Aspen recovery in northern Yellowstone: A comment on Brice et al. (2021).

Aspen sapling recruitment increased as browsing by elk decreased, following the 1995-96 reintroduction of wolves in Yellowstone National Park. We address claims by Brice et al. (2021) that previous studies exaggerated recent aspen recovery. We conclude that their results actually supported previous work showing a trophic cascade benefiting aspen.

The influence of social identity on attitudes toward wildlife.

Wildlife conservation depends on supportive social as well as biophysical conditions. Social identities such as hunter and nonhunter are often associated with different attitudes toward wildlife. However, it is unknown whether dynamics within and among these identity groups explain how attitudes form and why they differ. To investigate how social identities help shape wildlife-related attitudes and the implications for wildlife policy and conservation, we built a structural equation model with survey data from Montana (USA) residents (n = 1758) that tested how social identities affect the relationship between experiences with grizzly bears (Ursus arctos horribilis) and attitudes toward the species. Model results (r2 = 0.51) demonstrated that the hunter identity magnified the negative effect of vicarious property damage on attitudes toward grizzly bears (ß = -0.381, 95% confidence interval [CI]: -0.584 to -0.178, p < 0.001), which in turn strongly influenced acceptance (ß = -0.571, 95% CI: -0.611 to -0.531, p < 0.001). Our findings suggested that hunters' attitudes toward grizzly bears likely become more negative primarily because of in-group social interactions about negative experiences, and similar group dynamics may lead nonhunters to disregard the negative experiences that out-group members have with grizzly bears. Given the profound influence of social identity on human cognitions and behaviors in myriad contexts, the patterns we observed are likely important in a variety of wildlife conservation situations. To foster positive conservation outcomes and minimize polarization, management strategies should account for these identity-driven perceptions while prioritizing conflict prevention and promoting positive wildlife narratives within and among identity groups. This study illustrates the utility of social identity theory for explaining and influencing human-wildlife interactions.

La influencia de la identidad social sobre la actitud hacia la fauna Resumen La conservación de la fauna depende de condiciones de apoyo tanto sociales como biofísicas. La identidad social, como ser cazador o no, con frecuencia está asociada a las diferentes actitudes hacia la fauna. Sin embargo, no sabemos si las dinámicas dentro y entre estos grupos de identidad explican cómo las actitudes se forman y porqué son diferentes. Construimos un modelo de ecuación estructural con información de encuestas realizadas a 1,758 residentes de Montana (Estados Unidos) para conocer cómo la identidad social ayuda a formar la actitud relacionada con la fauna y las implicaciones que tiene para la conservación y políticas de fauna. El modelo analizó cómo la identidad social afecta la relación entre las experiencias con osos pardos (Ursus arctos horribilis) y la actitud hacia la especie. Los resultados del modelo (r2 = 0.51) demostraron que la identidad de cazador aumentaba el efecto negativo del daño indirecto a la propiedad sobre la actitud hacia los osos (ß=­0.381, 95% CI ­0.584 a ­0.178, p<0.001), lo cual en cambio tenía una gran influencia sobre la aceptación (ß=­0.571, 95% CI ­0.611 a ­0.531, p<0.001). Nuestros descubrimientos sugieren que la actitud de los cazadores hacia los osos probablemente se vuelve más negativa principalmente debido a las interacciones sociales del endogrupo en torno a las experiencias negativas; las dinámicas similares pueden llevar a los no cazadores a menospreciar las experiencias negativas que los miembros del exogrupo han tenido con los osos. Dada la influencia profunda que tiene la identidad social sobre la cognición humana y el comportamiento en una miríada de contextos, los patrones que observamos probablemente sean importantes en una variedad de situaciones de conservación de fauna. Para promover los resultados positivos de conservación y minimizar la polarización, las estrategias de manejo deberían considerar estas percepciones influenciadas por la identidad mientras se prioriza la prevención de conflictos y se promueven narrativas positivas de fauna dentro y entre los grupos de identidad. Este estudio demuestra la utilidad que tiene la teoría de identidad social para explicar e influenciar las interacciones humano­fauna.

The 2018 reawakening and eruption dynamics of Steamboat Geyser, the world's tallest active geyser.

Steamboat Geyser in Yellowstone National Park's Norris Geyser Basin began a prolific sequence of eruptions in March 2018 after 34 y of sporadic activity. We analyze a wide range of datasets to explore triggering mechanisms for Steamboat's reactivation and controls on eruption intervals and height. Prior to Steamboat's renewed activity, Norris Geyser Basin experienced uplift, a slight increase in radiant temperature, and increased regional seismicity, which may indicate that magmatic processes promoted reactivation. However, because the geothermal reservoir temperature did not change, no other dormant geysers became active, and previous periods with greater seismic moment release did not reawaken Steamboat, the reason for reactivation remains ambiguous. Eruption intervals since 2018 (3.16 to 35.45 d) modulate seasonally, with shorter intervals in the summer. Abnormally long intervals coincide with weakening of a shallow seismic source in the geyser basin's hydrothermal system. We find no relation between interval and erupted volume, implying unsteady heat and mass discharge. Finally, using data from geysers worldwide, we find a correlation between eruption height and inferred depth to the shallow reservoir supplying water to eruptions. Steamboat is taller because water is stored deeper there than at other geysers, and, hence, more energy is available to power the eruptions.

A metapopulation model of social group dynamics and disease applied to Yellowstone wolves.

The population structure of social species has important consequences for both their demography and transmission of their pathogens. We develop a metapopulation model that tracks two key components of a species' social system: average group size and number of groups within a population. While the model is general, we parameterize it to mimic the dynamics of the Yellowstone wolf population and two associated pathogens: sarcoptic mange and canine distemper. In the initial absence of disease, we show that group size is mainly determined by the birth and death rates and the rates at which groups fission to form new groups. The total number of groups is determined by rates of fission and fusion, as well as environmental resources and rates of intergroup aggression. Incorporating pathogens into the models reduces the size of the host population, predominantly by reducing the number of social groups. Average group size responds in more subtle ways: infected groups decrease in size, but uninfected groups may increase when disease reduces the number of groups and thereby reduces intraspecific aggression. Our modeling approach allows for easy calculation of prevalence at multiple scales (within group, across groups, and population level), illustrating that aggregate population-level prevalence can be misleading for group-living species. The model structure is general, can be applied to other social species, and allows for a dynamic assessment of how pathogens can affect social structure and vice versa.

Peeking under the canopy: anomalously short fire-return intervals alter subalpine forest understory plant communities.

Climate change is driving changes in disturbance regimes world-wide. In forests adapted to infrequent, high-severity fires, recent anomalously short fire-return intervals (FRIs) have resulted in greatly reduced postfire tree regeneration. However, effects on understory plant communities remain unexplored. Understory plant communities were sampled in 31 plot pairs across Greater Yellowstone (Wyoming, USA). Each pair included one plot burned at high severity twice in < 30 yr and one plot burned in the same most recent fire but not burned previously for > 125 yr. Understory communities following short-interval fires were also compared with those following the previous long-interval fire. Species capable of growing in drier conditions and in lower vegetation zones became more abundant and regional differences in plant communities declined following short-interval fire. Dissimilarity between plot pairs increased in mesic settings and decreased with time since fire and postfire winter snowfall. Reduced postfire tree density following short-interval fire rather than FRI per se affected the occurrence of most plant species. Anomalously short FRIs altered understory plant communities in space and time, with some indications of community thermophilization and regional homogenization. These and other shifts in understory plant communities may continue with ongoing changes in climate and fire across temperate forests.

Using social-ecological models to explore stream connectivity outcomes for stakeholders and Yellowstone cutthroat trout.

Despite growing interest in conservation and re-establishment of ecological connectivity, few studies have explored its context-specific social-ecological outcomes. We aimed to explore social and ecological outcomes to changing stream connectivity for both stakeholders and native fish species impacted by habitat fragmentation and nonnative species. We (1) investigated stakeholder perceptions of the drivers and outcomes of stream connectivity, and (2) evaluated the effects of stakeholder-identified connectivity and nonnative species scenarios on Yellowstone cutthroat trout (YCT) populations. Our study was conducted in the Teton River, Idaho, USA. We integrated two modeling approaches, mental modeling and individual-based ecological modeling, to explore social-ecological outcomes for stakeholders and YCT populations. Aggregation of mental models revealed an emergent pattern of increasing complexity as more types of stakeholders were considered, as well as gaps and linkages among different stakeholder knowledge areas. These results highlight the importance of knowledge sharing among stakeholders when making decisions about connectivity. Additionally, the results from the individual-based models suggested that the potential for a large, migratory life history form of YCT, in addition to self-preference mating where they overlap with rainbow trout, had the strongest effects on outcomes for YCT. Exploring social and ecological drivers and outcomes to changing connectivity is useful for anticipating and adapting to unintended outcomes, as well as making decisions for desirable outcomes. The results from this study can contribute to the management dialogue surrounding stream connectivity in the Teton River, as well as to our understanding of connectivity conservation and its outcomes more broadly.

Feast or famine: How is global change affecting forage supply for Yellowstone's ungulate herds?

The ecological integrity of US national parks and other protected areas are under threat in the Anthropocene. For Yellowstone National Park (YNP), the impacts that global change has already had on the park's capacity to sustain its large migratory herds of wild ungulates is incompletely understood. Here we examine how two understudied components of global change, the historical increase in atmospheric CO2 and the spread of nonnative, invasive plant species, may have altered the capacity of YNP to provide forage for ungulates over the last 200-plus years. We performed two experiments: (1) a growth chamber study that determined the growth rates of important invasive and native YNP grasses that are forages for ungulates under preindustrial (280 ppm) versus modern (410 ppm) CO2 levels and (2) a field study that compared the effect of defoliation (clipping) on the shoot growth of invasive and native mesic grassland plants under ambient CO2 conditions in 2019. The growth chamber experiment revealed that modern CO2 increased the growth rates of both invasive and native grasses, and invasive grasses grew faster regardless of CO2 conditions. The field results showed a continuum of positive to negative responses of shoot growth to defoliation, with a subgroup of invasive species responding most positively. Altogether the results indicated that the historical increase in CO2 and the spread of invasive species, some of which were planted to provide forage for ungulates in the early and mid-1900s, have likely increased the capacity of forage production in YNP. However, rising CO2 has also resulted in regional warming and increased aridity in YNP, which will likely reduce grassland productivity. The challenge for global change biologists and park managers is to determine how competing components of global change have already affected and will increasingly affect forage dynamics and the sustainability of Yellowstone's iconic ungulate herds in the Anthropocene.

Identification of chondritic krypton and xenon in Yellowstone gases and the timing of terrestrial volatile accretion.

Identifying the origin of noble gases in Earth's mantle can provide crucial constraints on the source and timing of volatile (C, N, H2O, noble gases, etc.) delivery to Earth. It remains unclear whether the early Earth was able to directly capture and retain volatiles throughout accretion or whether it accreted anhydrously and subsequently acquired volatiles through later additions of chondritic material. Here, we report high-precision noble gas isotopic data from volcanic gases emanating from, in and around, the Yellowstone caldera (Wyoming, United States). We show that the He and Ne isotopic and elemental signatures of the Yellowstone gas requires an input from an undegassed mantle plume. Coupled with the distinct ratio of 129Xe to primordial Xe isotopes in Yellowstone compared with mid-ocean ridge basalt (MORB) samples, this confirms that the deep plume and shallow MORB mantles have remained distinct from one another for the majority of Earth's history. Krypton and xenon isotopes in the Yellowstone mantle plume are found to be chondritic in origin, similar to the MORB source mantle. This is in contrast with the origin of neon in the mantle, which exhibits an isotopic dichotomy between solar plume and chondritic MORB mantle sources. The co-occurrence of solar and chondritic noble gases in the deep mantle is thought to reflect the heterogeneous nature of Earth's volatile accretion during the lifetime of the protosolar nebula. It notably implies that the Earth was able to retain its chondritic volatiles since its earliest stages of accretion, and not only through late additions.

Flowering time advances since the 1970s in a sagebrush steppe community: Implications for management and restoration.

Climate change is widely known to affect plant phenology, but little is known about how these impacts manifest in the widespread sagebrush ecosystem of the Western United States, which supports a number of wildlife species of concern. Shifts in plant phenology can trigger consequences for the plants themselves as well as the communities of consumers that depend upon them. We assembled historical observations of first-flowering dates for 51 species collected in the 1970s and 1980s in a montane sagebrush community in the Greater Yellowstone Ecosystem and compared these to contemporary phenological observations targeting the same species and locations (2016-2019). We also assembled regional climate data (average spring temperature, day of spring snowmelt, and growing degree days) and tested the relationship between first-flowering time and these variables for each species. We observed the largest change in phenology in early-spring flowers, which, as a group, bloomed on average 17 days earlier, and as much as 36 days earlier, in the contemporary data set. Mid-summer flowers bloomed on average 10 days earlier, nonnative species 15 days earlier, and berry-producing shrubs 5 days earlier, while late summer flowering plants did not shift. The greatest correlates of early-spring and mid-summer flowering were average spring temperature and day of snowmelt, which was 21 days earlier, on average, in 2016-2019 relative to the 1973-1978 observations. The shifts in flowering phenology that we observed could indicate developing asynchronies or novel synchronies of these plant resources and wildlife species of conservation concern, including Greater Sage-grouse, whose nesting success is tied to availability of spring forbs; grizzly bears, which rely heavily on berries for their fall diet; and pollinators. This underscores the importance of maintaining a diverse portfolio of native plants in terms of species composition, genetics, phenological responsiveness to climatic cues, and ecological importance to key wildlife and pollinator species. Redundancy within ecological niches may also be important considering that species roles in the community may shift as climate change affects them differently. These considerations are particularly relevant to restoration and habitat-enhancement projects in sagebrush communities across western North America.

Short-interval severe fire erodes the resilience of subalpine lodgepole pine forests.

Subalpine forests in the northern Rocky Mountains have been resilient to stand-replacing fires that historically burned at 100- to 300-year intervals. Fire intervals are projected to decline drastically as climate warms, and forests that reburn before recovering from previous fire may lose their ability to rebound. We studied recent fires in Greater Yellowstone (Wyoming, United States) and asked whether short-interval (<30 years) stand-replacing fires can erode lodgepole pine (Pinus contorta var. latifolia) forest resilience via increased burn severity, reduced early postfire tree regeneration, reduced carbon stocks, and slower carbon recovery. During 2016, fires reburned young lodgepole pine forests that regenerated after wildfires in 1988 and 2000. During 2017, we sampled 0.25-ha plots in stand-replacing reburns (n = 18) and nearby young forests that did not reburn (n = 9). We also simulated stand development with and without reburns to assess carbon recovery trajectories. Nearly all prefire biomass was combusted ("crown fire plus") in some reburns in which prefire trees were dense and small (≤4-cm basal diameter). Postfire tree seedling density was reduced sixfold relative to the previous (long-interval) fire, and high-density stands (>40,000 stems ha-1) were converted to sparse stands (<1,000 stems ha-1). In reburns, coarse wood biomass and aboveground carbon stocks were reduced by 65 and 62%, respectively, relative to areas that did not reburn. Increased carbon loss plus sparse tree regeneration delayed simulated carbon recovery by >150 years. Forests did not transition to nonforest, but extreme burn severity and reduced tree recovery foreshadow an erosion of forest resilience.

Ecological Dichotomies Arise in Microbial Communities Due to Mixing of Deep Hydrothermal Waters and Atmospheric Gas in a Circumneutral Hot Spring.

Little is known of how the confluence of subsurface and surface processes influences the assembly and habitability of hydrothermal ecosystems. To address this knowledge gap, the geochemical and microbial composition of a high-temperature, circumneutral hot spring in Yellowstone National Park was examined to identify the sources of solutes and their effect on the ecology of microbial inhabitants. Metagenomic analysis showed that populations comprising planktonic and sediment communities are archaeal dominated, are dependent on chemical energy (chemosynthetic), share little overlap in their taxonomic composition, and are differentiated by their inferred use of/tolerance to oxygen and mode of carbon metabolism. The planktonic community is dominated by putative aerobic/aerotolerant autotrophs, while the taxonomic composition of the sediment community is more evenly distributed and comprised of anaerobic heterotrophs. These observations are interpreted to reflect sourcing of the spring by anoxic, organic carbon-limited subsurface hydrothermal fluids and ingassing of atmospheric oxygen that selects for aerobic/aerotolerant organisms that have autotrophic capabilities in the water column. Autotrophy and consumption of oxygen by the planktonic community may influence the assembly of the anaerobic and heterotrophic sediment community. Support for this inference comes from higher estimated rates of genome replication in planktonic populations than sediment populations, indicating faster growth in planktonic populations. Collectively, these observations provide new insight into how mixing of subsurface waters and atmospheric oxygen create dichotomy in the ecology of hot spring communities and suggest that planktonic and sediment communities may have been less differentiated taxonomically and functionally prior to the rise of oxygen at ∼2.4 billion years ago (Gya). IMPORTANCE Understanding the source and availability of energy capable of supporting life in hydrothermal environments is central to predicting the ecology of microbial life on early Earth when volcanic activity was more widespread. Little is known of the substrates supporting microbial life in circumneutral to alkaline springs, despite their relevance to early Earth habitats. Using metagenomic and informatics approaches, water column and sediment habitats in a representative circumneutral hot spring in Yellowstone were shown to be dichotomous, with the former largely hosting aerobic/aerotolerant autotrophs and the latter primarily hosting anaerobic heterotrophs. This dichotomy is attributed to influx of atmospheric oxygen into anoxic deep hydrothermal spring waters. These results indicate that the ecology of microorganisms in circumneutral alkaline springs sourced by deep hydrothermal fluids was different prior to the rise of atmospheric oxygen ∼2.4 Gya, with planktonic and sediment communities likely to be less differentiated than contemporary circumneutral hot springs.

Widespread regeneration failure in forests of Greater Yellowstone under scenarios of future climate and fire.

Changing climate and disturbance regimes are increasingly challenging the resilience of forest ecosystems around the globe. A powerful indicator for the loss of resilience is regeneration failure, that is, the inability of the prevailing tree species to regenerate after disturbance. Regeneration failure can result from the interplay among disturbance changes (e.g., larger and more frequent fires), altered climate conditions (e.g., increased drought), and functional traits (e.g., method of seed dispersal). This complexity makes projections of regeneration failure challenging. Here we applied a novel simulation approach assimilating data-driven fire projections with vegetation responses from process modeling by means of deep neural networks. We (i) quantified the future probability of regeneration failure; (ii) identified spatial hotspots of regeneration failure; and (iii) assessed how current forest types differ in their ability to regenerate under future climate and fire. We focused on the Greater Yellowstone Ecosystem (2.9 × 106  ha of forest) in the Rocky Mountains of the USA, which has experienced large wildfires in the past and is expected to undergo drastic changes in climate and fire in the future. We simulated four climate scenarios until 2100 at a fine spatial grain (100 m). Both wildfire activity and unstocked forest area increased substantially throughout the 21st century in all simulated scenarios. By 2100, between 28% and 59% of the forested area failed to regenerate, indicating considerable loss of resilience. Areas disproportionally at risk occurred where fires are not constrained by topography and in valleys aligned with predominant winds. High-elevation forest types not adapted to fire (i.e., Picea engelmannii-Abies lasiocarpa as well as non-serotinous Pinus contorta var. latifolia forests) were especially vulnerable to regeneration failure. We conclude that changing climate and fire could exceed the resilience of forests in a substantial portion of Greater Yellowstone, with profound implications for carbon, biodiversity, and recreation.

Quantifying energetic costs and defining energy landscapes experienced by grizzly bears.

Animal movements are major determinants of energy expenditure and ultimately the cost-benefit of landscape use. Thus, we sought to understand those costs and how grizzly bears (Ursus arctos) move in mountainous landscapes. We trained captive grizzly bears to walk on a horizontal treadmill and up and down 10% and 20% slopes. The cost of moving upslope increased linearly with speed and slope angle, and this was more costly than moving horizontally. The cost of downslope travel at slower speeds was greater than the cost of traveling horizontally but appeared to decrease at higher speeds. The most efficient walking speed that minimized cost per unit distance was 1.19±0.11 m s-1 However, grizzly bears fitted with GPS collars in the Greater Yellowstone Ecosystem moved at an average velocity of 0.61±0.28 m s-1 and preferred to travel on near-horizontal slopes at twice their occurrence. When traveling uphill or downhill, grizzly bears chose paths across all slopes that were ∼54% less steep and costly than the maximum available slope. The net costs (J kg-1 m-1) of moving horizontally and uphill were the same for grizzly bears, humans and digitigrade carnivores, but those costs were 46% higher than movement costs for ungulates. These movement costs and characteristics of landscape use determined using captive and wild grizzly bears were used to understand the strategies that grizzly bears use for preying on large ungulates and the similarities in travel between people and grizzly bears that might affect the risk of encountering each other on shared landscapes.

Investigating the Dynamics of Elk Population Size and Body Mass in a Seasonal Environment Using a Mechanistic Integral Projection Model.

Environmentally mediated changes in body size often underlie population responses to environmental change, yet this is not a universal phenomenon. Understanding when phenotypic change underlies population responses to environmental change is important for obtaining insights and robust predictions of population dynamics in a changing world. We develop a dynamic integral projection model that mechanistically links environmental conditions to demographic rates and phenotypic traits (body size) via changes in resource availability and individual energetics. We apply the model to the northern Yellowstone elk population and explore population responses to changing patterns of seasonality, incorporating the interdependence of growth, demography, and density-dependent processes operating through population feedback on available resources. We found that small changes in body size distributions can have large impacts on population dynamics but need not cause population responses to environmental change. Environmental changes that altered demographic rates directly, via increasing or decreasing resource availability, led to large population impacts in the absence of substantial changes to body size distributions. In contrast, environmentally driven shifts in body size distributions could occur with little consequence for population dynamics when the effect of environmental change on resource availability was small and seasonally restricted and when strong density-dependent processes counteracted expected population responses. These findings highlight that a robust understanding of how associations between body size and demography influence population responses to environmental change will require knowledge of the shape of the relationship between phenotypic distributions and vital rates, the population status with regard to its carrying capacity, and importantly the nature of the environmentally driven change in body size and carrying capacity.

Reintroduced wolves and hunting limit the abundance of a subordinate apex predator in a multi-use landscape.

Top-down effects of apex predators are modulated by human impacts on community composition and species abundances. Consequently, research supporting top-down effects of apex predators occurs almost entirely within protected areas rather than the multi-use landscapes dominating modern ecosystems. Here, we developed an integrated population model to disentangle the concurrent contributions of a reintroduced apex predator, the grey wolf, human hunting and prey abundances on vital rates and abundance of a subordinate apex predator, the puma. Increasing wolf numbers had strong negative effects on puma fecundity, and subadult and adult survival. Puma survival was also influenced by density dependence. Overall, puma dynamics in our multi-use landscape were more strongly influenced by top-down forces exhibited by a reintroduced apex predator, than by human hunting or bottom-up forces (prey abundance) subsidized by humans. Quantitatively, the average annual impact of human hunting on equilibrium puma abundance was equivalent to the effects of 20 wolves. Historically, wolves may have limited pumas across North America and dictated puma scarcity in systems lacking sufficient refugia to mitigate the effects of competition.

Can wildland fire management alter 21st-century subalpine fire and forests in Grand Teton National Park, Wyoming, USA?

In subalpine forests of the western United States that historically experienced infrequent, high-severity fire, whether fire management can shape 21st-century fire regimes and forest dynamics to meet natural resource objectives is not known. Managed wildfire use (i.e., allowing lightning-ignited fires to burn when risk is low instead of suppressing them) is one approach for maintaining natural fire regimes and fostering mosaics of forest structure, stand age, and tree-species composition, while protecting people and property. However, little guidance exists for where and when this strategy may be effective with climate change. We simulated most of the contiguous forest in Grand Teton National Park, Wyoming, USA to ask: (1) how would subalpine fires and forest structure be different if fires had not been suppressed during the last three decades? And (2) what is the relative influence of climate change vs. fire management strategy on future fire and forests? We contrasted fire and forests from 1989 to 2098 under two fire management scenarios (managed wildfire use and fire suppression), two general circulation models (CNRM-CM5 and GFDL-ESM2M), and two representative concentration pathways (8.5 and 4.5). We found little difference between management scenarios in the number, size, or severity of fires during the last three decades. With 21st-century warming, fire activity increased rapidly, particularly after 2050, and followed nearly identical trajectories in both management scenarios. Area burned per year between 2018 and 2099 was 1,700% greater than in the last three decades (1989-2017). Large areas of forest were abruptly lost; only 65% of the original 40,178 ha of forest remained by 2098. However, forests stayed connected and fuels were abundant enough to support profound increases in burning through this century. Our results indicate that strategies emphasizing managed wildfire use, rather than suppression, will not alter climate-induced changes to fire and forests in subalpine landscapes of western North America. This suggests that managers may continue to have flexibility to strategically suppress subalpine fires without concern for long-term consequences, in distinct contrast with dry conifer forests of the Rocky Mountains and mixed conifer forest of California where maintaining low fuel loads is essential for sustaining frequent, low-severity surface fire regimes.

Chronic wasting disease undermines efforts to control the spread of brucellosis in the Greater Yellowstone Ecosystem.

Wildlife diseases pose a substantial threat to the provisioning of ecosystem services. We use a novel modeling approach to study the potential loss of these services through the imminent introduction of chronic wasting disease (CWD) to elk populations in the Greater Yellowstone Ecosystem (GYE). A specific concern is that concentrating elk at feedgrounds may exacerbate the spread of CWD, whereas eliminating feedgrounds may increase the number of elk on private ranchlands and the transmission of a second disease, brucellosis, from elk to cattle. To evaluate the consequences of management strategies given the threat of two concurrent wildlife diseases, we develop a spatiotemporal bioeconomic model. GPS data from elk and landscape attributes are used to predict migratory behavior and population densities with and without supplementary feeding. We use a 4,800 km2 area around Pinedale, Wyoming containing four existing feedgrounds as a case study. For this area, we simulate welfare estimates under a variety of management strategies. Our results indicate that continuing to feed elk could result in substantial welfare losses for the case-study region. Therefore, to maximize the present value of economic net benefits generated by the local elk population upon CWD's arrival in the region, wildlife managers may wish to consider discontinuing elk feedgrounds while simultaneously developing new methods to mitigate the financial impact to ranchers of possible brucellosis transmission to livestock. More generally, our methods can be used to weigh the costs and benefits of human-wildlife interactions in the presence of multiple disease risks.

Individual variation creates diverse migratory portfolios in native populations of a mountain ungulate.

Ecological theory and empirical studies have demonstrated population-level demographic benefits resulting from a diversity of migratory behaviors with important implications for ecology, conservation, and evolution of migratory organisms. Nevertheless, evaluation of migratory portfolios (i.e., the variation in migratory behaviors across space and time among individuals within populations) has received relatively little attention in migratory ungulates, where research has focused largely on the dichotomous behaviors (e.g., resident and migrant) of partially migratory populations. Using GPS data from 361 female bighorn sheep (Ovis canadensis) across 17 (4 restored, 6 augmented, 7 native) populations in Montana and Wyoming, USA, we (1) characterized migratory portfolios based on behavioral and spatial migratory characteristics and (2) evaluated the relative influence of landscape attributes and management histories on migratory diversity. Native populations, which had been extant on the landscape for many generations, had more diverse migratory portfolios, higher behavioral switching rates, reduced seasonal range fidelity, and broad dispersion of individuals across summer and winter ranges. In contrast, restored populations with an abbreviated history on the landscape were largely non-migratory with a narrow portfolio of migratory behaviors, less behavioral switching, higher fidelity to seasonal ranges, and less dispersion on summer and winter ranges. Augmented populations were more variable and contained characteristics of both native and restored populations. Differences in migratory diversity among populations were associated with management histories (e.g., restored, augmented, or native). Landscape characteristics such as the duration and regularity of green-up, human landscape alterations, topography, and snow gradients were not strongly associated with migratory diversity. We suggest a two-pronged approach to restoring migratory portfolios in ungulates that first develops behavior-specific habitat models and then places individuals with known migratory behaviors into unoccupied areas in an effort to bolster migratory portfolios in restored populations, potentially with synergistic benefits associated with variation among individuals and resulting portfolio effects. Management efforts to restore diverse migratory portfolios may increase the abundance, resilience, and long-term viability of ungulate populations.

Weak spatiotemporal response of prey to predation risk in a freely interacting system.

The extent to which prey space use actively minimizes predation risk continues to ignite controversy. Methodological reasons that have hindered consensus include inconsistent measurements of predation risk, biased spatiotemporal scales at which responses are measured and lack of robust null expectations. We addressed all three challenges in a comprehensive analysis of the spatiotemporal responses of adult female elk (Cervus elaphus) to the risk of predation by wolves (Canis lupus) during winter in northern Yellowstone, USA. We quantified spatial overlap between the winter home ranges of GPS-collared elk and three measures of predation risk: the intensity of wolf space use, the distribution of wolf-killed elk and vegetation openness. We also assessed whether elk varied their use of areas characterized by more or less predation risk across hours of the day, and estimated encounter rates between simultaneous elk and wolf pack trajectories. We determined whether observed values were significantly lower than expected if elk movements were random with reference to predation risk using a null model approach. Although a small proportion of elk did show a tendency to minimize use of open vegetation at specific times of the day, overall we highlight a notable absence of spatiotemporal response by female elk to the risk of predation posed by wolves in northern Yellowstone. Our results suggest that predator-prey interactions may not always result in strong spatiotemporal patterns of avoidance.

Plasticity in elk migration timing is a response to changing environmental conditions.

Migration is an effective behavioral strategy for prolonging access to seasonal resources and may be a resilient strategy for ungulates experiencing changing climatic conditions. In the Greater Yellowstone Ecosystem (GYE), elk are the primary ungulate, with approximately 20,000 individuals migrating to exploit seasonal gradients in forage while also avoiding energetically costly snow conditions. How climate-induced changes in plant phenology and snow accumulation are influencing elk migration timing is unknown. We present the most complete record of elk migration across the GYE, spanning 9 herds and 414 individuals from 2001 to 2017, to evaluate the drivers of migration timing and test for temporal shifts. The timing of elk departure from winter range involved a trade-off between current and anticipated forage conditions, while snow melt governed summer range arrival date. Timing of elk departure from summer range and arrival on winter range were both influenced by snow accumulation and exposure to hunting. At the GYE scale, spring and fall migration timing changed through time, most notably with winter range arrival dates becoming almost 50 days later since 2001. Predicted herd-level changes in migration timing largely agreed with observed GYE-wide changes-except for predicted winter range arrival dates which did not reflect the magnitude of change detected in the elk telemetry data. Snow melt, snow accumulation, and spring green-up dates all changed through time, with different herds experiencing different rates and directions of change. We conclude that elk migration is plastic, is a direct response to environmental cues, and that these environmental cues are not changing in a consistent manner across the GYE. The impacts of changing elk migration timing on predator-prey dynamics, carnivore-livestock conflict, disease ecology, and harvest management across the GYE are likely to be significant and complex.