Southwestern Wyoming Research Articles

An early Eocene fish fauna from the Bitter Creek area of the Wasatch Formation of southwestern Wyoming, U.S.A.

ABSTRACTEarly Eocene fluvial ichthyofaunas of Wyoming are relatively poorly known compared with the better-preserved lake deposits of the Green River Formation. We describe the teleost fishes from a single floodplain locality in the main body of the Wasatch Formation that immediately predates the formation of Lake Gosiute, in the Washakie Basin of Wyoming. This assemblage was deposited during the Graybullian substage of the Wasatchian Stage, corresponding to the onset of the rapid climatic warming leading to the Early Eocene Climatic Optimum. In addition to a lepisosteiform and an amiid, the locality has a teleost ichthyofauna comprising Diplomystus (Ellimmichthyiformes), a gonorynchiform probably representing Notogoneus, amblyopsid-like percopsiforms that may represent up to three taxa, and perciforms among which are probably an indeterminate centrarchid and ‘Priscacara.’ The fauna demonstrates that many of the Green River Formation fish taxa were already present in fluvial environments prior to the formation of the Green River lakes, indicating that the subsequent climate warming had little effect on these fishes. Some of the elements recognized here as probably representing Notogoneus were previously recovered from Late Cretaceous deposits from Utah to Alberta, suggesting that this gonorynchid was wide-ranging in North American fluvial environments since Mesozoic times, as were several other taxa identified here. Furthermore, the ichthyofauna indicates that the depositional environment was well vegetated and well oxygenated. These waters were shallow, with gentle flow strengths, which, together with the high oxygen content, suggests that the sediments of the locality were deposited in small ponds connected to an active river system.Citation for this article: Divay, J. D., and A. M. Murray. 2016. An early Eocene fish fauna from the Bitter Creek area of the Wasatch Formation of southwestern Wyoming, U.S.A. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2016.1196211.

Effectiveness of the toxicant DRC-1339 in reducing populations of common ravens in Wyoming

Common raven (Corvus corax) populations have increased several-fold in the western United States during the past century; these birds cause problems when they kill new-borne lambs and calves and depredate nests of greater sage-grouse (Centrocercus urophasianus). The toxicant DRC-1339 is used by U.S. Department of Agriculture/Animal and Plant Health Inspection Service Wildlife Services to manage common raven populations and reduce the severity of these problems, but it is difficult to determine how many ravens are killed by an application because carcasses are rarely found. We examined the effectiveness of DRC-1339 applications for preventative control of ravens at 3 landfills and 5 nearby roosts in Wyoming, USA, from 2013 through 2015. Wildlife Services removed 23%, 34%, and 7% of the radiomarked sample of ravens in southwestern Wyoming during 2013, 2014, and 2015, respectively, according to Kaplan–Meier survival estimates. During the 3 winters, 235 of 240 raven carcasses that we collected died from DRC-1339 poisoning. The following year, raven fecundity and immigration had offset most, but not all, of the mortality produced by the DRC-1339 program. Raven population estimates declined 9% from the 2013 winter to the 2014 winter and 12% from the 2014 winter to the 2015 winter, based on telemetry data and roost counts. Ravens did not avoid landfills after they were treated with DRC-1339 probably because few ravens died there. Estimated mortality rates from DRC-1339 applications based on carcass counts underestimated the actual rates by 79% and landfill counts of ravens underestimated it by 49%. Roost count estimates of mortality were within 15% of the actual mortality rate. © 2016 The Wildlife Society.

Sedimentary record of seismic events in the Eocene Green River Formation and its implications for regional tectonics on lake evolution (Bridger Basin, Wyoming)

Outcrops and cores from the top of the lacustrine Tipton Member and the base of the Wilkins Peak Member (~51.5Ma) of the Eocene Green River Formation, Bridger Basin in southwestern Wyoming yield a wide variety of sedimentary deformation features many of which are laterally extensive for more than 50km. They include various types of folds, load structures, pinch-and-swell structures, microfaults, breccias and sedimentary dikes. In most cases deformation is represented by hybrid brittle–ductile structures exhibiting lateral variation in deformation style. These occur in low-energy, profundal organic-rich carbonate mudstones (oil shales), trona beds, tuffs, and profundal to sublittoral silty carbonate deposited in paleolake Gosiute. The deformation is not specific to the depositional environment because sedimentary units stratigraphically higher with similar facies show no deformation.The studied interval lacks any evidence for possible trigger mechanisms intrinsic to the depositional environment, such as strong wave action, rapid sediment loading, evaporite dissolution and collapse, or desiccation, so ‘endogenic’ causes are ruled out. Thus, the deformation features are interpreted as seismites, and change in deformation style and inferred increase in intensity towards the south suggest that the earthquakes were sourced from the nearby Uinta Fault System. The 22 levels exhibiting seismites recognized in cores indicate earthquakes with minimum magnitudes between 6 and 7, minimum epicentral intensity (MCS) of ~9, and varying recurrence intervals in the seismic history of the Uinta Fault System, with a mean apparent recurrence period of ~8.1k.y. using average sedimentation rates and dated tuffs; in detail, however, there are two noticeably active periods followed by relative quiescence. The stratigraphic position of these deformed intervals also marks the transition between two distinct stages in lake evolution, from the balanced-filled Tipton Member to the overlying, underfilled Wilkins Peak Member. Thus, these seismites are evidence for regional-scale changes in lacustrine sedimentation of Eocene Lake Gosiute in response to syndepositional tectonic activity. Analysis of synsedimentary deformation features is, therefore, a promising yet under-utilized tool to trace the tectonic evolution of lacustrine deposits of the Green River Formation and other tectonically active marine and non-marine basins.

Mammals from the earliest Uintan (middle Eocene) Turtle Bluff Member, Bridger Formation, southwestern Wyoming, USA, Part 1: Primates and Rodentia

Mammals from the earliest Uintan (middle Eocene) Turtle Bluff Member, Bridger Formation, southwestern Wyoming, USA, Part 1: Primates and Rodentia

Credible regions for exceedance sets of geostatistical data

Identifying regions having large or unusual response in a spatial domain is frequently of interest in environmental and public health contexts. These regions having a large response are frequently called exceedance sets, exceedance regions, or excursion sets. We propose Bayesian methodology for constructing credible regions that either contain the exceedance sets or are contained within the exceedance sets with a specified level probability. The algorithms are simple to implement and use samples from the joint posterior predictive distribution of the process of interest. The R package ExceedanceTools implements the proposed methodology. We study the coverage properties of the methodology and also show that it has good coverage properties in practice. Simulation experiments demonstrate that the proposed method has good performance with respect to the empirical coverage and power. We apply this methodology to identify regions of high zinc concentration using soil samples collected in southwestern Wyoming. Copyright © 2015 John Wiley & Sons, Ltd.

Eocene Paleoseismic Record of the Green River Formation, Fossil Basin, Wyoming, U.S.A.: Implications of Synsedimentary Deformation Structures In Lacustrine Carbonate Mudstones

Abstract Laterally extensive intervals containing sedimentary deformation features are identified in outcrops of lacustrine deposits of the Eocene (∼ 52–51 Ma) Green River Formation in Fossil Basin, southwestern Wyoming. Fossil Basin is the smallest of the paleo-lakes in the Green River system and is located in the Sevier Fold and Thrust Belt, which was tectonically active during deposition. Deformation structures include convolute lamination, load structures, hybrid brittle–ductile features, sedimentary dikes, microfaults, fluid-escape features such as cusps and pipes, oil-shale breccias, and mass-transport deposits. In most cases these structures are hosted by finely laminated, variably organic-rich carbonate mudstones that accumulated in a low-energy profundal lacustrine environment. Deformed intervals range from a few centimeters to 5 m in thickness and are bound above and below by undeformed strata of the same facies, which demonstrates the early post-depositional timing of deformation. The distribution of these features indicates a primary control exerted by sediment rheology, resulting from variation in grain size, clay and organic content, and degree of lithification, which in turn were governed by the depositional environment and early diagenesis. Based on their morphological attributes, lateral extent, and recurrence at different stratigraphic levels, along with their sedimentary environment and the tectonic setting of the basin, the deformation structures are interpreted to be “seismites,” i.e., the result of stresses induced by syndepositional earthquakes, and other potential trigger agents are rejected. Moreover, stratigraphic relationships indicate that these small-scale deformation features as well as the mass-transport deposits, formed on a virtually flat lake floor, ruling out instability caused by the gravitational regime. Syndepositional deformation in Fossil Basin points to tectonic activity along the nearby Absaroka and/or Hogsback thrusts and related fault systems. Seismites point to possible tectonic forcing as a mechanism for changes in bathymetry and sedimentation in the Green River Formation and, consequently, demonstrate their potential for elucidating the tectonic history of other lacustrine and marine basins.

Greater Sage-Grouse and Range Management: Insights from a 25-Year Case Study in Utah and Wyoming

Conservation of sagebrush (Artemisia spp.) systems is one of the most difficult and pressing concerns in western North America. Sagebrush obligates, such as greater sage-grouse (Centrocercus urophasianus; hereafter sage-grouse), have experienced population declines as sagebrush systems have degraded. Science-based management is crucial to improve certainty in range management practices. Although large-scale implementation of management regimens within an experimental design is difficult, long-term case studies provide opportunities to improve learning and develop and refine hypotheses. We used 25 years of data across three large landscapes in northern Utah and southwestern Wyoming to assess sage-grouse population change and corresponding land management differences in a case study design. Sage-grouse lek counts at our Deseret Land and Livestock (DLL) study site increased relative to surrounding populations in correspondence with the implementation of small-acreage sagebrush treatments designed to reduce shrub cover and increase herbaceous understory within a prescriptive grazing management framework. The higher lek counts were sustained for nearly 15 years. However, with continued sagebrush treatments and the onset of adverse winter conditions, DLL lek counts declined to levels consistent with surrounding areas. During summer, DLL sage-grouse broods used plots of small, treated sagebrush mosaics more than untreated reference sites. We hypothesize that sagebrush treatments on DLL increased availability of grasses and forbs to sage-grouse, similar to other studies, but that cumulative annual reductions in sagebrush may have reduced availability of sagebrush cover for sage-grouse seasonal needs at DLL, especially when extreme winter weather occurred.

Sagebrush steppe recovery on 30–90‐year‐old abandoned oil and gas wells

Oil and natural gas extraction is rapidly expanding in semiarid intermountain big sagebrush ecosystems of the western USA. Formerly covering over 60 million ha, this ecosystem has lost almost half its area due to land use changes. In this study, we measured the natural recovery of the big sagebrush plant community across a chronosequence of 29 oil and gas well sites that were abandoned without reclamation between 1923 and 1980. We measured big sagebrush cover and density with strip transects inside and outside of the well sites, and we estimated big sagebrush biomass using both canopy measurements and allometric equations. Cover of other shrubs, grasses, and forbs was estimated with line transects inside and outside of well sites. We estimated that it takes at least 87 years for Wyoming big sagebrush cover to recover naturally, although big sagebrush density recovered in fewer than 70 years. Grasses and non‐sagebrush shrubs recovered rapidly, shown by the high cover of those groups in the youngest sites. We found none of the invasive plants that are common in disturbed big sagebrush communities in other parts of the big sagebrush range. The forbs that account for the largest portion of plant species richness in semiarid ecosystems and promote consumer diversity showed very little indication of recovery after 87 years. Our results suggest that reclamation efforts in disturbed big sagebrush plant communities in southwestern Wyoming should target big sagebrush and forbs.

Upper Cretaceous Sequence Stratigraphy of the Rock Springs Uplift, Wyoming

Three scales of sedimentary cyclicity are observed in the Campanian to Maastrichtian-aged strata of southwestern Wyoming based on sedimentary stacking patterns, facies successions, paleontological data and geometric criteria from outcrop, and subsurface data. The largest scale of sequence stratigraphic interpretation is of 10-15 million years duration per cycle and is designated as second order. Second-order cyclicity is represented by profound sequence boundaries and maximum-flooding surfaces that are related to regional tectono-subsidence drivers. The 2nd-order sequence boundaries at the base of the Ericson Formation (Moxa Unconformity) and the base of the Fort Union Formation (Laramide Unconformity) locally erode thousands of feet of section on discrete structural highs, but also show evidence of uplift on a broader scale. Both unconformities terminate long successions of marine shoreline progradation. Second-order maximum flooding surfaces are present within thick marine mudstone successions of the Baxter-Niobrara and Lewis formations. These intervals represent the deepest water deposits in the Upper Cretaceous and are associated with important regional seals and source rocks. The large-scale tectono-cyclicity is composed of an aggregate of smaller-scale, 3rd- and 4th-order sequences and their component systems tracts. In addition to the second-order sequences described above, third-order sequence boundaries are interpreted at the base of the Blair Formation, base of the Chimney Rock Member of the Rock Springs Formation, and at the base of the Canyon Creek Member of the Ericson Formation. Third-order maximum flooding surfaces are in the middle Blair Formation, middle Black Butte Member of the Rock Springs Formation, and in the upper part of the Rusty Member of the Ericson Formation. At least 7 additional 4th-order sequences can be interpreted within these successions. The higher-order cycles are shorter in duration and smaller in magnitude (i.e., thinner and with a smaller degree of change in environments or bathymetry within a cycle). The sequence stratigraphic interpretation approach is observationally based and consistent across these scales. However, finer-scale sequence stratigraphic interpretations, especially at the 4th-order scale, are subject to additional subjectivity. An important challenge is to separate apparent cyclicity related to factors such as local to regional shifting of depocenters (autocyclicity) from regionally correlative cyclicity (allocyclicity) within the high-frequency sequences. Examples of this are provided, most clearly for the lower portion of the Blair Formation. Such considerations are important economically, as this is the scale that controls sandstone reservoir and mudstone seal architecture within petroleum fields. Standard systems tracts criteria using parasequence stacking patterns are extended to non-marine strata by use of the degree of amalgamation (net/gross) of the fluvial sandstones. This approach is demonstrated to be plausible via physical ties to shoreline systems using regional correlations and paleontology, and via estimates of accommodation change from geohistory analysis.

Density of river otters (Lontra canadensis) in relation to energy development in the Green River Basin, Wyoming

Exploration and extraction of oil and natural gas have increased in recent years and are expected to expand in the future. Reduction in water quality from energy extraction may negatively affect water supply for agriculture and urban use within catchments as well as down river. We used non-invasive genetic techniques and capture–recapture modeling to estimate the abundance and density of North American river otters (Lontra canadensis), a sentinel species of aquatic ecosystems, in Southwestern Wyoming. While densities in two of three river reaches were similar to those reported in other freshwater systems in the western US (1.45–2.39km per otter), otters appeared to avoid areas near energy development. We found no strong difference in habitat variables, such as overstory cover, at the site or reach level. Also, fish abundance was similar among the three river reaches. Otter activity in our study area could have been affected by elevated levels of disturbance surrounding the industrial gas fields, and by potential surface water contamination as indicated by patterns in water conductivity. Continued monitoring of surface water quality in Southwestern Wyoming with the aid of continuously recording devices and sentinel species is warranted.

WELKOETOXYLON MULTISERIATUM: FOSSIL MORACEOUS WOOD FROM THE EOCENE GREEN RIVER FORMATION, WYOMING, U.S.A.

A silicified wood, Welkoetoxylon multiseriatum, gen. et sp. nov., is described from the late Early Eocene Green River Formation of southwestern Wyoming. The combination of features observed in W. multiseriatum, including latex tubes (laticifers) in the rays and abundant sheath cells, indicates affinities with the Moraceae. This is the first report of fossil moraceous wood from the Eocene of the western interior of the U.S.A. and it provides reliable evidence for the Paleogene occurrence of Moraceae in this region. The indistinct growth rings of this fossil indicate this tree did not experience a distinct dormant season.

Forecasting sagebrush ecosystem components and greater sage-grouse habitat for 2050: Learning from past climate patterns and Landsat imagery to predict the future

Sagebrush (Artemisia spp.) ecosystems constitute the largest single North American shrub ecosystem and provide vital ecological, hydrological, biological, agricultural, and recreational ecosystem services. Disturbances have altered and reduced this ecosystem historically, but climate change may ultimately represent the greatest future risk. Improved ways to quantify, monitor, and predict climate-driven gradual change in this ecosystem is vital to its future management. We examined the annual change of Daymet precipitation (daily gridded climate data) and five remote sensing ecosystem sagebrush vegetation and soil components (bare ground, herbaceous, litter, sagebrush, and shrub) from 1984 to 2011 in southwestern Wyoming. Bare ground displayed an increasing trend in abundance over time, and herbaceous, litter, shrub, and sagebrush showed a decreasing trend. Total precipitation amounts show a downward trend during the same period. We established statistically significant correlations between each sagebrush component and historical precipitation records using a simple least squares linear regression. Using the historical relationship between sagebrush component abundance and precipitation in a linear model, we forecasted the abundance of the sagebrush components in 2050 using Intergovernmental Panel on Climate Change (IPCC) precipitation scenarios A1B and A2. Bare ground was the only component that increased under both future scenarios, with a net increase of 48.98km2 (1.1%) across the study area under the A1B scenario and 41.15km2 (0.9%) under the A2 scenario. The remaining components decreased under both future scenarios: litter had the highest net reductions with 49.82km2 (4.1%) under A1B and 50.8km2 (4.2%) under A2, and herbaceous had the smallest net reductions with 39.95km2 (3.8%) under A1B and 40.59km2 (3.3%) under A2. We applied the 2050 forecast sagebrush component values to contemporary (circa 2006) greater sage-grouse (Centrocercus urophasianus) habitat models to evaluate the effects of potential climate-induced habitat change. Under the 2050 IPCC A1B scenario, 11.6% of currently identified nesting habitat was lost, and 0.002% of new potential habitat was gained, with 4% of summer habitat lost and 0.039% gained. Our results demonstrate the successful ability of remote sensing based sagebrush components, when coupled with precipitation, to forecast future component response using IPCC precipitation scenarios. Our approach also enables future quantification of greater sage-grouse habitat under different precipitation scenarios, and provides additional capability to identify regional precipitation influence on sagebrush component response.

Winter habitat use of greater sage‐grouse relative to activity levels at natural gas well pads

ABSTRACTEnergy development in western North America has been shown to negatively influence greater sage‐grouse (Centrocercus urophasianus) populations. No effective methods of reducing on‐site impacts of energy development to greater sage‐grouse are known. We investigated greater sage‐grouse use of wintering habitats relative to distances to infrastructure, densities of infrastructure, and activity levels associated with infrastructure of a natural gas field over 5 years in southwestern Wyoming. We compared year‐long drilling locations, locations of conventional well pads, locations of well pads with off‐site condensate and produced water gathering systems (LGS), and plowed main haul roads to the number of and time associated with greater sage‐grouse visits to continually monitored, distinct patches of habitat. Liquid gathering systems reduced human activity levels at producing well pads approximately 53%. We used data loggers to monitor distinct patches of habitat throughout the 2005–2006 to 2009–2010 winters and used the number of times and the amount of time individuals from a sample of greater sage‐grouse (n = 236) were detected at data logger stations to model frequency and time of occurrence as functions of anthropogenic and habitat variables. Greater sage‐grouse avoided suitable winter habitats in areas with high well pad densities regardless of differences in activity levels associated with well pads. Our results further suggested that greater sage‐grouse avoidance of conventional well pads was stronger than LGS well pads. We found relatively consistent positive relationships between distance to infrastructure with high levels of human activity and average hours greater sage‐grouse spent in an area. Greater sage‐grouse avoidance of natural gas field infrastructure during the winter may be explained mechanistically as movements of individuals from areas close to high levels of activity—movements that may occur at the time human activity is experienced—followed by a lack of movement back into these areas. Minimizing the densities of well pads may reduce on‐site impacts of energy development on wintering greater sage‐grouse. Our study, additionally, indicated that reducing anthropogenic activity levels associated with energy developments may reduce the temporal scale of indirect greater sage‐grouse winter habitat loss. © 2015 The Wildlife Society.

GIS-based geospatial infrastructure of water resource assessment for supporting oil shale development in Piceance Basin of Northwestern Colorado

Oil shale deposits of the Green River Formation (GRF) in Northwestern Colorado, Southwestern Wyoming, and Northeastern Utah may become one of the first oil shale deposits to be developed in the U.S. because of their richness, accessibility, and extensive prior characterization. Oil shale is an organic-rich fine-grained sedimentary rock that contains significant amounts of kerogen from which liquid hydrocarbons can be produced. Water is needed to retort or extract oil shale at an approximate rate of three volumes of water for every volume of oil produced. Concerns have been raised over the demand and availability of water to produce oil shale, particularly in semiarid regions where water consumption must be limited and optimized to meet demands from other sectors. The economic benefit of oil shale development in this region may have tradeoffs within the local and regional environment. Due to these potential environmental impacts of oil shale development, water usage issues need to be further studied. A basin-wide baseline for oil shale and water resource data is the foundation of the study. This paper focuses on the design and construction of a centralized geospatial infrastructure for managing a large amount of oil shale and water resource related baseline data, and for setting up the frameworks for analytical and numerical models including but not limited to three-dimensional (3D) geologic, energy resource development systems, and surface water models. Such a centralized geospatial infrastructure made it possible to directly generate model inputs from the same database and to indirectly couple the different models through inputs/outputs. Thus ensures consistency of analyses conducted by researchers from different institutions, and help decision makers to balance water budget based on the spatial distribution of the oil shale and water resources, and the spatial variations of geologic, topographic, and hydrogeological characterization of the basin. This endeavor encountered many technical challenging and has not been done in the past for any oil shale basin. The database built during this study remains valuable for any other future studies involving oil shale and water resource management in the Piceance Basin. The methodology applied in the development of the GIS based geospatial infrastructure can be readily adapted for other professionals to develop database structure for other similar basins.

Aceroryctes dulcis, a new palaeoryctid (Mammalia, Eutheria) from the early Eocene of the Wasatch Formation of southwestern Wyoming, USA

The Palaeoryctidae are a group of small-bodied, likely insectivorous mammals known principally from the Paleocene and early Eocene (from approximately 65 to 53 Ma) of North America. Here we report on a new palaeoryctid from the early Eocene (early Wasatchian (Wa3) North American Land Mammal Age) Main Body of the Wasatch Formation, Washakie Basin, near Bitter Creek station in southwestern Wyoming, USA. Acerorcytes dulcis gen. et sp. nov. is unique among palaeoryctids in having a double-rooted P2 with a small anterior cusp, P3 with pronounced para- and metastylar cusps and a reduced but conspicuous metacone, P4 with a weakly developed metacone and an anteroposteriorly compressed protocone, and M1-2 with deep ectoflexus and a sharp metastylar blade. A phylogenetic analysis based on 32 dental characters of the nine known North American palaeoryctid species, including Aceroryctes dulcis, recovered eight equally parsimonious cladograms. Similar to prior studies, the analysis suggests that the genus Palaeoryctes is non-monophyletic, with Palaeoryctes cruoris and Aaptoryctes ivyi closely related. Aceroryctes dulcis is grouped with Ottoryctes winkleri and positioned in a more inclusive clade with Eoryctes melanus; the remaining palaeoryctid taxa, including Lainoryctes youzwyshyni, are part of an unresolved polytomy. These new findings indicate that early Eocene palaeoryctids were more diverse than previously thought, with genus richness during the early Eocene at least as great as that during the middle Paleocene.

Fluvial deposition during transition from flexural to dynamic subsidence in the Cordilleran foreland basin: Ericson Formation, Western Wyoming, USA

AbstractThe Ericson Formation was deposited in the distal foredeep of the Cordilleran foreland basin during Campanian time. Isopach data show that it records early dynamic subsidence and the onset of basin partitioning by Laramide uplifts. The Ericson Formation is well exposed around the Rock Springs uplift, a Laramide structural dome in southwestern Wyoming; the formation is thin, regionally extensive, and does not display the wedge‐shaped geometry typical of foredeep deposits. Sedimentation in this area was controlled both by activity in the thrust belt and by intraforeland tectonics. The Ericson Formation is ideally situated both spatially and temporally to study the transition from Sevier to Laramide (thin‐ to thick‐skinned) deformation which corresponded to the shift from flexural to dynamic subsidence and the demise of the Cretaceous foreland basin system. We establish the depositional age of the Ericson Formation as ca. 74 Ma through detrital zircon U–Pb analysis. Palaeocurrent data show a generally southeastward transport direction, but northward indicators near Flaming Gorge Reservoir suggest that the intraforeland Uinta uplift was rising and shedding sediment northward by late Campanian time. Petrographic data and detrital zircon U–Pb ages indicate that Ericson sediment was derived from erosion of Proterozoic quartzites and Palaeozoic and Mesozoic quartzose sandstones in the Sevier thrust belt to the west. The new data place temporal and geographic constraints on attempts to produce geodynamic models linking flat‐slab subduction of the oceanic Farallon plate to the onset of the Laramide orogenic event.

Predicting Occupancy for Pygmy Rabbits in Wyoming: An Independent Evaluation of Two Species Distribution Models

Abstract Species distribution models are an important component of natural-resource conservation planning efforts. Independent, external evaluation of their accuracy is important before they are used in management contexts. We evaluated the classification accuracy of two species distribution models designed to predict the distribution of pygmy rabbit Brachylagus idahoensis habitat in southwestern Wyoming, USA. The Nature Conservancy model was deductive and based on published information and expert opinion, whereas the Wyoming Natural Diversity Database model was statistically derived using historical observation data. We randomly selected 187 evaluation survey points throughout southwestern Wyoming in areas predicted to be habitat and areas predicted to be nonhabitat for each model. The Nature Conservancy model correctly classified 39 of 77 (50.6%) unoccupied evaluation plots and 65 of 88 (73.9%) occupied plots for an overall classification success of 63.3%. The Wyoming Natural Diversity Database model correctly classified 53 of 95 (55.8%) unoccupied plots and 59 of 88 (67.0%) occupied plots for an overall classification success of 61.2%. Based on 95% asymptotic confidence intervals, classification success of the two models did not differ. The models jointly classified 10.8% of the area as habitat and 47.4% of the area as nonhabitat, but were discordant in classifying the remaining 41.9% of the area. To evaluate how anthropogenic development affected model predictive success, we surveyed 120 additional plots among three density levels of gas-field road networks. Classification success declined sharply for both models as road-density level increased beyond 5 km of roads per km-squared area. Both models were more effective at predicting habitat than nonhabitat in relatively undeveloped areas, and neither was effective at accounting for the effects of gas-energy-development road networks. Resource managers who wish to know the amount of pygmy rabbit habitat present in an area or wanting to direct gas-drilling efforts away from pygmy rabbit habitat may want to consider both models in an ensemble manner, where more confidence is placed in mapped areas (i.e., pixels) for which both models agree than for areas where there is model disagreement.

Use of seasonally available habitat by northern leatherside in Wyoming

To evaluate use of habitat by northern leatherside (Lepidomeda copei), intermittent reaches of streams adjacent to streams containing northern leatherside were electrofished. Northern leatherside were collected from two of five intermittent streams sampled in southwestern Wyoming. The opportunistic use of seasonally available habitats by northern leatherside might be reflective of spawning movements and is consistent with its evolutionary history.

Human Infrastructure and Invasive Plant Occurrence Across Rangelands of Southwestern Wyoming, USA

Although human influence across rural landscapes is often discussed, interactions between the native, natural systems and human activities are challenging to measure explicitly. We assessed the distribution of introduced, invasive species as related to anthropogenic infrastructure and environmental conditions across southwestern Wyoming. to discern direct correlations as well as covariate influences between land use, land cover, and abundance of invasive plants, and assess the supposition that these features affect surrounding rangeland conditions. Our sample units were 1 000 m long and extended outward from target features, which included roads, oil and gas well pads, pipelines, power lines, and featureless background sites. Sample sites were distributed across the region using a stratified, random design with a frame that represented features and land-use intensity. In addition to land-use gradients, we captured a representative, but limited, range of variability in climate, soils, geology, topography, and dominant vegetation. Several of these variables proved significant, in conjunction with distance from anthropogenic features, in regression models of invasive plant abundance. We used general linear models to demonstrate and compare associations between invasive plant frequency and Euclidian distance from features, natural logarithm transformed distances (log-linear), and environmental variables which were presented as potential covariates. We expected a steep curvilinear (log or exponential) decline trending towards an asymptote along the axis representing high abundance near features with rapid decrease beyond approximately 50–100 m. Some of the associations we document exhibit this pattern, but we also found some invasive plant distributions that extended beyond our expectations, suggesting a broader distribution than anticipated. Our results provide details that can inform local efforts for management and control of invasive species, and they provide evidence of the different associations between natural patterns and human land use exhibited by nonnative species in this rural setting, such as the indirect effects of humans beyond impact areas.

Additions to the latest Paleocene Buckman Hollow local fauna, Chappo Member of the Wasatch Formation, Lincoln County, southwestern Wyoming

Additions to the latest Paleocene Buckman Hollow local fauna, Chappo Member of the Wasatch Formation, Lincoln County, southwestern Wyoming