Mojave Desert Of California Research Articles

Of Mojave milkweed and mirrors: The population genomic structure of a species impacted by solar energy development

AbstractA rapid renewable energy transition has facilitated the development of large, ground‐mounted solar energy facilities worldwide. Deserts, and other sensitive aridland ecosystems, are the second most common land‐cover type for solar energy development globally. Thus, it is necessary to understand existing diversity within environmentally sensitive desert plant populations to understand spatiotemporal effects of solar energy siting and design. Overall, few population genomic studies of desert plants exist, and much of their biology is unknown. To help fill this knowledge gap, we sampled Mojave milkweed (Asclepias nyctaginifolia) in and around the Ivanpah Solar Electric Generating Station (ISEGS) in the Mojave Desert of California to understand the species' population structure, standing genetic variation, and how that intersects with solar development. We performed Restriction‐site Associated Sequencing (RADseq) and discovered 9942 single nucleotide polymorphisms (SNPs). Using these data, we found clear population structure over small spatial scales, suggesting each site sampled comprised a genetically distinct population of Mojave milkweed. While mowing, in lieu of blading, the vegetation across the solar energy facility's footprint prevented the immediate loss of the ISEGS Mojave milkweed population, we show that the effects of land‐cover change, especially those impacting desert washes, may impact long‐term genetic diversity and persistence. Potential implications of this include a risk of overall loss of genetic diversity, or even hastened extirpation. These findings highlight the need to consider the genetic diversity of impacted species when predicting the impact and necessary conservation measures of large‐scale land‐cover changes on species with small population sizes.

Species delimitation, biogeography, and natural history of dwarf funnel web spiders (Mygalomorphae, Hexurellidae, Hexurella) from the United States / Mexico borderlands.

The rarely encountered spider genus Hexurella Gertsch & Platnick, 1979 includes some of the smallest mygalomorph spiders in the world, with four poorly known taxa from central and southeastern montane Arizona, southern California, and northern Baja California Norte. At time of description the genus was known from fewer than 20 individuals, with sparse natural history information suggesting a vagrant, web-building, litter-dwelling natural history. Here the first published taxonomic and natural history information for this taxon is provided in more than 50 years, working from extensive new geographic sampling, consideration of male and female morphology, and sequence capture-based nuclear phylogenomics and mitogenomics. Several new species are easily diagnosed based on distinctive male morphologies, while a complex of populations from central and northern Arizona required an integrative combination of genomic algorithmic species delimitation analyses and morphological study. Four new species are described, including H.ephedrasp. nov., H.uwiiltilsp. nov., H.xericasp. nov., and H.zassp. nov. Females of H.encina Gertsch & Platnick, 1979 are also described for the first time. It is predicted that additional new species will ultimately be found in the mountains of central and northwestern Arizona, northern mainland Mexico, and the Mojave Desert of California.

Petrography, mineralogy, and geochemistry of nitrogenous shale in the Western Desert of Egypt: implications for paleoenvironment

Besides nitrate deposits located in the Atacama Desert of Chile and the Mojave Desert of California, the present work documents, for the first time, the occurrence of potassium nitrate as oval-suboval-shaped aggregations associated with the Late Maastrichtian-Early Paleocene Dakhla Shale and the Paleocene-Early Eocene Esna Shale encountered in the northeastern part of the Kharga Oasis, particularly at G. Um El-Ghanayem and G. Ghaneima. Consequently, integrated petrographic, mineralogical, and geochemical investigations were carried out for shale deposits and nitrate salts to reconstruct the paleoenvironmental conditions of shale, reveal the extent to which nitrate salts are genetically related to the paleoenvironment of shale deposits, and build up a complete scenario about the source and the formation mechanism of nitrate salts. The overall results showed that the studied shale deposits were sourced from mafic igneous and quartzose sedimentary provenances where humid climatic conditions were dominant; the transported detrital particles were then settled down under oxidizing bottom water and shallow depositional conditions. Moreover, the nitrate salts are of an epigenetic origin and sourced from the microbial nitrification of organic matter and the wet atmospheric deposition that is believed to be triggered by the active volcanic eruptions during the Late Eocene/Early Oligocene transition where warm climatic conditions prevailed.

Drivers of survival of translocated tortoises

AbstractTranslocation of animals, especially for threatened and endangered species, is a currently popular but very challenging activity. We translocated 158 adult Agassiz's desert tortoises (Gopherus agassizii), a threatened species, from the National Training Center, Fort Irwin, in the central Mojave Desert in California, USA, to 4 plots as part of a long‐distance, hard‐release, mitigation‐driven translocation to prevent deaths from planned military maneuvers. We monitored demographic and behavioral variables of tortoises fitted with radio‐transmitters from 2008 to 2018. By the end of the project, 17.72% of tortoises were alive, 65.82% were dead, 15.19% were missing, and 1.27% were removed from the study because they returned to Fort Irwin. Mortality was high during the first 3 years: >50% of the released animals died, primarily from predation. Thereafter, mortality declined but remained high. After 10.5 years, survival was highest, 37.50% (15/40), on the plot closest to original home sites, whereas from 2.56% to 23.68% remained alive on the other 3 release plots. Surviving tortoises settled early, repeatedly using locations where they constructed burrows, compared with tortoises that died or disappeared. Models of behavioral and other variables indicated that numbers of repeatedly used locations (burrows) were a driver of survival throughout the study, although plot location, size and sex of tortoises, and distance traveled were contributors, especially during early years. Because >50% mortality occurred, we considered this translocation unsuccessful. The study area appeared to be an ecological sink with historical and current anthropogenic uses contributing to habitat degradation and a decline in both the resident and released tortoises. Our findings will benefit design and selection of future translocation areas.

Local differences in maximum temperature determine water use among desert bighorn sheep populations

AbstractThe availability of surface water is assumed by many wildlife managers to be important to desert bighorn sheep (Ovis canadensis nelsoni). Yet scientific evidence suggests bighorn sheep populations can sometimes fulfill their water requirements from forage alone. To investigate how water use changes with environmental conditions, we analyzed the surface water use and movement patterns of 4 desert bighorn populations across a range of meteorological conditions in the Mojave Desert in California, USA. We compared ground‐based weather data to the daily use of surface water sources for 65 known individuals, and examined the movement patterns of 18 of these individuals with global positioning system collars in relation to visitation to surface water sources. Maximum daily temperature most closely predicted the percent of bighorn visiting water daily, with visitation increasing approximately 30% between 30°C and 40°C. Individual animals switched from a tortuous foraging movement to directed movement when accessing surface water. Day length, maximum daily temperature, minimum daily temperature, solar radiation, and the interaction between day length and minimum temperature explained the distance desert bighorn were located from the nearest water source. Our results indicate that local meteorological conditions are important determinants of desert bighorn surface water use, and that managers should monitor water sources when the maximum daily temperature exceeds 35°C. Individual animals meet their water requirements with surface water under hot and dry conditions, likely because it is temporally or energetically efficient given their other resource needs.

Aleurocybotus mojavensis (Hemiptera: Sternorrhyncha: Aleyrodidae), a new whitefly species from California.

A new species of Aleurocybotus Quaintance Baker, 1914 found on grasses in the Mojave Desert in California, U.S.A., is described, figured, and diagnosed from its congeners. It can be easily recognized from A. occiduus Russell, 1964, the only other species of this genus present in California, by the copious white woolly wax secretions of its puparia and corresponding dorsal submarginal glandular band, and from A. cereus Martin, 2005, the only other Aleurocybotus species that produces large amounts of white wax, by its narrower glandular band, shape of vasiform orifice and operculum, and several other cuticular characters. A key to identify puparia of all described species of Aleurocybotus is provided.

Allometry of unifacial flake tools from Mojave Desert terminal pleistocene/early holocene sites: Implications for landscape knowledge, tool design, and land use

This study evaluates the allometry of terminal Pleistocene-early Holocene age unifacial flake tools in the northcentral Mojave Desert of California to reveal linkages between landscape knowledge, tool design, and land use. Analyses of 438 unifacial flake tools (all types) show at the population scale that Mojave Desert Paleoindians, like other post-Clovis Paleoindians across North America, possessed good knowledge of the landscape and designed flake tools for short-term purposes. This design strategy repeats in three study areas but to varying degrees: flake tools in the Fort Irwin study area were designed for shorter-term use than those from the pluvial China Lake and Lake Mojave study areas. Chert flake tools were designed for somewhat shorter-term use than those made from fine-grained volcanic stones, with obsidian flake tools designed for longevity. The regional ubiquity of knappable lithic raw materials, especially cherts, partially explains the short-term design strategy given Paleoindians’ knowledge of the landscape, including where to find knappable stones. Given that the design strategy of unifacial flake tools varies by raw material type, it provides a reminder that Great Basin Paleoindian land use models derived solely or largely from obsidian projectile points and bifacial tools may result in biased interpretations.

Current status of the Mohave ground squirrel: an update covering the period 2013–2020

The Mohave ground squirrel (Xerospermophilus mohavensis) is endemic to the western Mojave Desert of California. It is restricted to a small geographic area and is listed as Threatened under the California Endangered Species Act. Human development has resulted in loss and degradation of its desert habitat and climate change is believed to pose an additional threat. To determine its current conservation status and geographic distribution, I have assembled all available data from field studies during the years 2013-2020. These data confirm that the species is still present in 4 core areas and that it continues to be widespread in the northern and central portions of its historical range. However, the recent data also confirm earlier conclusions that the Mohave ground squirrel is now extirpated from the southernmost portion of its range. Recent surveys raise concerns about its status in other areas as well. A large-scale trail camera survey on the South Range unit of China Lake Naval Air Weapons Station in 2019 failed to detect the Mohave ground squirrel over much of this large installation. Recent trail camera surveys on Fort Irwin strongly suggest that the closely-related round-tailed ground squirrel (Xerospermophilus tereticaudus) has now replaced the Mohave ground squirrel over most of the base. There is additional evidence that the round-tailed ground squirrel is present in disturbed habitats to the west of Barstow and that hybridization with the Mohave ground squirrel is occurring there. It will be important to protect and conserve currently occupied Mohave ground squirrel habitat in view of this new information.

Previously Unrecognized Exposure of Desert Bighorn Sheep (Ovis canadensis nelsoni) to Mycoplasma ovipneumoniae in the California Mojave Desert

A 2013 outbreak of respiratory disease in bighorn sheep from California's Mojave Desert metapopulation caused high mortality in at least one population. Subsequent PCR and strain-typing indicate widespread infection of a single strain of Mycoplasma ovipneumoniae throughout this region. Serosurvey of archived samples showed that some populations have had antibodies to M. ovipneumoniae since at least 1986, although pre-2013 strain-type data are unavailable.

Predation on desert tortoises (Gopherus agassizii) by desert canids

Desert tortoises (Gopherus agassizii) are a long-lived reptile vulnerable to predation by many predators, including desert kit foxes (Vulpes macrotis arsipus) and coyotes (Canis latrans). From 2009 to 2014, we assessed canid food habits at a study site in the Mojave Desert in California, USA, by collecting and analyzing desert kit fox and coyote scats. These canids primarily consumed small mammals and invertebrates. Desert tortoise remains occurred at an overall low frequency (<3%), indicating the opportunistic use by these canids of desert tortoise as a prey or scavenged food item. When we analyzed the desert tortoise remains further, there was a significant difference between predator type and desert tortoise age class. Coyotes consumed more than twice as many adult than juvenile desert tortoises, while desert kit foxes only consumed juveniles. Desert kit foxes are a small canid, thus limited to smaller prey items (i.e., juvenile desert tortoises), while coyotes are larger and can optimize a wider size range.

Vascular Plants of Northern Death Valley National Park (Death Valley, Last Chance Range, and Eureka Valley), Inyo County, California

The northern portion of Death Valley National Park closely (but not entirely) corresponds to the northernmost portion of the Mojave Desert in California. From 2014 through 2019 we surveyed the vascular plants in the Eureka Valley, northern Last Chance Range, and northern Death Valley. This study area covers 1735 sq km and ranges in elevation from 810 to 2577 m; it contains the tallest sand dunes in California, a calcium-rich mountain range, and alkaline seeps. These features provide specialized habitats for narrowly and regionally endemic plants. Fossil data from packrat middens suggest that the local climate has become warmer and drier during the Holocene and the assemblage of plants currently observed has only been in place for a few thousand years. During six years of fieldwork, we documented 542 specimens of minimum-rank taxa, including 51 special concern taxa and 25 non-natives. We were unable to relocate 45 taxa known from historic collections. Fifty-one collections were the first for the study area; these include 24 range extensions. Observations from our collections are combined with those from historic collections and other collectors in an annotated checklist.

Survival of Adult Female Bighorn Sheep Following a Pneumonia Epizootic

ABSTRACTBeginning in the early 1900s, poly‐factorial, poly‐microbial pneumonia was identified as a disease affecting bighorn sheep (Ovis canadensis) and it continues to threaten bighorn populations, posing an ongoing management challenge. In May and June 2013, a pneumonia outbreak linked to the pathogen Mycoplasma ovipneumoniae led to an all‐age die‐off of desert bighorn sheep (O. c. nelsoni) at Old Dad Peak in the Kelso Mountains of the Mojave Desert in California, USA. Subsequently, we observed clinical signs of respiratory disease among bighorn sheep in multiple neighboring ranges. Our objective was to investigate post‐outbreak survival of adult female bighorn across 9 populations from 2014 to 2017 in the Mojave Desert and evaluate the relationship between M. ovipneumoniae infection and survival, while testing effects of range factors that could potentially influence differences in adult female survival (i.e., forage quality, winter precipitation, population abundance). We fitted adult females with radio‐collars following the outbreak and collected serum and nasal swab samples for competitive enzyme‐linked immunosorbent assay (cELISA) and polymerase chain reaction (PCR) testing to determine exposure and infection status at time of capture. We tracked survival of 115 adult females with radio‐collars and used the known‐fate model in Program MARK to evaluate effects and estimate survival from November 2013 to March 2017. Annual survival was negatively correlated with positive infection status at capture but varied across populations with respect to differences in range conditions. Summer and autumn forage quality, as represented by mean normalized difference vegetation index (NDVI) values for summer and autumn, was positively correlated with overwinter survival, whereas winter precipitation (a proxy for winter severity) was negatively correlated with overwinter survival. Population abundance was negatively correlated with annual survival, suggesting a potential density‐dependent effect. Model‐averaged annual survival estimates ranged from 0.700 ± 0.07 (SE) to 0.945 ± 0.026 for infected individuals and 0.896 ± 0.03 to 0.983 ± 0.011 for uninfected individuals. We conclude that summer and autumn forage quality, indexed by NDVI, may partially offset the negative effect associated with M. ovipneumoniae infection on host survival. Our survival modeling results suggest that chronic infection may have afflicted adult females that were PCR‐positive (i.e., infected with M. ovipneumoniae) at time of capture. We propose programmatic re‐testing of infected individuals to assess pathogen persistence at the individual level and evaluate whether selective culling might potentially help to reduce prevalence and transmission within populations. © 2020 The Wildlife Society.

Earthquake-Ridden Area in USA Contains Coccidioides, the Valley Fever Pathogen.

Early July 2019, two major earthquakes occurred in the Mojave Desert of California near the city of Ridgecrest and the community of Trona and generated a large dust plume that lingered for days. The earthquakes hit an area endemic for Coccidioides, a soil-borne fungal pathogen that can become airborne when soil is disturbed and typically manifests as a pulmonary disease when inhaled. This study is the first to confirm the presence of Coccidioides in soils near Trona using a nested polymerase chain reaction (PCR) approach. First responders to earthquake events, the public, and physicians in the San Joaquin Valley and the Mojave Desert should be informed about the risk of pathogen exposure during and after the time of an earthquake, since there are many fault lines in addition to the large San Andreas Fault and future earthquakes in this region are expected to occur.

Simulated solar panels create altered microhabitats in desert landforms

AbstractSolar energy development is a significant driver of land‐use change worldwide, and desert ecosystems are particularly well suited to energy production because of their high insolation rates. Deserts are also characterized by uncertain rainfall, high species endemism, and distinct landforms that vary in geophysical properties. Weather and physical features that differ across landforms interact with shade and water runoff regimes imposed by solar panels, creating novel microhabitats that influence biotic communities. Endemic species may be particularly affected because they often have limited distributions, narrow climatic envelopes, or specialized life histories. We used experimental panels to simulate the effects of solar development on microhabitats and annual plant communities present on gravelly bajada and caliche pan habitat, two common habitat types in California's Mojave Desert. We evaluated soils and microclimatic conditions and measured community response under panels and in the open for seven years (2012–2018). We found that differences in site characteristics and weather affected the ecological impact of panels on the annual plant community. Panel shade tended to increase species richness on the more stressful caliche pan habitat, and this effect was strongest in dry years. Shade effects on diversity and abundance also tended to be positive or neutral on caliche pan habitat. On gravelly bajada habitat, panel shade did not significantly affect richness or diversity and tended to decrease plant abundance. Panel runoff rarely affected richness or diversity on either habitat type, but effects on abundance tended to be negative—suggesting that panel rain shadows were more important than runoff from low‐volume rain events. These results demonstrate that the ecological consequences of solar development can vary over space and time, and suggest that a nuanced approach will be needed to predict impacts across desert landforms differing in physical characteristics.

Large-eddy simulation of flash flood propagation and sediment transport in a dry-bed desert stream

A Large-Eddy Simulation (LES) model is used to study flow dynamics of a flash flood event in a dry-bed, desert wash, the so-called Tex Wash, near the Tex Wash Bridge on Interstate 10 in the Mojave Desert of California. The evolving free surface of the flash flood is tracked using the level-set method. A bed morphodynamics module is coupled to the hydrodynamics model to calculate the erosion and bed evolution of the mobile bed of the wash under flash flood conditions. Flash floods in a desert wash can be characterized with a number of salient features such as the (1) existence of both the dry- and wet-cells on the bed surface of the wash that correspond to the air and water phases, respectively; (2) presence of various flow regimes, critical, sub-critical, and super-critical in the flow domain; and (3) occurrence of a highly transient and complicated flow field and, subsequently, sediment dynamics throughout the wash. A numerical modeling effort is presented to study a recorded flash flood and the corresponding scour processes in the Tex Wash. The flood event occurred in 2015 and lead to the collapse of the Tex Wash Bridge. The of the current study is to gain insight into the flood flow and sediment transport mechanisms, which resulted in the collapse of the bridge. To that end, a study area, which includes a 0.65 km-long reach of Tex Wash at its intersection with the Tex-Wash Bridge, was selected. The bathymetry of the wash was obtained using light-detection-and-ranging (LiDAR) technology and used to construct the computational domain of the wash and bridge foundations. The transient flow of the flash flood, in both air and water phases, and the evolving morphology of the wash are numerically simulated. The site-specific numerical simulation revealed the formation of deep scour regions adjacent to the right abutment of the upstream bridge, where significant erosion caused the collapse of the bridge. Moreover, the results show that most of the scour processes take place during the steady phase of the flash flood when the desert stream is filled with water. However, the transient phase of the flash flood is rather short and contributes to a very limited amount of erosion within the stream.

An Uncertain Future for a Population of Desert Tortoises Experiencing Human Impacts

Abstract We evaluated the status of a population of Mojave Desert Tortoises (Gopherus agassizii), a threatened species, in the El Paso Mountains of the northwestern Mojave Desert in California, USA...

Exploitative competition between desert kit foxes and coyotes in the Mojave Desert

Exploitative competition between two sympatric guild members can influence the composition and dynamics of an ecological community. We assessed potential exploitative competition between desert kit foxes (Vulpes macrotis arsipus) and coyotes (Canis latrans) by comparing food habits of the two species from 2009 to 2014 on a study site in the Mojave Desert in California. Desert kit foxes specialised on heteromyid rodents and invertebrates, while the most frequently occurring items consumed by coyotes were lagomorphs and rodents. Both species consumed a variety of food items throughout the study, but relative use of these items varied with year and season. Also, precipitation affected prey abundance, and this influenced prey consumption by the two species. The diets of desert kit foxes and coyotes overlapped extensively, which indicated possible exploitative competition. Desert kit foxes consistently had lower dietary diversity than coyotes, indicating that desert kit foxes are more specialist consumers while coyotes are more generalists. Dietary specialisation by kit foxes on smaller items may help reduce competition with coyotes and facilitate coexistence. Coyotes consumed anthropogenic material at much higher frequencies than desert kit foxes, and this subsidisation could increase competitive pressures on kit foxes if it results in greater coyote abundance. Desert kit foxes in California are not a protected species although formal protection has been proposed due to increasing human encroachment. Conservation strategies should include measures to maintain an abundance and diversity of natural food items and limit anthropogenic subsidisation of coyotes.

Reflect on this

Heliostat mirrors are sunflower-like reflectors that turn to track the sun during the day. These are just two of hundreds of thousands such mirrors arranged in the Mojave Desert in California, all part of the Ivanpah solar power project. Their job is to concentrate the sun's rays onto boilers located on three central towers, turning water into steam that drives turbines. The site covers 14 square kilometers and will produce at least 377 megawatts of electricity not much below the summer output of a typical nuclear power station in the US and enough to power 140,000 homes in California

Hierarchical distance sampling to estimate population sizes of common lizards across a desert ecoregion.

Multispecies wildlife monitoring across large geographical regions is important for effective conservation planning in response to expected impacts from climate change and land use. Unlike many species of birds, mammals, and amphibians which can be efficiently sampled using automated sensors including cameras and sound recorders, reptiles are often much more challenging to detect, in part because of their typically cryptic behavior and generally small body sizes. Although many lizard species are more active during the day which makes them easier to detect using visual encounter surveys, they may be unavailable for sampling during certain periods of the day or year due to their sensitivity to temperature. In recognition of these sampling challenges, we demonstrate application of a recent innovation in distance sampling that adjusts for temporary emigration between repeat survey visits. We used transect surveys to survey lizards at 229 sites throughout the Mojave Desert in California, USA, 2016. We estimated a total population size of 82 million (90% CI: 65–99 million) for the three most common species of lizards across this 66,830 km2 ecoregion. We mapped how density at the 1‐km2 scale was predicted to vary with vegetation cover and human development. We validated these results against independent surveys from the southern portion of our study area. Our methods and results demonstrate how multispecies monitoring programs spanning arid ecoregions can better incorporate information about reptiles.

Exergy analysis of a hybrid solar‐fossil fuel power plant

AbstractIn this study, exergy analysis, energy analysis, and mathematical modeling are performed in a 35 MW solar‐fossil fuel power plant. The losses of exergy and energy in different components and also changes of the efficiency of exergy and energy are analyzed at a specific day, 20th June. The assumed power plant in this study is Solar Electric Generating Station VI (SEGS VI), located in California's Mojave Desert. A parametric study, under different working conditions, including different working pressures, temperatures, collector output temperature, steam flow rate, and heat transfer fluid (HTF) flow rate is studied and the effect of variation of parameters on the performance of the plant is investigated. Authors found that, the maximum exergy loss happens in the collector and the maximum energy loss occurs in the condenser. Energy analysis shows that 47% of the total loss energy in the cycle happens in the condenser, as the main component that wastes energy. From exergy analysis, the collector and then boiler are the main components wasting exergy where 68.32% of total exergy loss occurs in these two components in hybrid mode (solar‐fossil fuel). Exergy and Energy efficiency variations throughout the day show that minimum exergy efficiency (32.7%) and maximum energy efficiency (23%) occurs at 12 am. Exergy efficiency variation versus turbine inlet pressure shows that the maximum exergy efficiency (26%) accure at 95 bar. The changes of the absorbed heat and solar irradiation of the 20th of June shows a good agreement with the measured data in validated reference.