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Research about Mojave Desert

Source-linked reports with geographic coverage including Mojave Desert.

At least 37 records · Page 2Linked to original sources
USGS2021

Urbanization’s influence on the distribution of mange in a carnivore revealed with multistate occupancy models

Increasing urbanization and use of urban areas by synanthropic wildlife has increased human and domestic animal exposure to zoonotic diseases and exacerbated epizootics within wildlife populations. Consequently, there is a need to improve wildlife disease surveillance programs to rapidly detect outbreaks and refine inferences regarding spatiotemporal disease dynamics. Multistate occupancy models can address potential shortcomings in surveillance programs by accounting for imperfect detection and the misclassification of disease states. We used these models to explore the relationship between urbanization, slope, and the spatial distribution of sarcoptic mange in coyotes ( Canis latrans ) inhabiting Fort Irwin, California, USA. We deployed remote cameras across 180 sites within the desert surrounding the populated garrison and classified sites by mange presence or absence depending on whether a symptomatic or asymptomatic coyote was photographed. Coyotes selected flatter sites closer to the urban area with a high probability of use (0.845, 95% credible interval (CRI): 0.728, 0.944); site use decreased as the distance to urban areas increased (standardized β ^ "> β ˆ β^ = − 1.354, 95% CRI − 2.423, − 0.619). The probability of correctly classifying mange presence at a site also decreased further from the urban area and was probably related to the severity of mange infection. Severely infected coyotes, which were more readily identified as symptomatic, resided closer to the urban area and were most likely dependent on urban resources for survival; urban resources probably contributed to sustaining the disease. Multistate occupancy models represent a flexible framework for estimating the occurrence and spatial extent of observable infectious diseases, which can improve wildlife disease surveillance programs.

California↗
USGS2021

Harnessing landscape genomics to identify future climate resilient genotypes in a desert annual

Local adaptation features critically in shaping species responses to changing environments, complicating efforts to revegetate degraded areas. Rapid climate change poses an additional challenge that could reduce fitness of even locally sourced seeds in restoration. Predictive restoration strategies that apply seeds with favourable adaptations to future climate may promote long‐term resilience. Landscape genomics is increasingly used to assess spatial patterns in local adaption and may represent a cost‐efficient approach for identifying future‐adapted genotypes. To demonstrate such an approach, we genotyped 760 plants from 64 Mojave Desert populations of the desert annual Plantago ovata . Genome scans on 5,960 SNPs identified 184 potentially adaptive loci related to climate and satellite vegetation metrics. Causal modelling indicated that variation in potentially adaptive loci was not confounded by isolation by distance or isolation by habitat resistance. A generalized dissimilarity model (GDM) attributed spatial turnover in potentially adaptive loci to temperature, precipitation and NDVI amplitude, a measure of vegetation green‐up potential. By integrating a species distribution model (SDM), we find evidence that summer maximum temperature may both constrain the range of P. ovata and drive adaptive divergence in populations exposed to higher temperatures. Within the species’ current range, warm‐adapted genotypes are predicted to experience a fivefold expansion in climate niche by midcentury and could harbour key adaptations to cope with future climate. We recommend eight seed transfer zones and project each zone into its relative position in future climate. Prioritizing seed collection efforts on genotypes with expanding future habitat represents a promising strategy for restoration practitioners to address rapidly changing climates.

California, Nevada↗
USGS2021

Borreliosis transmission from ticks to humans associated with desert tortoise burrows: Examples of tick-borne relapsing fever in the Mojave Desert

Ticks transmit pathogens and parasitize wildlife in turn causing zoonotic diseases in many ecosystems. Argasid ticks, such as Ornithodoros spp., harbor and transmit Borrelia spp., resulting in tick-borne relapsing fever (TBRF) in people. In the western United States, TBRF is typically associated with the bite of an infected Ornithodoros hermsi tick found in habitats at high elevations (>1500 ft). This report describes the first TBRF cases in people in the Mojave Desert (Clark County, NV). Individuals documented in these case studies were exposed to Ornithodoros ticks during excavation of soil burrows associated with Mojave Desert tortoises ( Gopherus agassizii ), with bacteria from one of the human case's blood sample genetically matching to Borrelia turicatae as determined by quantitative PCR and sequencing. Our findings should serve as a precaution to individuals working with tortoises or animal burrows, or those in contact with Ornithodoros ticks in this region.

California, Nevada↗
USGS2021

Gopherus agassizii

A provisional Red List Assessment of the widespread Desert Tortoise, Gopherus agassizii ( sensu lato ), was performed at a Desert Tortoise Council workshop in 2010 and updated by the IUCN Tortoise and Freshwater Turtle Specialist Group (TFTSG) in 2011, at which time the Mojave Desert subpopulation, now considered G. agassizii ( sensu stricto ) following taxonomic analysis and splitting into three separate species ( G. agassizii , G. morafkai , and G. evgoodei ), was assessed as Critically Endangered A2bce+A4bce based on population reduction (decreasing density), habit loss of over 80% over three generations (90 years), including past reductions and predicted future declines, as well as the effects of disease (upper respiratory tract disease / mycoplasmosis). Gopherus agassizii ( sensu stricto ) comprises tortoises in the most well-studied 30% of the larger range; this portion of the original range has seen the most human impacts and is where the largest past population losses had been documented. A recent rigorous range-wide population reassessment of G. agassizii ( sensu stricto ) has demonstrated continued adult population and density declines of about 90% over three generations (two in the past and one ongoing) in four of the five G. agassizii recovery units and inadequate recruitment with decreasing percentages of juveniles in all five recovery units. As such, we reaffirm the prior assessment of the taxonomically restricted Mojave Desert Tortoise, G. agassizii , as Critically Endangered, and add criterion “a” for direct population observations: CR A2abce+A4abce. The previously defined widespread species G. agassizii ( sensu lato ) was last assessed as Vulnerable on the IUCN Red List in 1996; a separate assessment currently in progress by the TFTSG for the Sonoran Desert Tortoise, G. morafkai (previously considered part of G. agassizii ) has provisionally assessed that species as Vulnerable.

Arizona, California, Nevada, Utah↗
USGS2021

Priority species lists to restore desert tortoise and pollinator habitats in Mojave Desert shrublands

Mojave Desert shrublands are home to unique plants and wildlife and are experiencing rapid habitat change due to unprecedented large-scale disturbances; yet, established practices to effectively restore disturbed landscapes are not well developed. A priority species list of native plant taxa was developed to guide seed collectors, commercial growers, resource managers, and restoration practitioners in support of the Bureau of Land Management's Mojave Desert Native Plant Program. We identify focal plant taxa that are important for habitats of the threatened Mojave desert tortoise ( Gopherus agassizii ), a widely distributed herbivore in low and middle elevations, and pollinator taxa, including mostly Lepidopterans and Apoidean bees, some of whose populations are in decline. We identified 201 unique plant taxa in the diets of tortoises, and 49 taxa that provide thermal cover for tortoises with some overlapping taxa that provide both diet and cover. We discuss 134 native pollinators associated with plants used for nectaring, larval hosts, or cover and nesting materials. Detailed plant species accounts describing the status-of-knowledge for 57 plant taxonomic groups including detailed information on life history, ecology, and pollinator syndrome relevant to restoration success, methods of seed harvesting, propagation, and historical use in restoration. Our approach for developing a priority plant species list for the Mojave Desert provides a data-guided listing of species for restoration practitioners and identifies knowledge gaps for future investigation.

California, Nevada↗
USGS2020

Genes in space: What Mojave desert tortoise genetics can tell us about landscape connectivity

Habitat loss and fragmentation in the Mojave Desert have been increasing, which can create barriers to movement and gene flow leading to decreased populations of native species. Disturbance and degradation of Mojave desert tortoise habitat includes linear features (e.g. highways, railways, and a network of dirt roads), urbanized areas, and their associated infrastructure, mining activities, energy distribution systems, and most recently, utility-scale solar facilities. To evaluate the spatial genetic structure of tortoises in an area experiencing rapid habitat loss, we conducted field surveys from 2015-2017 and genotyped 299 tortoises at 20 microsatellite loci within and around Ivanpah Valley along the California/Nevada border. We used a Bayesian clustering analysis to examine population genetic structure across valley and mountain pass habitat. Spatial principal components analysis was included to further investigate population genetic structure with isolation-by-distance. To explicitly incorporate landscape features (e.g. habitat and anthropogenic linear barriers) we used maximum likelihood population effects. We assessed recent gene flow on the landscape through maximum likelihood pedigree analyses of relatedness. We detected three to four genetic clusters with high levels of admixture that generally corresponded to three valleys separated by mountain ranges, and a genetically distinguishable population in one mountain pass. Pedigree analyses showed second order relationships up to 60 km apart suggesting a greater range of interactions and inter-relatedness between individuals than previously suspected. Our results support historical gene flow with isolation-by-resistance, and reveal a genetic signal indicative of reduction in genetic connectivity across two parallel linear features (a railway and a highway). This work demonstrates the value of protecting connected tracts of functional habitat and the importance of connectivity research in conservation.

California, Nevada↗
USGS2020

Development of a genotyping protocol for Mojave desert tortoise scat

Noninvasive fecal genotyping can be a useful tool for population monitoring of elusive species. We tested extraction protocols on scat samples from the threatened Mojave Desert tortoise, Gopherus agassizii, to evaluate whether scat-based mark–recapture and population genetic monitoring studies are feasible.We extracted DNA from G. agassizii scat samples collected in California and Nevada using several extraction protocols and evaluated the reliability of resulting genotypes using quality scores, maximum likelihood reliability estimates, and paired scat and blood genotypes from the same individuals. Finally, we assessed probabilities of identity and sibship, and locus amplification quality, and calculated genotyping error rates for 19 microsatellite loci to determine the best set of loci to use with G. agassizii scat extractions. We found that genotype quality depended more on the sample quality than on the extraction method, and that the Qiagen DNeasy Plant Mini extraction kit is an efficient method for extracting tortoise DNA from tortoise scat. We identified 6 G. agassizii microsatellite loci that can be used to generate a unique molecular tag for individual tortoises. We characterized the reliability of an additional 13 microsatellite loci for use in population genetic analyses where additional power at the expense of some increase in error may be advantageous. As proof of concept, with very low error rates, we matched 3 opportunistically collected scat samples to blood genotypes from animals captured during population surveys within the study area and discovered at least 3 new individuals, even after 2 yrs of extensive survey work. These results suggest that genotyping of field-collected scat can complement existing methods used in long-term demographic and movement studies of G. agassizii and other, closely related, tortoise species.

California↗
USGS2020

Context-dependent effects of livestock grazing in deserts of western North America

This chapter provides a general review of grazing disturbance by large mammalian grazers and the role of ecological context in moderating its effects, with emphasis on North American deserts. It discusses the ecological consequences of cessation of livestock grazing and present a case study from the Mojave Desert, United States of America. A primary effect of grazing is selective removal and ingestion of herbaceous plants, in contrast to removal of woody biomass from woody plants by browsing herbivores. The consequences of grazing–and resilience of a system to grazing disturbance–are highly context-dependent and vary across rangelands globally. Synergistic interactions between soil depth and plant structural properties, such as rooting depth and water-use efficiency, also influence plant access to water, and therefore moderate plant responses to drought and resilience to grazing. In some ecosystems, livestock grazing constitutes a novel or intensified disturbance. Application of the Intermediate Disturbance Hypothesis to grazing disturbance has been relatively infrequently tested relative to other ecological disturbances.

California, Nevada↗
USGS2019

Effects of invasive plants on fire regimes and postfire vegetation diversity in an arid ecosystem

We assessed the impacts of co‐occurring invasive plant species on fire regimes and postfire native communities in the Mojave Desert, western USA. We analyzed the distribution and co‐occurrence patterns of three invasive annual grasses (Bromus rubens, Bromus tectorum, and Schismus spp.) known to alter fuel conditions and community structure, and an invasive forb (Erodium cicutarium) which dominates postfire sites. We developed species distribution models (SDMs) for each of the four taxa and analyzed field plot data to assess the relationship between invasives and fire frequency, years postfire, and the impacts on postfire native herbaceous diversity. Most of the Mojave Desert is highly suitable for at least one of the four invasive species, and 76% of the ecoregion is predicted to have high or very high suitability for the joint occurrence of B. rubens and B. tectorum and 42% high or very high suitability for the joint occurrence of the two Bromus species and E. cicutarium. Analysis of cover from plot data indicated two or more of the species occurred in 77% of the plots, with their cover doubling with each additional species. We found invasive cover in burned plots increased for the first 20 years postfire and recorded two to five times more cover in burned than unburned plots. Analysis also indicated that native species diversity and evenness as negatively associated with higher levels of relative cover of the four invasive taxa. Our findings revealed overlapping distributions of the four invasives; a strong relationship between the invasives and fire frequency; and significant negative impacts of invasives on native herbaceous diversity in the Mojave. This suggests predicting the distributions of co‐occurring invasive species, especially transformer species, will provide a better understanding of where native‐dominated communities are most vulnerable to transformations following fire or other disturbances.

California, Nevada↗
USGS2019

A range-wide model of contemporary, omnidirectional connectivity for the threatened Mojave desert tortoise

As habitat destruction leads to species extinctions globally, conservation planning that accounts for population-level connectivity and gene flow is an urgent priority. Models that only approximate habitat potential are incomplete because areas of high habitat potential may be isolated, whereas intermixed areas of lower habitat potential may still be critical for maintaining connectivity between and among populations. We developed a range-wide, omnidirectional (‘coreless’) connectivity model and map for the threatened Mojave desert tortoise at a high spatial resolution (30 m), based on empirical movement data and a circuit-theoretic approach to estimating connectivity. Specifically, we first estimated habitat potential (i.e., quality) for tortoise movement (as distinct from habitat potential more generally) across its range using hypotheses based on the published literature, linear mixed models, multiple environmental factors derived from remotely sensed data, and recent solar and wind development footprints. The resultant raster output was used to represent landscape conductance in a circuit-theoretic model of connectivity, which relates the flow of electrical current through a circuit to the movement of tortoises through the landscape. We then modeled potential connectivity across the range of the tortoise using Circuitscape software and the Julia numerical programming language. Intermediate distances from minor roads, intermediate values of annual average maximum temperature, and increasing density of desert washes were among the strongest predictors of movement habitat quality. There was also strong evidence for increased habitat quality for movement with increasing amounts of vegetation cover. The resulting connectivity model and map was determined to accurately reflect important areas for tortoise movement, but we encourage others to do their own evaluation of the model within local areas of interest and as more data become available. Accordingly, the map can provide an important component to improve management decisions that have the potential to influence the conservation of connected desert tortoise populations throughout the range.

California↗
USGS2019

Spatially consistent high-resolution land surface temperature mosaics for thermophysical mapping of the Mojave Desert

Daytime and nighttime thermal infrared observations acquired by the ASTER and MODIS instruments onboard the NASA Terra spacecraft have produced a dataset that can be used to map thermophysical properties across large regions, which have implications on surface processes, thermal environments and habitat suitability for desert species. ASTER scenes acquired between 2004 and 2012 are combined using new mosaicking and data-fusion techniques to produce a map of daytime and nighttime land surface temperature with coverage exclusive of the effects of clouds and weather. These data are combined with Landsat 7 visible imagery to generate a consistent map of apparent thermal inertia (ATI), which is related to the presence of exposed bedrock, rocks, fine-grained sediments and water on the surface. The resulting datasets are compared to known geomorphic units and surface types to generate an interpreted mechanical composition map of the entire Mojave Desert at 100 m per pixel that is most sensitive to large clast size distinctions in grain size distribution.

ARizone, California, Nevada, Utah↗
USGS2019

Ten-million years of activity within the Eastern California Shear Zone from U-Pb dating of fault-zone opal

Reconstructions of long-term fault activity are essential for understanding both the mechanisms controlling fault behavior and accurate earthquake hazard assessments. Increasing evidence for temporal variations in strain accumulation suggests non-uniform strain rates over a range of historic to geologic timescales. The paucity of long-term records of fault activity has limited our ability to resolve these variations. We present a method for constraining long-term fault activity based on U-Pb dating of fault-related opal from secondary fault segments within the Eastern California Shear Zone (ECSZ). The presence of sheared and breccia-cemented opaline silica within well-exposed faults at near-surface conditions suggest that opal formation is associated with high-magnitude earthquakes capable of surface rupture (>6 M). Temporal constraints from sheared syntectonic opal (n=74) on related secondary faults from this study provide new insights on the timing of fault initiation, reactivation, and longevity. The oldest dates obtained indicate that ECSZ activity commenced at or before 10 Ma. Multiple deformation events dated within a single structure on episodically deposited and sheared opal (up to six generations), demonstrate that fault reactivation occurred over 105 year timescales (0.7-0.1 Ma). Relative probabilities of dated deformation events can be used to evaluate changes in fault activity in the past 2.5 Ma (n=60). This analysis indicates enhanced fault activity starting at 2 Ma and peaking around 1 Ma, possibly due to fault-interactions and distribution of deformation between the ECSZ and the San Andreas Fault.

California↗
USGS2019

Selected trace-elements in alluvium and rocks, western Mojave Desert, southern California

Concentrations of twenty-seven elements, including naturally-occurring water-quality contaminants arsenic, chromium, and uranium, were measured in 217 samples of alluvium and rock from the western Mojave Desert, southern California, using portable (pXRF) and laboratory (LXRF) X-ray fluorescence. Comparison of measurements with NIST-traceable standards was good, although pXRF overestimated iron compared to LXRF. Results suggest pXRF survey data are sufficiently accurate to assess regional geochemical differences in geologic-source terrains. Principal component analysis showed rubidium and potassium were associated with alluvium eroded from felsic terrain, while iron, copper, chromium, and to a lesser extent titanium, manganese, and nickel were associated with alluvium eroded from mafic terrain. Zinc, vanadium, and arsenic were associated with alluvium eroded from hydrothermal terrain. Elemental assemblages associated with different source terrains were traced spatially to identify the source and composition of alluvium composing aquifers pumped for water supply. Changes in geologic source terrain to the Mojave River, associated with movement along the San Andreas Fault over the past one to five million years, reduced the mafic fraction and increased the felsic fraction of alluvium deposited to the regionally important floodplain aquifer along the Mojave River—lowering chromium concentrations in alluvium through geologic time. Comparison of pXRF and sequential extraction data from 40 samples showed arsenic and uranium were more abundant on the surfaces of mineral grains, while chromium and vanadium remained mostly within unweathered mineral grains—suggesting arsenic and uranium may be more readily mobilized into groundwater with changes in pH, redox, or ionic strength than chromium or vanadium.

California↗
USGS2019

Strike-slip fault interactions at Ivanpah Valley, California and Nevada

Ivanpah Valley is flanked by high mountain ranges, and represents one of the most imposing valleys of the eastern Mojave Desert. Its sinuous shape implies a complex origin as does the fact that it is not bordered by prominent range-front normal faults like valleys of the Basin and Range Province. In Addition, its deepest sedimentary basin is restricted to a small part of the valley near Nipton that does not coincide with the lowest part of the valley at Ivanpah Lake. The deep basin was caused by pull-apart at the intersection of two major strike-slip faults, the Stateline and Nipton faults. The northern part of the valley, in Nevada, probably resulted from normal faulting, and much of the normal faulting may have predated the strike-slip faulting. The southern valley, in California, is underlain by bedrock at shallow depths and is of uncertain origin. The dextral Stateline fault terminates at the sinistral Nipton fault, indicating that eastern California shear zone tectonics in this area consists of interwoven synthetic and antithetic faults, rather than through-going strike slip faults of a single orientation.

California, Nevada↗
USGS2018

Desert wetlands record hydrologic variability within the Younger Dryas chronozone, Mojave Desert, USA

One of the enduring questions in the field of paleohydrology is how quickly desert wetland ecosystems responded to past episodes of abrupt climate change. Recent investigations in the Las Vegas Valley of southern Nevada have revealed that wetlands expanded and contracted on millennial and sub-millennial timescales in response to changes in climate during the late Quaternary. Here, we evaluate geologic evidence from multiple localities in the Mojave Desert and southern Great Basin that suggests the response of wetland systems to climate change is even faster, occurring at centennial, and possibly decadal, timescales. Paleowetland deposits at Dove Springs Wash, Mesquite Springs, and Little Dixie Wash, California, contain evidence of multiple wet and dry cycles in the form of organic-rich black mats, representing periods of past groundwater discharge and wet conditions, interbedded with colluvial, alluvial, and aeolian sediments, each representing dry conditions. Many of these wet-dry cycles date to within the Younger Dryas (YD) chronozone (12.9–11.7 ka), marking the first time intra -YD hydrologic variability has been documented in paleowetland deposits. Our results illustrate that desert wetland ecosystems are exceptionally sensitive to climate change and respond to climatic perturbations on timescales that are relevant to human society.

Arizona, California, Nevada↗
USGS2018

Against the current— The Mojave River from sink to source: The 2018 Desert Symposium field trip road log

The Mojave River evolved over the past few million years by “fill and spill” from upper basins near its source in the Transverse Ranges to lower basins. Each newly “spilled into” basin in the series? sustained a long-lived lake but gradually filled with Mojave River sediment, leading to spill to a yet lower elevation? basin. The Mojave River currently terminates at Silver Lake, near Baker, CA, but previously overflowed this terminus onward to Lake Manly in Death Valley during the last glacial cycle. The river’s origin and evolution are intricately interwoven with tectonic, climatic, and geomorphic processes through time, beginning with San Andreas fault interactions that created a mountain range across a former externally draining river. We will see and discuss the Mojave River’s predecessor streams and basins, its evolution as it lengthened to reach the central Mojave Desert, local and regional tectonic controls, groundwater flow, flood history, and support of isolated perennial stream reaches that host endemic species. In association with these subjects are supporting studies such as paleoclimate records, location and timing for groundwater and wetlands in the central Mojave Desert, and effects of modern water usage. The trip introduces new findings for the groundwater basin of Hinkley Valley, including an ongoing remediation project that provides a wealth of information on past and present river flow and associated development of the groundwater system.

California↗