Search

Carnivores play critical roles in ecosystems, yet many species are declining worldwide. The Sierra Nevada Red Fox (Vulpes vulpes necator; SNRF) is a rare and endangered subspecies of red fox limited to upper montane forests, subalpine, and alpine environments of California and Oregon, United States. Having experienced significant distribution contractions and population declines in the last century, the subspecies is listed as at-risk by relevant federal and state agencies. Updated information on its contemporary distribution and density is needed to guide and evaluate conservation and management actions. We combined 12 years (2009-2020) of detection and nondetection data collected throughout California and Oregon to model the potential distribution and density of SNRFs throughout their historical and contemporary ranges. We used an integrated species distribution and density modeling approach, which predicted SNRF density in sampled locations based on observed relationships between environmental covariates and detection frequencies, and then projected those predictions to unsampled locations based on the estimated correlations with environmental covariates. This approach provided predictions that serve as density estimates in sampled regions and projections in unsampled areas. Our model predicted a density of 1.06 (95% credible interval = 0.8-1.36) foxes per 100 km2 distributed throughout 22,926 km2 in three distinct regions of California and Oregon-Sierra Nevada, Lassen Peak, and Oregon Cascades. SNRFs were most likely to be found in areas with low minimum temperatures and high snow water equivalent. Our results provide a contemporary baseline to inform the development and evaluation of conservation and management actions, and guide future survey efforts.

As anthropogenic disturbances continue to drive habitat loss and range contractions, the maintenance of evolutionary processes will increasingly require targeting measures to the population level, even for common and widespread species. Doing so requires detailed knowledge of population genetic structure, both to identify populations of conservation need and value, as well as to evaluate suitability of potential donor populations. We conducted a range-wide analysis of the genetic structure of red foxes in the contiguous western U.S., including a federally endangered distinct population segment of the Sierra Nevada subspecies, with the objectives of contextualizing field observations of relative scarcity in the Pacific mountains and increasing abundance in the cold desert basins of the Intermountain West. Using 31 autosomal microsatellites, along with mitochondrial and Y-chromosome markers, we found that populations of the Pacific mountains were isolated from one another and genetically depauperate (e.g., estimated Ne range = 3-9). In contrast, red foxes in the Intermountain regions showed relatively high connectivity and genetic diversity. Although most Intermountain red foxes carried indigenous western matrilines (78%) and patrilines (85%), the presence of nonindigenous haplotypes at lower elevations indicated admixture with fur-farm foxes and possibly expanding midcontinent populations as well. Our findings suggest that some Pacific mountain populations could likely benefit from increased connectivity (i.e., genetic rescue) but that nonnative admixture makes expanding populations in the Intermountain basins a non-ideal source. However, our results also suggest contact between Pacific mountain and Intermountain basin populations is likely to increase regardless, warranting consideration of risks and benefits of proactive measures to mitigate against unwanted effects of Intermountain gene flow.

Declines in populations of small mammals associated with high elevations, e.g. marmots (Marmota spp.) and pikas (Ochotona spp.), have been attributed to both direct and indirect effects of environmental changes caused by humans. For example, populations of Olympic marmots (M. olympus) and Vancouver Island marmots (M. vancouverensis) have declined in response to increased predator access to high-elevation marmot habitats. In the North Cascades National Park Service Complex (NOCA), observed mean abundance of hoary marmots (M. caligata) declined by 74% from 2007 to 2016. Although these declines have been linked to harsh winter conditions, the role of predation and its association with decreasing snowpack has yet to be explored in this system. We noninvasively examined these predator–prey dynamics by coupling behavioral surveys of hoary marmots with indices of predation risk. We conducted 145 vigilance samples and 39 flight initiation distance trials to measure Hoary Marmot antipredator behavior. We derived a risk index for each predator by weighting its probability of use estimates (the probability of a predator–prey encounter) with its observed proportion of Hoary Marmot predation (probability of prey death given an encounter). We used genetic metabarcoding of vertebrate DNA from 413 predator scat samples to quantify predation on hoary marmots. We surveyed 9,930 trap-nights using 130 remote cameras to model predator probability of use near Hoary Marmot colonies. From camera traps and scat DNA, we detected 10 predator species in the study area, and we detected hoary marmots in the scats of 5 of these species. The proportion of observed Hoary Marmot predation was highest for coyotes (Canis latrans) at 50%. To our knowledge, we also report the first record of hoary marmots being consumed by Pacific martens (Martes caurina), which were also significant predators (proportion of observed predation = 32%). We expected predators with low-elevation habits to use sites with lesser snow persistence; this prediction was supported for coyotes but not for other typically low-elevation predators. We found estimated risk experienced by hoary marmots was highest from Pacific martens and lowest from Canada Lynx (Lynx canadensis). Contrary to our predictions and despite hoary marmots allocating >50% of their time to vigilance, neither estimates of predator risk nor human presence explained variation in marmot antipredator behavior. Based on the results from both our dietary and probability of use analyses, we expect coyotes to have an increasing effect on NOCA's Hoary Marmot population as the climate warms and Coyote range continues to expand. Thus, our work highlights the need to better understand the effect of climate-driven shifts in predator–prey ecology in high-elevation systems. [ABSTRACT FROM AUTHOR]

The social system of animals involves a complex interplay between physiology, natural history, and the environment. Long relied upon discrete categorizations of "social" and "solitary" inhibit our capacity to understand species and their interactions with the world around them. Here, we use a globally distributed camera trapping dataset to test the drivers of aggregating into groups in a species complex (martens and relatives, family Mustelidae, Order Carnivora) assumed to be obligately solitary. We use a simple quantification, the probability of being detected in a group, that was applied across our globally derived camera trap dataset. Using a series of binomial generalized mixed-effects models applied to a dataset of 16,483 independent detections across 17 countries on four continents we test explicit hypotheses about potential drivers of group formation. We observe a wide range of probabilities of being detected in groups within the solitary model system, with the probability of aggregating in groups varying by more than an order of magnitude. We demonstrate that a species' context-dependent proclivity toward aggregating in groups is underpinned by a range of resource-related factors, primarily the distribution of resources, with increasing patchiness of resources facilitating group formation, as well as interactions between environmental conditions (resource constancy/winter severity) and physiology (energy storage capabilities). The wide variation in propensities to aggregate with conspecifics observed here highlights how continued failure to recognize complexities in the social behaviors of apparently solitary species limits our understanding not only of the individual species but also the causes and consequences of group formation. [ABSTRACT FROM AUTHOR]

The Sierra Nevada red fox Vulpes vulpes necator is a native subspecies associated with subalpine regions in the Sierra Nevada and Cascade mountain ranges of California and Oregon. In the past century, the Sierra Nevada red fox experienced a major range contraction and decline in California. However, the number, size, and connectivity of populations extant in Oregon remain unclear. This knowledge gap impedes efficient monitoring and hinders development of a cohesive conservation strategy for the subspecies. The historical range is large and includes rugged terrain with low accessibility; therefore, a predictive model is needed to facilitate more comprehensive and systematic surveys in the future. We initiated a multiagency collaborative effort to survey portions of the range in the Oregon Cascades during 2011–2016 (verified genetic and photographic detections) and to assemble existing sighting reports dating back to 1985 (unverified), which we used to create Maxent models to predict the potential distribution of Sierra Nevada red fox within Oregon. To identify optimal levels of model complexity, we compared cross-validation accuracy of models that varied in levels of protection against overfitting (regularization). The highest-performing models utilized intermediate regularization, and included minimum January temperature and land-cover type. Regardless of regularization or data set (verified detections, all putative detections), all models agreed in predictions of a high-probability region covering approximately 3,470 km2 or 6% of the Cascade region, corresponding to the high-elevation portion of the crest. With the exception of a gap between Mount Hood and Mt. Jefferson, this core area of predicted presence was continuous along the north–south extent of the crest, suggesting a capacity for high connectivity among observed clusters of occurrence. Use of modeled potential distributions in future survey design will improve efficiency of field data collection, facilitating more precise evaluations of the distribution, abundance, and genetic integrity and connectivity of Sierra Nevada red fox in Oregon. [ABSTRACT FROM AUTHOR]

The Cascade red fox (CRF) occurred historically throughout subalpine and alpine habitats in the Cascade Range of Washington and southernmost British Columbia, but now appears to be extremely rare. Causes for its apparent decline are unknown, as is the current distribution and connectivity of its populations. Additionally, the introduction of nonnative (fur-farm) red foxes to surrounding lowland areas during the past century raises concerns about their expansion to higher elevations and potential hybridization with the CRF. We conducted noninvasive genetic sampling and analyses of CRFs in a 5575 km2 region in the southern portion of its range, which is thought to contain a significant proportion of the current population. We obtained 154 mitochondrial DNA sequences and microsatellite genotypes for 51 individuals to determine trends in genetic diversity, assess evidence for nonnative introgression, and describe population structure. Although heterozygosity (He = 0.60, SE = 0.03) was only slightly lower than an estimate obtained from samples collected during the 1980s (He = 0.64, SE = 0.05), genetic effective size of the current population based on a one-sample estimate was very small (Ne = 16.0, 95% CI 13.3-19.4), suggesting a loss of genetic diversity and the potential for inbreeding depression in future decades. Genetic connectivity was high and we found no evidence for hybridization with nonnative lowland red foxes. Thus, although a small effective population size indicates the possibility of inbreeding depression and loss of evolutionary potential, high connectivity and genetic integrity could mitigate this to some extent, indicating that the population could respond to conservation efforts. Ultimately, successful conservation of this species depends on a better understanding of the factors that originally contributed to its decline and that currently limit its growth. [ABSTRACT FROM AUTHOR]