water quality parameters were measured regularly, including dissolved oxygen, temperature, pH, surface area, and specific conductance during the wet season ( January–July) in 2007–2009. Macroinvertebrates were collected with net sweeps (mesh > 500 mm), and the presence of life stages of amphibians were visually observed from March to June each year. As the hydroperiod progressed, wetland surface area decreased, while water temperature and specific conductance increased. Macroinvertebrate abundance increased with the progression of the hydroperiod, and the richness of macroinvertebrate predator taxa tripled from 2 families in March to 6 families in June. The earliest part of the hydroperiod in the wetland was dominated by Cyzicus clam shrimp and Linderiella occidentalis fairy shrimp. Limnephilus caddisfly larvae were few in number but were found exclusively in the early season. Sequential changes of dominant invertebrate taxa and relative abundances of macroinvertebrates were evident, particularly among several macroinvertebrate predators. Among these predators, the early-season community was dominated by larval dytiscid beetles, while later-season communities demonstrated increased predator richness (e.g., Notonecta backswimmers) and were dominated by Lestes damselflies. Larvae of the vertebrate predator Taricha torosa, which may act as a top predator, were present during the later stages of the hydroperiod. The phenology of individual aquatic taxa and their specific life history strategies may impact the sensitivity of macroinvertebrate populations to increased annual variation in hydroperiod that may result from climate changes in this region.
Utah chub Gila atraria is native to the Upper Snake River system in Wyoming and Idaho and to the Lake Bonneville Basin in Utah and southeastern Idaho. However, the Utah chub has been introduced into many other waterbodies in the western United States, where it competes with ecologically and economically important species. The objectives of this study were to evaluate between-reader precision and reader confidence in age estimates obtained from pectoral fin rays, lapilli (otoliths), asterisci (otoliths), and scales for Utah chubs collected from Henrys Lake, Idaho. Lapilli have been previously shown to provide accurate age estimates for Utah chubs; therefore, we sought to compare age estimates from fin rays, asterisci, and scales to those from lapilli. The between-reader coefficient of variation (CV) in age estimates was lowest and the percent of exact reader agreement (PA-0) was highest for pectoral fin rays (CV = 4.7, PA-0 = 74%), followed by scales (CV = 10.3, PA-0 = 52.3%), lapilli (CV = 11.6, PA-0 = 48.2%), and asterisci (CV = 13.0, PA-0 = 41.7%). Consensus age estimates from pectoral fin rays showed high concordance with consensus age estimates from lapilli. Our results indicate that pectoral fin rays provide the most precise age estimates for Utah chub. Pectoral fin rays are easily collected and processed and also provide age estimates without requiring fish sacrifice.
Sampling the density and basal area of trees is fundamental to quantitatively characterizing forests and woodlands. Commonly used sampling methods are well-suited for trees with single trunks, but are these methods also suitable for sampling multi-trunked trees? This question is especially important where multi-trunked trees are common, as is the case for Utah juniper ( Juniperus osteosperma, JUOS), a codominant of large areas of pinyon-juniper vegetation in western North America. This study addresses the question of suitability by comparing 3 methods for sampling JUOS. The Dbase Method has been commonly used, and it focuses on the bases of trees for both identifying individuals and measuring tree diameters. The Dbh Method, which parallels the standard for sampling single-trunked tree species, also has been used for multi-trunked trees, and it focuses on breast height (i.e., 1.4 m above ground) for both identifying individuals and measuring diameters. The third method, the Base-Dbh Method, is proposed as a possible improvement. It focuses on the bases of trees for identifying individuals and on breast height for measuring diameters. Application of these 3 methods to the same JUOS trees produced statistically significant differences in values of density and basal area and thereby also produced differences in relative values (when JUOS was compared to the codominant two-needle pinyon, Pinus edulis). Comparison of the 3 methods determined that the proposed Base-Dbh Method is superior in terms of (1) biological validity, (2) comparability to data from single-trunked tree species, and (3) consistent application by field personnel.
We found 13 specimens (11 museum skins, 2 skeletons) of White-tailed Ptarmigan (Lagopus leucura) collected in Wyoming. All were collected in the 1911–1967 period: 12 from the Snowy Range (Albany County) and one from near Encampment (Carbon County). The last verifiable observations of White-tailed Ptarmigan in the Snowy Range were 2 separate reports in 1974, both of 4 individuals in the same location. A more recent report of 2 birds north of the Snowy Range on 15 October 2005 has also been verified. None of the verifiable observations or collection events was of more than 6 individuals. Most of the published observation records from areas other than in the Snowy Range were of single individuals and were likely Dusky Grouse (Dendragapus obscurus). Field investigations in the Beartooth Plateau, Bighorn Mountains, and Wind River Range outside of the Snowy Range revealed no ptarmigan or their sign. However, all unoccupied areas examined could potentially support White-tailed Ptarmigan populations, with the Wind River Range being most suitable, followed by the Bighorn Mountains and Beartooth Plateau. The lack of White-tailed Ptarmigan in alpine areas in Wyoming outside of the Snowy Range is most likely related to geologic events in the late Pleistocene period and not in the Holocene.
Western juniper woodlands have been the focus of extensive research and management due to range expansion and infilling that began over a century ago. Understanding juniper seed dispersal is vital to identifying processes behind this expansion. Dispersal of Juniperus seeds has generally been attributed to consumption of female juniper cones (“berries”) by frugivorous birds and mammals, which then defecate seeds after gut passage. However, recent studies have found that scatter-hoarding rodents harvest and cache juniper seeds. Rodents caching and failing to recover juniper seeds that have been removed from feces may constitute a secondary mode of dispersal that accounts for more seedling recruitment than primary dispersal by frugivores. We considered implications of juniper seed dispersal by frugivorous birds and subsequent removal of bird-passed seeds and secondary dispersal by scatter-hoarding rodents by examining the distribution of western juniper seeds after dispersal by birds along transects extending from a juniper woodland into a 30-year-old burn. In winter 2016, we surveyed 4 microsites (open, shrub canopy, juniper canopy, and rock) across the wooded and burned habitats for bird-dispersed seeds and repeated surveys 6 months later to determine the degree to which rodents had removed seeds. Western juniper seeds were more abundant in winter than in summer surveys, in the woodland than in the burned habitat, and under juniper canopies compared with the other microsites. There was a significant inverse relationship between the number of bird-dispersed seeds in each microsite and the distance of the microsite from the woodland. We suggest that scatter-hoarding rodents are important to the dispersal process, as they remove seeds from high-density microsites, such as tree canopies, and redistribute them. We consider the relevance of these findings to western juniper woodlands experiencing infilling and expansion, as well as to those impacted by climate-induced mortality.
The general lack of trees in the Great Plains has limited colonization by eastern woodland mammals in the past, but recent expansion of forests in corridors along prairie waterways and in towns has enabled an assortment of woodland species to expand distributional ranges westward. The evening bat (Nycticeius humeralis) historically occurred in woodlands throughout the eastern United States. Following our capture of the first evening bat in New Mexico, we updated the distributional range for this species by amassing recent records from published literature and museum voucher records west of its historic range published in 1981, the last time the species distribution was updated throughout its range. We document that evening bats, including some reproductively active populations, now occur across much of the central and southern Great Plains, including southwestern Nebraska, western Kansas, and western Texas. Such records should encourage researchers to factor in the possible occurrence of this species beyond published historic western limits for mist-netting and acoustic surveys. While it remains unclear if the single capture in southwestern New Mexico represented a wandering individual, these compiled records suggest that established populations might occur west of our updated distribution for the species.
Burrow-nesting birds are limited by access to nest sites, particularly in years of very high humidity levels, such those seen with El Niño, or in forests that are fragmented due to the effects of human activity. We assessed the breeding success of Momotus mexicanus nesting along the earth bank of a secondary road corridor in a seasonally dry tropical forest in Central Mexico. We monitored 28 nests during the reproductive period and characterized the composition of the soil where they were constructed, as well as other physical variables. One nest produced 2 fledglings, and the other 27 failed to produce any: 46% of the nests experienced flooding or wall collapses, while the nests built on sandy loam soil remained intact. We also report other basic natural history variables for these neotropical burrow-nesting birds.
Estimation of connectivity for multiple species could increase the efficiency of resource management and elucidate trade-offs among maintenance of connectivity for different taxa. We identified potential areas of high connectivity for 5 species of mammals on the Navajo Nation and adjacent lands in Utah, Arizona, and New Mexico, USA: mountain lion (Puma concolor), mule deer (Odocoileus hemionus), desert bighorn sheep (Ovis canadensis nelsoni), American black bear (Ursus americanus), and pronghorn (Antilocapra americana). These species were identified by the Navajo Nation as relevant to the benefit of their present and future generations. We used telemetry data to calculate utilization distributions, derive model permeability (the probability that a given location facilitates animal movement), and assess connectivity (the realization of permeability across a landscape) for desert bighorn sheep, black bear, and pronghorn. We based models of connectivity for mountain lion and mule deer on expert-identified environmental variables and corresponding permeability values. We used Circuitscape software to model omnidirectional connectivity for each species, and then used maps of connectivity to identify potential dispersal areas. Different environmental features were associated with connectivity for each species. The rank correlation between the geographic distribution of connectivity for pairs of species ranged from −0.45 to 0.95. All but one of the estimated pairwise overlaps in potential dispersal areas were greater than would be expected if dispersal areas for each species were independent. The percentage of overlap generally decreased as a greater number of species was considered, but was greater than expected in 6 of 10 cases for 3 species and all cases for 4 or 5 species. Potential dispersal areas for all 5 species occurred within 83 km2 of the approximately 72,000-km2 analysis area. Our work illustrates use of a flexible method for estimating connectivity and potential dispersal areas, particularly where data on the distribution and movements of populations are limited.
Although the American pika (Ochotona princeps) continues to receive attention due to documented declines and range retractions, particularly in the Great Basin, thorough range inventories have yet to be completed in many parts of the region. Here we report on recently discovered populations in northwestern Nevada in areas not suspected to support pika activity under current climate regimes. We describe 238 new locations (“sites”) with evidence of past or current occupancy by pikas which cluster into 31 locales, which we interpret as metapopulations or “demes,” in 15 distinct mountain ranges or geographic areas. We documented twice as many relict sites (sites with evidence of former pika occupancy) as currently occupied sites, a result that supports previous observations of local range retraction and site losses within the pika's range. In the overall site data, median elevation and water year precipitation were higher and minimum and maximum July temperatures were lower for occupied sites than for relict sites. This pattern was repeated in most, but not all, of the 7 mountain ranges where both occupied and relict sites were found. Occupied sites were more likely to be found in areas with a narrow range of water year precipitation, in cooler climates, and on more mesic-facing aspects, but many of these environmental descriptors also describe relict sites. The apparent extirpation of pikas from the range with the highest elevation and lowest temperatures (Black Rock Range) and the continued persistence in some of the lowest and hottest areas of our survey (Home Camp Range) are particularly noteworthy. Since pikas were known from only a handful of early 20th century records in the area, these surveys greatly expand our understanding of both current and historic pika distributions in the northwestern Great Basin and shed light on patterns of pika persistence and extirpation in a region typified by harsher climates respective to other areas with extant pika populations. Furthermore, our results emphasize the importance of conducting spatially extensive fieldwork to better understand site extirpations and species range retractions.
We collected a single specimen of the giant water bug Belostoma flumineum Say 1832 (Hemiptera: Belostomatidae) during routine macroinvertebrate biomonitoring in the Souris River, Saskatchewan. This is the first record of B. flumineum in the province of Saskatchewan and represents a more northern record than the previously documented locations in Montana, North Dakota, and southeastern Manitoba.
Because limited numbers of netleaf hackberry (Celtis reticulata) seedlings are observed in nature, we evaluated patterns of germination of hackberry seeds (n = 2545) that we planted near boulders in the Wasatch Mountain foothills. Seeds were followed over 2 growing seasons. Germination rates were very low overall, but significantly more seeds germinated on the north sides of boulders compared to other boulder aspects. That we found higher rates of germination on the north sides of boulders, instead of on the south sides of boulders where mature hackberry shrubs tend to grow, could reflect year-to-year variation in seed germination and seedling survival but is also consistent with a shift away from warmer and drier sites by hackberry in response to climate change.