Tule Elk Research Articles

Genetic structure of California's elk: a legacy of extirpations, reintroductions, population expansions, and admixture

AbstractCalifornia, USA, is home to 3 subspecies of North American elk (Cervus canadensis): Roosevelt (C. c. roosevelti), Rocky Mountain (C. c. nelsoni), and tule (C. c. nannodes). Effective management requires a baseline understanding of each subspecies' range, admixture zones, and geographic patterns of genetic diversity. To address these questions, we genotyped 1,271 individual elk from California (n = 1,204) and reference populations of Rocky Mountain and Roosevelt elk from Nevada (n = 32) and Oregon (n = 35), USA. Using 19 polymorphic microsatellite loci, we detected admixture between Roosevelt and Rocky Mountain elk at a contact zone in northern California, and between Roosevelt and tule elk in north‐coastal California and central‐coastal California. We identified a genetically distinct population of Roosevelt elk in northwestern California, likely reflecting the remnant population that survived a large demographic decline from overhunting during the 1800s. Tule elk exhibited lower levels of heterozygosity (0.44 ± 0.03 [SD]) and allelic richness (2.9 ± 0.2) than Rocky Mountain (0.58 ± 0.05, 4.9 ± 0.4, respectively) and Roosevelt (0.50 ± 0.06, 4.4 ± 0.6, respectively) elk. Among tule elk populations, heterozygosity varied, with the lowest heterozygosity (0.23 ± 0.05) corresponding to the oldest enclosed herd used over the past century as a source of translocations. Among tule elk populations, genetic structure revealed several cases of successful and unsuccessful reintroduction or augmentation attempts. Results provide an essential baseline for future monitoring and decisions about harvest management, translocations to preserve genetic diversity, and landscape‐level conservation planning to maintain, enhance, or obstruct connectivity of elk populations. Genome‐wide sequencing and analyses are needed to quantify inbreeding absolutely and assess genetic load and the age of admixture where subspecies currently exchange genes.

Habitat suitability assessment for tule elk in the San Francisco Bay and Monterey Bay areas

While California’s statewide tule elk (Cervus canadensis nannodes) population has recovered from two or three individual survivors in the late 19th century, the subspecies exists today in numerous widely disjunct populations, leaving vast areas of the species’ former range uninhabited. Large unoccupied areas of historic tule elk range include the Santa Cruz Mountains and the northern Diablo and northern Santa Lucia ranges. Natural range expansion by existing populations into these areas is blocked by major highways and urban development; although, before considering tule elk translocations, it is necessary to assess the habitat suitability there. To this end, we fit a resource selection function (RSF) using generalized linear mixed models to GPS collar data collected from nearby radio collared tule elk and used several environmental GIS layers to capture important habitat characteristics. We fit the RSF in a habitat use versus availability framework with only linear and quadratic terms and used stepwise model selection ranked by AICc to maximize its generalizability, enabling transferability to our unoccupied study area. We also used k-fold cross validation to evaluate our RSF and found it predicted habitat within the San Luis Reservoir herd well. The fit habitat relationships mostly followed expectations based on tule elk ecology, including positive responses to herbaceous vegetation cover and waterbody proximity, and negative responses to high tree cover and high puma habitat suitability. Our RSF accurately predicted currently occupied elk habitat as suitable and found well over 500,000 ha (2,000 mi2) of suitable but unoccupied habitat throughout the northern Diablo Range, the inland and coastal sides of the Santa Cruz Mountains, and the northern Santa Lucia Range. Assuming translocations, and construction and improvement of highway wildlife crossings, our results support the potential for re-establishing tule elk in these regions, which are more coastal and mesic than the species’ current habitat in the central Diablo and northern Gabilan ranges.

Late Holocene tule elk (Cervus canadensis nannodes) resource depression and distant patch use in central California: Faunal and isotopic evidence from King Brown and the Emeryville Shellmound

Previous research has documented declines in the abundance of high-return resources including tule elk (Cervus canadensis nannodes) over the past three millennia in central California, suggesting the occurrence of resource depression. We test the hypothesis that hunting depressed tule elk in this setting by articulating stable isotope analyses from 88 directly dated tule elk specimens with data on the age structure and skeletal part representation from the King Brown and Emeryville Shellmound sites. Late Holocene trends in stable isotopes and modeled climatic variation are inconsistent with climate-based population declines. However, at King Brown, located within the Central Valley and vast tule elk freshwater marsh and grassland habitat, increasing isotopic diversity, a decline in mean age, and increasing abundance of high-utility skeletal elements suggest local depression stimulated the increasing use of distant elk patches. Although faunal trends are consistent with the depression of elk at Emeryville, the site is located on the shore of the San Francisco Bay where limited elk habitat existed, and no evidence of distant elk patch use is indicated. This analysis underscores how human behavioral responses to resource depression can vary in relation to the local ecology as they affect patch use economics for specific prey and demonstrates how such responses can be deciphered through stable isotope and faunal data.

Tule elk selection of surface water and forage is mediated by season and drought

Climate change is expected to affect arid-system ungulate populations by altering the distribution and availability of critical resources such as water and forage, particularly through more frequent and extreme droughts. Tule elk (Cervus canadensis nannodes), a subspecies of North American elk endemic to the Mediterranean climate regions of California, USA, can provide insight into the habitat selection behaviors arid-system ungulate populations use in response to changing resource availability. We used location data collected between 2005⁠–⁠2017 from GPS-collared tule elk to model elk response to surface water sources, forage dynamics (i.e., spatio-temporal changes in forage quality and abundance), and drought in the wet and dry seasons. These data spanned the extreme drought that occurred from 2012–⁠2017, a time when survival was apparently stable in the population. We found that, in the dry season, tule elk localized around water sources but selected areas farther from water with greater forage abundance. In the wet season, high quality forage and road avoidance were the primary factors influencing selection. These patterns were intensified by the extreme drought, with elk selecting areas closer to water in the dry season and farther from water sources in the wet season. Tule elk appeared to modify their behavior to minimize the impacts of drought on their survival. These findings suggest that water source availability and the relationship between water sources and other landscape features, including forage and roads, are a critical component of ungulate management in drought-prone regions.

Review of considerations for restoration of tule elk to the San Francisco Peninsula and northern Monterey Bay counties of California

Successful translocations of tule elk (Cervus canadensis nannodes) have been conducted since the early 1900s, with their state population rising from a nadir of as few as three surviving individuals to about 500 when reintroductions began, and to over 5,700 by 2017. However, natural range expansion of extant populations is currently limited by heavily trafficked major highways and urban areas with dense human populations. We determined that the San Francisco Peninsula and northern Monterey Bay counties (the study area) offer 193,973 ha (479,308 acres) of protected open space, several orders of magnitude greater than coastal tule elk home range size. Habitat suitability is supported by abundant historical observer, museum, and archeological records of elk located in this region. The nearest elk population to the study area is in eastern Santa Clara County and has grown from 65 animals that were translocated to Mt. Hamilton in the Diablo Range from 1978–1981 to at least 90 in five–six separate herds counted by aerial and photographic surveys in 2019. United States (U.S.) Highway 101 and metropolitan San Jose remain barriers to western range extension. Translocation and/or construction of freeway over- and under-crossings may enable westward range expansion to a less arid region, contributing to increased resilience of tule elk to climate change, and bringing aesthetic, financial, and ecological benefits of this once native ungulate grazer to the area.

Use of aerial distance sampling to estimate abundance of tule elk across a gradient of canopy cover and comparison to a concurrent fecal DNA spatial capture-recapture survey

Historically, aerial surveys have been used widely to monitor abundance of large mammals in the western United States. In California, such surveys have typically served as minimum count indices rather than true abundance estimates. Here, we evaluated the utility of aerial multiple covariate distance sampling (MCDS) to estimate abundance of three populations of tule elk (Cervus canadensis nannodes) in northern California. We also compared estimates and costs with published results from a concurrent fecal DNA spatial capture-recapture (SCR) survey. During December 2018 and 2019, we flew line transects for distance sampling of tule elk in Colusa and Lake counties. We modeled detection functions and evaluated effects of group size, canopy cover, and survey year. We averaged the top models comprising ≥0.95 of Akaike Model Weight and estimated abundance of both total and discrete populations. Detection probability increased with increasing group size and decreasing canopy cover. We estimated a two-year average total population size of N̂ = 674 elk (90% CI = 501–907) in our survey area which was similar to N̂ = 653 elk (90% CI = 573–745) from SCR estimates. Overall precision was greater (CV = 0.08; range = 0.11–0.30 by population) for SCR than for MCDS (CV = 0.18; range = 0.22–0.43 by population). Although estimates differed somewhat between methods for the individual populations, the combined estimate across the study region compared favorably. Total cost of SCR and MCDS surveys was $98,326 and $147,324, respectively. While SCR efforts were more precise and less expensive overall, our MCDS approach reduced staff time by 64% (587 person-hours) and the number of survey days by 87% (64 days). Our results suggest MCDS methods can produce reliable abundance estimates across a gradient of canopy cover, particularly when observations can be pooled across populations to decrease variance. We recommend future research to assess use of hybrid models, such as mark-recapture distance sampling or hierarchical distance sampling, to improve precision and estimation of detection probability.

Robustness of fecal DNA spatial capture‐recapture to clustered space‐use by tule elk

AbstractSpatially explicit capture‐recapture (SCR) approaches using noninvasive fecal DNA (fDNA) are applied increasingly to obtain statistically robust abundance estimates for various wildlife species. But SCR has not been widely used for more gregarious species, such as elk (Cervus canadensis). Because of their heterogeneous use of the landscape and grouping behavior, elk present novel challenges to sampling efficiency and statistical assumptions. We employed fDNA SCR and a stratified random sampling approach to estimate abundance in 3 northern California tule elk (C. c. nannodes) populations concurrent with global positioning system (GPS)‐telemetry monitoring of 66 elk (32 male, 34 female) in Colusa and Lake counties, California, USA, during June–August 2017–2019. We collected 1,616 fecal pellet groups from the 3 populations, resulting in 1,002 fDNA genotypes (≥19 microsatellite loci, 1 sex marker) of 425 unique individuals. Based on SCR estimates from a model incorporating both sexes, elk density ranged from 0.31 (95% CI = 0.17–0.55) elk/km2to 1.7 (95% CI = 1.3–2.2) elk/km2, translating approximately to 650 individuals (evenly split between sexes) among the 3 populations. Independent telemetry data from concurrently tracked individuals indicated that activity centers of females, but not males, were clustered on the landscape. This finding was corroborated using fDNA to infer activity centers. Comparison of SCR estimates to non‐spatial estimates using physically captured individuals suggested that combined‐sex SCR models were robust to spatial clustering of females in all 3 populations. Additionally, single‐sex models were robust to female clustering in the 2 populations with multiple female groups, but not in Lake Pillsbury, where all females effectively shared a single activity center. In that case, the estimate of female abundance was deemed an overestimate. Thus, results indicate that SCR was robust to gregariousness in elk in all but the most extreme cases of clustering (single‐sex female estimation when all individuals share a single activity center), and that the inclusion of both sexes was sufficient to offset biases stemming from aggregation of females in all cases. Altogether, our findings suggest that SCR methods can be gainfully applied to socially gregarious ungulates such as elk.

Testing a single-visit sampling approach for fecal DNA abundance estimation of tule elk in the Lake Pillsbury Basin

Testing a single-visit sampling approach for fecal DNA abundance estimation of tule elk in the Lake Pillsbury Basin

Mitigating anthropogenic barriers to facilitate distributional shifts helps reduce vulnerability of a large herbivore to climate change

AbstractClimate change is among the greatest threats to biodiversity conservation worldwide. Understanding which species are vulnerable to climate change and in what ways is essential for adaptation planning and mitigation. We used the NatureServe Climate Change Vulnerability Index (CCVI) to conduct a range‐wide assessment of tule elk (Cervus canadensis nannodes) – a California‐endemic ungulate with low genetic diversity, occupying highly fragmented landscapes – to climate change. Using results from the CCVI, we tested the hypothesis that increasing connectivity among populations, by mitigating anthropogenic barriers to movement and dispersal, decreases vulnerability of tule elk to climate change. We compared CCVI scores given predicted conditions within current ranges with CCVI scores as if anthropogenic barriers were mitigated, with and without allowing elk to shift distributions up to 50 km to areas predicted to experience less warming, drying, or overall exposure to climate change (indicated by an interaction between warming and drying). Vulnerability of tule elk to climate change varied among populations; from most to least vulnerable rankings in the CCVI, 1 population was ranked extremely vulnerable, 1 was highly vulnerable, 12 were moderately vulnerable, and 4 were less vulnerable. Mitigating anthropogenic barriers alone did not have a significant effect on vulnerability to climate change compared to original CCVI estimates, nor did mitigation of anthropogenic barriers and shifts in distribution to areas expected to experience the least amount of warming. Mitigation of anthropogenic barriers coupled with elk shifting distributions to areas predicted to experience less drying than current ranges or less overall exposure to climate change significantly reduced climate change vulnerability. Our findings illustrate the need to prioritize increasing landscape connectivity for tule elk across California as part of climate change mitigation measures, but also may apply to non‐migratory ungulates more generally, particularly where drying and warming are predicted to increase under climate change.

Assessing genetic diversity and connectivity in a tule elk (Cervus canadensis nannodes) metapopulation in Northern California

The tule elk (Cervus canadensis nannodes) is a California endemic subspecies that experienced an extreme bottleneck (potentially two individuals) in the mid-1800s. Through active management, including reintroductions, the subspecies has grown to approximately 6000 individuals spread across 22 recognized populations. The populations tend to be localized and separated by unoccupied intervening habitat, prompting targeted translocations to ensure gene flow. However, little is known about the genetic status or connectivity among adjacent populations in the absence of active translocations. We used 19 microsatellites and a sex marker to obtain baseline data on the genetic effective population sizes and functional genetic connectivity of four of these populations, three of which were established since the 1980s and one of which was established ~ 100 years ago. A Bayesian assignment approach suggested the presence of 5 discrete genetic clusters, which corresponded to the four primary populations and two subpopulations within the oldest of them. Effective population sizes ranged from 15 (95% CI 10–22) to 51 (95% CI 32–88). We detected little or no evidence of gene flow among most populations. Exceptions were a signature of unidirectional gene flow to one population founded by emigrants of the other 30 years earlier, and bidirectional gene flow between subpopulations within the oldest population. We propose that social cohesion more than landscape characteristics explained population structure, which developed over many generations corresponding to population expansion. Whether or which populations can grow and reach sufficient effective population sizes on their own or require translocations to maintain genetic diversity and population growth is unclear. In the future, we recommend pairing genetic with demographic monitoring of these and other reintroduced elk populations, including targeted monitoring following translocations to evaluate their effects and necessity.

Effects of human-altered landscapes on a reintroduced ungulate: Patterns of habitat selection at the rangeland-wildland interface

Successful species reintroductions require land managers to balance the goal of viable wildlife populations with potential risks to human enterprise. Such risks are particularly acute at the wildland-agriculture interface, where native and domestic species are likely to come into contact. In a national park in northern California, we combined insights from three lines of evidence – long-term visual surveys, short-term GPS telemetry, and satellite remote sensing-based animal detections – to characterize spatial overlap between reintroduced tule elk (Cervus canadensis nannodes) and domestic cattle and to estimate the importance of multiple environmental features as predictors of habitat selection by elk. Our results indicate that, at large spatial scales (i.e., home-range level), cattle were the primary driver of habitat selection, with the occurrence of elk being negatively associated with cattle across all seasons. In addition, elk consistently selected for grasslands on gentle, south-facing slopes that occurred at high elevation and close to ponds. NDVI was a seasonally important, positive predictor of habitat selection, with a marked reversal when this resource was concentrated inside of fenced cow pastures during the dry summer months. By contrast, a novel analysis of satellite-derived animal locations yielded no evidence of avoidance of cattle by elk (within pasture areas commonly used by elk), indicating that this population has acclimated to the presence of cattle through spatial partitioning of resources. Thus, this once-imperiled native ungulate exhibits patterns of habitat selection that reduce the potential for grazing conflicts with cattle, even in cases where access to forage is limited.

A panel of 96 SNPs to identify individuals and differentiate subspecies of elk (Cervus canadensis) for microfluidic and other genotyping platforms

The tule elk (Cervus canadensis nannodes) is endemic to California, USA, where it experienced an extreme genetic bottleneck in the 1870s. Two other subspecies of elk co-occur in California, Roosevelt (C. c. roosevelti) and Rocky Mountain (C. c. nelsoni) elk. These subspecies potentially interbreed in contact zones. For monitoring and genetic management of fragmented populations, markers are needed to differentiate both individuals and subspecies. Using Illumina HiSeq sequencing of 12 individuals, including four from each subspecies, we developed a suite of 96 SNP markers for a Fluidigm platform. This marker set enabled differentiation of individuals and subspecies with high confidence and will facilitate genetic monitoring of elk throughout their range.

Whole-genome sequencing of Tarim red deer (Cervus elaphus yarkandensis) reveals demographic history and adaptations to an arid-desert environment

BackgroundThe initiation of desert conditions in the Tarim Basin in China since the late Miocene has led to the significant genetic structuring of local organisms. Tarim Red Deer (Cervus elaphus yarkandensis, TRD) have adapted to the harsh environmental conditions in this basin, including high solar radiation and temperature, aridity, and poor nutritional conditions. However, the underlying genetic basis of this adaptation is poorly understood.ResultsWe sequenced the whole genomes of 13 TRD individuals, conducted comparative genomic analyses, and estimated demographic fluctuation. The ∂a∂i model estimated that the TRD and Tule elk (Cervus canadensis nannodes) populations diverged approximately 0.98 Mya. Analyses revealed a substantial influence of the Earth’s climate on the effective population size of TRD, associated with glacial advances and retreat, and human activities likely underlie a recent serious decline in population. A marked bottleneck may have profoundly affected the genetic diversity of TRD populations. We detected a set of candidate genes, pathways, and GO categories related to oxidative stress, water reabsorption, immune regulation, energy metabolism, eye protection, heat stress, respiratory system adaptation, prevention of high blood pressure, and DNA damage and repair that may directly or indirectly be involved in the adaptation of TRD to an arid-desert environment.ConclusionsOur analyses highlight the role of historical global climates in the population dynamics of TRD. In light of ongoing global warming and the increasing incidence of droughts, our study offers insights into the genomic adaptations of animals, especially TRD, to extreme arid-desert environments and provides a valuable resource for future research on conservation design and biological adaptations to environmental change.

Context-dependent effects of a reintroduced ungulate on soil properties are driven by soil texture, moisture, and herbivore activity.

Although there is considerable evidence that large mammalian herbivores influence ecosystem‐level processes, studies have reported such widely varying results that generalizations have remained elusive. Here, we use an 18‐year‐old exclosure experiment—stratified across a landscape heterogeneous with respect to soil texture, moisture and herbivore activity—to understand the variable effects of tule elk (Cervus canadensis nannodes), a native reintroduced herbivore, on soil properties along the coast of northern California. Elk significantly increased soil bulk density and created a compacted layer at shallow soil depth, while decreasing infiltration rate and pH. The effects of elk on bulk density, penetration resistance, and pH varied with soil type, being least pronounced in coarse, sandy loams, and greatest in loose sand. The effects of elk on nutrient availability varied along gradients of soil texture and moisture. In coarser soils, elk decreased ammonium availability, but increased it in finer soils. Elk also decreased soil moisture content, in part through their positive effect on bulk density, and this effect was most pronounced in coarser soils. Through decreasing soil moisture content, elk also decreased nitrate availability in coarser soils. At greater levels of elk activity (as measured by dung deposition), the elk effect on bulk density was amplified, and this had a corresponding negative effect on nitrate and phosphate availability. Our study has demonstrated that a better understanding of spatial variation in the effects of herbivores on ecosystems can emerge by evaluating their influences across gradients of soil texture, soil moisture, and herbivore activity. These data enabled us to evaluate several frameworks that have been developed to understand the variable effects of herbivores on ecosystems, which is a significant step in reconciling the many competing ideas put forth to explain the context‐dependent effects of large herbivores on grazed ecosystems.

The complete mitochondrial genome of Cervus canadensis (Erxleben, 1777), as a model species of Chronic Wasting Disease (CWD)

Cervus canadensis (Erxleben, 1777) has been used as a model species of Chronic Wasting Disease (CWD). We completed the mitochondrial genome of C. canadensis, susceptible to the CWD. Its length is 16,428 bp, identical to the previous mitochondrial genome of C. canadensis nannodes, and 37 genes (13 protein-coding genes, two rRNAs, and 22 tRNAs) were identified. It may reflect the extreme decrease of tule elk population in 1870s and CWD is not related to genetic elements on mitochondrial genome. Phylogenetic trees show that our mitochondrial genome is clustered with the previously sequenced mitochondrial genome of C. canadensis nannodes .

The first complete mitogenome of Cervus canadensis nannodes (Merriam, 1905)

Cervus canadensis nannodes (Merriam, 1905) is one of the subspecies of elk distributed only in California, USA. We completed the first mitogenome of C. canadensis nannodes. Its length is 16,428 bp, which is in middle among 24 available Cervus mitogenomes. It contains 37 genes (13 protein-coding genes, 2 rRNAs, and 22 tRNAs). Phylogenetic trees show that C. c. nannodes was clustered with some subspecies of C. elaphus. Number of inter-subspecific variations between C. c. nannodes and C. e. alxaicus are relatively small in comparison to intraspecific variations of insect and fish mitogenomes and plant chloroplast genomes.

Cascading effects of mammalian herbivores on ground-dwelling arthropods: Variable responses across arthropod groups, habitats and years.

Large mammalian herbivores are well known to shape the structure and function of ecosystems world-wide, and these effects can in turn cascade through systems to indirectly influence other animal species. A wealth of studies has explored the effects of large mammals on arthropods, but to date they have reported such widely varying results that generalizations have been elusive. Three factors are likely drivers of this variability: the widely varying life-history characteristics of different arthropod groups, the highly variable landscapes that mammalian herbivores commonly inhabit and temporal variation in environmental conditions. Here, we use an 18-year-old exclosure experiment stratified across three distinct coastal prairie habitats in northern California to address the effects of a reintroduced mammalian herbivore, tule elk (Cervus canadensis nannodes) on the composition, richness and abundance of ground-dwelling arthropods over two years with very different precipitation regimes. We found that elk shifted the composition of arthropod communities, increasing the abundance of ants, beetles, spiders and mites, decreasing the abundance of woodlice and bristletails in some but not all habitats types, and having no effect on the abundance of bugs, crickets and springtails. Elk also increased richness and changed the composition of ant genera and beetle morpho-species. Interestingly, the effects of elk on arthropod composition, richness and abundance varied little between years, despite very different precipitation levels, biomass accumulation and thatch height. Elk reduced shrub cover, above-ground herbaceous biomass and thatch height and increased soil compaction, and these changes predicted the abundance and richness of arthropods, although taxonomic groups varied in their responses, presumably due to differences in environmental requirements. Synthesis. Our research highlights the importance of using long-term experiments to assess the cascading effects of large herbivores on the composition of grounddwelling arthropod communities and to identify the mechanisms that indirectly shape arthropod responses to herbivores among variable habitats and years in order to develop a greater understanding of the variable responses of arthropods to large mammalian herbivores.

Indirect effects of a large mammalian herbivore on small mammal populations: Context-dependent variation across habitat types, mammal species, and seasons.

Multiple consumer species frequently co‐occur in the same landscape and, through effects on surrounding environments, can interact in direct and indirect ways. These interactions can vary in occurrence and importance, and focusing on this variation is critical for understanding the dynamics of interactions among consumers. Large mammalian herbivores are important engineers of ecosystems worldwide, have substantial impacts on vegetation, and can indirectly affect small‐mammal populations. However, the degree to which such indirect effects vary within the same system has received minimal attention. We used a 16‐year‐old exclosure experiment, stratified across a heterogeneous landscape, to evaluate the importance of context‐dependent interactions between tule elk (Cervus canadensis nannodes) and small mammals (deer mice [Peromyscus maniculatus], meadow voles [Microtus californicus], and harvest mice [Reithrodontymys megalotis]) in a coastal grassland in California. Effects of elk on voles varied among habitats and seasons: In open grasslands, elk reduced vole numbers during fall 2013 but not summer 2014; in Lupinus‐dominated grasslands, elk reduced vole numbers during summer 2014 but not fall 2013; and in Baccharis‐dominated grasslands, elk had no effect on vole numbers in either season. Effects of elk on the two mice species also varied among habitats and seasons, but often in different ways from voles and each other. In fall 2013, elk decreased mice abundances in Lupinus‐dominated grasslands, but not in Baccharis‐dominated or open grasslands. In summer 2014, elk decreased the abundance of harvest mice consistently across habitat types. In contrast, elk increased deer‐mice numbers in open grasslands but not other habitats. Within the same heterogenous study system, the influence of elk on small mammals was strongly context‐dependent, varying among habitats, mammal species, and seasons. We hypothesize that such variability is common in nature and that failure to consider it may yield inaccurate findings and limit our understanding of interactions among co‐occurring consumers.

Hope and caution: rewilding to mitigate the impacts of biological invasions.

Rewilding is a novel approach to ecological restoration. Trophic rewilding in particular aims to reinstate ecological functions, especially trophic interactions, through the introduction of animals. We consider the potential for trophic rewilding to address biological invasions. In this broad review, we note some of the important conceptual and ethical foundations of rewilding, including a focus on ecosystem function rather than composition, reliance on animal agency, and an appeal to an ethic of coexistence. Second, we use theory from invasion biology to highlight pathways by which rewilding might prevent or mitigate the impacts of an invasion, including increasing biotic resistance. Third, we use a series of case studies to illustrate how reintroductions can mitigate the impacts of invasions. These include reintroductions and positive management of carnivores and herbivores including European pine martens (Martes martes), Eurasian otters (Lutra lutra), dingoes (Canis dingo), Tasmanian devils (Sarcophilus harrisii) and tule elk (Cervus canadensis nannodes). Fourth, we consider the risk that rewilding may enable a biological invasion or aggravate its impacts. Lastly, we highlight lessons that rewilding science might take from invasion biology.This article is part of the theme issue 'Trophic rewilding: consequences for ecosystems under global change'.

Pests and Politics: Managing Free-Ranging Tule Elk in Point Reyes National Seashore

In 1978, Point Reyes National Seashore (PRNS) reintroduced Tule elk, which is the only National Park unit where Tule elk can be found. The State of California provided the initial elk Tomales Point in PRNS. State wildlife biologists were members of the team that managed the re-introduction and subsequent monitoring. Tomales Point is a fenced area; however, one goal of the 1998 Tule Elk Management Plan was to establish a free-ranging Tule elk herd to the seashore. That plan stated the forage is unaffected by the number of elk occupying the range and elk do not have a strictly negative effect on vegetation. However, in 1999, PRNS moved a free-range herd of 28 elk from Tomales Point to the wilderness area near Limantour Beach. Within weeks, a few elk unexpectedly migrated to ranches in the designated pastoral zone. Currently, Drakes Beach (D Ranch) herd includes approximately 150 Tule elk. Designated pastoral zone, where livestock and dairy producer operations may be permitted, are charged an annual lease based on the lands’ carrying capacity. In 2004, beef and dairy producers began to express concerns about the impacts elk were having on forage, organic certifications, and overall economic viability. In 2014, PRNS initiated the Ranch Comprehensive Management Plan to assess growing concerns of beef and dairy producers related to the free-ranging elk impacts to the pastoral zone. PRNS staff have not implemented any of their 1998 control methods, and are currently only hazing elk away from permitted operations. The efficacy of hazing elk away from the pastoral zone is in question; and PRNS has stated an inability to do more control due to recent litigation. Efforts should focus on non-lethal effective elk management options, such as contraception, which abide by current litigation constraints while mitigating producer burden and concern. The objective of this paper is to develop a case for potential multi-species management (i.e., elk plus cattle) at PRNS while protecting its historical, biodiversity, and economic value.