Geology Reports⌕ Search

Geology topics

David Stoner

Publications and source records attributed to David Stoner.

7 recordsLinked to original sources
USGS2026

Mountain lion prey-selection in a community comprised of native and introduced ungulate species

Species introductions are a hallmark of human influence on ecosystems worldwide. In communities where native and introduced fauna coexist, predators may select prey based on availability or vulnerability. Free-roaming feral horses ( Equus caballus ) are a recent addition to North America and have become widespread, abundant, and in some areas serve as major prey for mountain lions ( Puma concolor ), a native carnivore. The proliferation of horses as well as potential effects of mountain lion predation on native ungulates create ecological and social management challenges; our goal was to assess mountain lion prey selection in a system composed of native mule deer ( Odocoileus hemionus ) and introduced feral horses. Our objectives were to: (1) describe seasonal patterns of prey use within individual mountain lion home ranges; (2) quantify prey use relative to availability; and (3) determine seasonal kill rates on the two primary ungulates in the study area. Fieldwork occurred in southeastern Nevada, 2021–2022. We identified prey use by investigating cache sites from 6 GPS-collared mountain lions. Prey availability and relative abundance were estimated with 49 camera traps distributed across the 3,158-km² study area. During the growing season, weekly kill rates averaged 0.22 deer and 0.55 horses, and in winter, 1.43 deer and 0.33 horses. Thus, lions killed horses at 2.54 times the rate of deer in the growing season but deer at 4.33 times the rate of horses in winter. Model selection indicated mule deer density and prey age class were the strongest predictors of prey species. Lions selected adult deer over fawns, and foals over adult horses, suggesting choices may be driven by optimal prey size rather than species. Mountain lions prey on foals in areas with relatively high mule deer densities, suggesting deer presence may increase foal vulnerability. We hypothesize that lions select foals when available, potentially reducing pressure on mule deer and/or supporting larger lion populations than would occur without this additional prey source. Although individual-level data on mountain lions are challenging to obtain, such information could help managers identify individuals for removal or conservation, improving predator-management outcomes in mixed-prey systems.

Nevada↗
USGS2026

Effects of mountain lion predation on reducing feral horse population growth rates: Panacea or pipedream?

A goal of applied ecology is to evaluate how demographic rates contribute to population growth and how demography might be manipulated to achieve management objectives. In western North America, many feral horse ( Equus caballus ) populations occupying public lands are protected by federal law and managed for site-specific numerical targets. However, feral horses can exhibit population growth rates exceeding 20% per yr, which can lead to overpopulation, and therefore conflict with other permitted land uses. In response, some stakeholder groups have advocated for natural solutions to the problem of rapid growth and overabundance. Mountain lion ( Puma concolor ) predation has been hypothesized to have suppressive effects on horse population growth rates under some conditions. Here, we evaluated the degree to which this phenomenon might reduce feral horse growth rates using elasticity analysis, scenario analysis with simulations, and an empirical state-space model for a horse population in southeastern Nevada subject to chronic predation. Age-specific elasticities revealed that annual population growth rates (λ) were more sensitive to perturbations in foal and yearling survival rates than for older age-classes. This finding, in conjunction with empirical measures indicating that foals comprised approximately 60% of horses killed by mountain lions, suggests that predation may have greater potential to reduce horse population growth rates than previously recognized. Scenario analysis predicted that horse populations could decrease to target levels within 10 years if predation reduced: (1) annual foal survival by 80% each year, or (2) annual survival rates of foals, yearlings, and 2-year olds by >60%. The state-space model indicated that the heavily predated Nevada horse population experienced positive population growth during 2022 and 2023 (λ = 1.07, both years). Using information on known predation-caused mortalities from 2020–2021, our model predicted that population growth rate in the absence of predation (‘predicted λ’) would have been approximately twice as high (predicted λ 2020 = 1.14; predicted λ 2021 = 1.14 in 2021). Taken together, our results suggest that predation is unlikely to singularly induce stable or negative population growth of feral horses. That said, our findings suggest two aspects of predation that may benefit resource managers. First, chronic predation may reduce λ, thereby increasing the time required for populations to either recover from declines, or exceed management objectives; and second, predation may be most effective in achieving management objectives for horse populations when combined with other interventions, such as removals or fertility control treatments.

Nevada↗
USGS2026

Quantifying free-roaming horse body condition: A methodological investigation using game cameras and observer bias corrections

Large populations of free-roaming horses (Equus caballus ) inhabit the western United States, Australia, and other arid and semi-arid rangelands globally. In the United States, horse body condition has been the impetus for gathering and removing horses under an emergency designation and has been noted as a common chronic mortality-causing condition. The Henneke body condition scoring (BCS) system is a qualitative index that includes visual appraisal and physical palpation at multiple anatomical locations on individual horses. This method has been shown to be repeatable between different observers with varying degrees of experience when assessing domestic horses at close proximity. Repeatability using the Henneke BCS system is unknown for free-roaming equids in vast environments, and adequately sampling populations in a minimally biased manner can be logistically challenging. However, estimating body condition using photographs has been shown to be a highly accurate alternative to proximal scoring for multiple scoring systems and species. Our study investigates if an automated, remote camera trap system can be used to estimate free-roaming equid body condition. We compiled existing camera trap data sets from 65 traps into a single data set including more than 3.7 million photos containing images of free-roaming horses from California, Nevada, Utah, and Wyoming. We employed veterinarian-trained animal science students to score horses within randomly sampled, spatially/temporally congruous sequences of animals in our data sets. We compared student scores with veterinarian scores to evaluate whether scorer-specific correction factors are necessary for estimating BCS parameters. Calibration to a fixed reference set reduced between-scorer variance to zero in our population-level BCS estimates. Analysis of our between-scorer variance in our empirical data implies this calibration step can be beneficial when different observers are scoring distinct horse populations across space and/or time.

California, Nevada, Utah, Wyoming↗
USGS2025

Dynamic riskscapes for prey: Disentangling the impact of human and cougar presence on deer behavior using GPS smartphone locations

Prey species adjust their behavior along human-use gradients by balancing risks from predators and humans. During hunting seasons, prey often exhibit strong antipredator responses to humans but may develop tolerance in suburban areas to exploit human-mediated resources. Additionally, areas with high human activity may offer reduced predation risk if apex predators avoid such locations. This study examined mule deer Odocoileus hemionus behavioral responses to risks from humans and their primary predators, cougars Puma concolor , contextualized by differences in risk levels between study sites, individual risk exposure, and human habituation. We framed our investigation using three non-mutually exclusive hypotheses: (H1) neutral impact, (H2) human shielding (human tolerance driven by cougar avoidance), and (H3) super-additive risk (human avoidance dominating behavior). We controlled for deer phenology and diel period, recognizing that deer behavior varies with these temporal dynamics. Spatiotemporal cougar encounter risk was quantified using GPS collar data, while spatiotemporal human encounter risk and use intensity were quantified using GPS smartphone data. Our results supported H2 and H3, emphasizing the significance of site- and individual-level variation in risk exposure and human use intensity. Deer managed cougar risk adaptively, but humans emerged as the dominant perceived risk, varying by study site. At the site with higher cougar density and lower human hunting pressure, deer exhibited antipredator responses to humans based on individual exposure to human activity, except during hunting season, when tolerance for cougars increased. Conversely, humans were the dominant risk at the site with lower cougar density and greater human hunting pressure. Deer behavior varied significantly across a gradient of human use, influenced by nuanced human presence and predation risks, which were discernible using human smartphone data.

Colorado, Utah↗
USGS2017

Variable terrestrial GPS telemetry detection rates: Addressing the probability of successful acquisitions

Studies using global positioning system (GPS) telemetry rarely result in 100% fix success rates (FSR), which may bias datasets because data loss is systematic rather than a random process. Previous spatially explicit models developed to correct for sampling bias have been limited to small study areas, a small range of data loss, or were study-area specific. We modeled environmental effects on FSR from desert to alpine biomes, investigated the full range of potential data loss (0–100% FSR), and evaluated whether animal body position can contribute to lower FSR because of changes in antenna orientation based on GPS detection rates for 4 focal species: cougars ( Puma concolor ), desert bighorn sheep ( Ovis canadensis nelsoni ), Rocky Mountain elk ( Cervus elaphus nelsoni ), and mule deer ( Odocoileus hemionus ). Terrain exposure and height of over story vegetation were the most influential factors affecting FSR. Model evaluation showed a strong correlation (0.88) between observed and predicted FSR and no significant differences between predicted and observed FSRs using 2 independent validation datasets. We found that cougars and canyon-dwelling bighorn sheep may select for environmental features that influence their detectability by GPS technology, mule deer may select against these features, and elk appear to be nonselective. We observed temporal patterns in missed fixes only for cougars. We provide a model for cougars, predicting fix success by time of day that is likely due to circadian changes in collar orientation and selection of daybed sites. We also provide a model predicting the probability of GPS fix acquisitions given environmental conditions, which had a strong relationship ( r 2 = 0.82) with deployed collar FSRs across species.

Wildlife Society Bulletin↗
USGS2016

Ungulate reproductive parameters track satellite observations of plant phenology across latitude and climatological regimes

The effect of climatically-driven plant phenology on mammalian reproduction is one key to predicting species-specific demographic responses to climate change. Large ungulates face their greatest energetic demands from the later stages of pregnancy through weaning, and so in seasonal environments parturition dates should match periods of high primary productivity. Interannual variation in weather influences the quality and timing of forage availability, which can influence neonatal survival. Here, we evaluated macro-scale patterns in reproductive performance of a widely distributed ungulate (mule deer, Odocoileus hemionus ) across contrasting climatological regimes using satellite-derived indices of primary productivity and plant phenology over eight degrees of latitude (890 km) in the American Southwest. The dataset comprised > 180,000 animal observations taken from 54 populations over eight years (2004–2011). Regionally, both the start and peak of growing season (“Start” and “Peak”, respectively) are negatively and significantly correlated with latitude, an unusual pattern stemming from a change in the dominance of spring snowmelt in the north to the influence of the North American Monsoon in the south. Corresponding to the timing and variation in both the Start and Peak, mule deer reproduction was latest, lowest, and most variable at lower latitudes where plant phenology is timed to the onset of monsoonal moisture. Parturition dates closely tracked the growing season across space, lagging behind the Start and preceding the Peak by 27 and 23 days, respectively. Mean juvenile production increased, and variation decreased, with increasing latitude. Temporally, juvenile production was best predicted by primary productivity during summer, which encompassed late pregnancy, parturition, and early lactation. Our findings offer a parsimonious explanation of two key reproductive parameters in ungulate demography, timing of parturition and mean annual production, across latitude and changing climatological regimes. Practically, this demonstrates the potential for broad-scale modeling of couplings between climate, plant phenology, and animal populations using space-borne observations.

Arizona, Colorado, Utah↗