Science to inform policy: Linking population dynamics to habitat for a threatened species in Canada

Quantifying forest disturbance regimes within caribou (Rangifer tarandus) range in British Columbia

Habitat disturbance is a major driver of the decline of woodland caribou (Rangifer tarandus caribou) in Canada. Different disturbance agents and regimes negatively impact caribou populations to different degrees. It is therefore critical that land managers and scientists studying caribou have a detailed understanding of the disturbance regimes affecting caribou habitat. In this work we use recent advances in satellite-based disturbance detection to quantify polygonal forest disturbance regimes affecting caribou ecotypes and herds in British Columbia (BC) from 1985 to 2019. Additionally, we utilize this data to investigate harvesting rates since the implementation of the Species at Risk Act (SARA) and publication of recovery strategies for caribou in BC. Southern Mountain caribou herds are the most threatened yet experienced the highest rates of disturbance, with 22.75% of forested habitat within their ranges disturbed during the study period. Over the study period, we found that in total, 16.4% of forested area was disturbed across all caribou herd ranges. Our findings indicate that caribou in BC face high, and in many cases increasing, levels of habitat disturbance. Our results provide a detailed understanding of the polygonal disturbance regimes affecting caribou in BC at the herd scale, and highlight the need for effective implementation of policies aimed at preserving caribou habitat.

Climate-informed forecasts reveal dramatic local habitat shifts and population uncertainty for northern boreal caribou

Most research on boreal populations of woodland caribou (Rangifer tarandus caribou) has been conducted in areas of high anthropogenic disturbance. However, a large portion of the species' range overlaps relatively pristine areas primarily affected by natural disturbances, such as wildfire. Climate-driven habitat change is a key concern for the conservation of boreal-dependent species, where management decisions have yet to consider knowledge from multiple ecological domains integrated into a cohesive and spatially explicit forecast of species-specific habitat and demography. We used a novel ecological forecasting framework to provide climate-sensitive projections of habitat and demography for five boreal caribou monitoring areas within the Northwest Territories (NWT), Canada, over 90 years. Importantly, we quantify uncertainty around forecasted mean values. Our results suggest habitat suitability may increase in central and southwest regions of the NWT's Taiga Plains ecozone but decrease in southern and northwestern regions driven by conversion of coniferous to deciduous forests. We do not project that boreal caribou population growth rates will change despite forecasted changes to habitat suitability. Our results emphasize the importance of efforts to protect and restore northern boreal caribou habitat despite climate uncertainty while highlighting expected spatial variations that are important considerations for local people who rely on them. An ability to reproduce previous work, and critical thought when incorporating sources of uncertainty, will be important to refine forecasts, derive management decisions, and improve conservation efficacy for northern species at risk.

Evaluating the impact of caribou habitat restoration on predator and prey movement

Fragmentation of the boreal forest by linear features, including seismic lines, has destabilized predator-prey dynamics, resulting in the decline of woodland caribou (Rangifer tarandus caribou) populations. Restoration of human-altered habitat has therefore been identified as a critical management tool for achieving self-sustaining woodland caribou populations. However, only recently has testing of the response of caribou and other wildlife to restoration activities been conducted. Early work has centered around assessing changes in wildlife use of restored seismic lines. We evaluated whether restoration reduces the movement rates of predators and their associated prey, which is expected to decrease predator hunting efficiency and ultimately reduce caribou mortality. We developed a new method for using cameras to measure fine-scale movement by measuring speed as animals traveled between cameras in an array. We used our method to quantify speed of caribou, moose (Alces alces), bears (Ursus americanus), and wolves (Canis lupus) on treated (restored) and untreated seismic lines. Restoration treatments reduced travel speeds along seismic lines of wolves by 1.38 km/h, bears by 0.55 km/h, and caribou by 1.57 km/h, but did not reduce moose travel speeds. Reduced predator and caribou speeds on treated seismic lines are predicted to decrease encounter rates between predators and caribou and thus lower caribou kill rates. However, further work is needed to determine whether reduced movement rates result in reduced encounter rates with prey, and ultimately reduced caribou mortality.

Lowering the rate of timber harvesting to mitigate impacts of climate change on boreal caribou habitat quality in eastern Canada

Many boreal populations of woodland caribou (Rangifer tarandus caribou) have declined in Canada, a trend essentially driven by the increasing footprint of anthropogenic disturbances and the resulting habitat-mediated apparent competition that increases predation pressure. However, the influence of climate change on these ecological processes remains poorly understood. We evaluated how climate change will affect boreal caribou habitat over the 2030-2100 horizon and in a 9.94 Mha study area, using a climate-sensitive simulation ensemble that integrates climate-induced changes in stand dynamics, fire regime, and different levels of commercial timber harvesting. We assessed the relative importance of these three drivers under projections made using different radiative forcing scenarios (RCP 2.6, 4.5, 8.5). Habitat quality was estimated from resource selection functions built with telemetry data collected from 121 caribou between 2004 and 2011 in 7 local populations. At the beginning of our simulations, caribou habitat was already structured along a south-to-north increasing quality gradient. Simulations revealed changes in forest cover that are driven by climate-induced variations in fire regime and scenarios of harvesting levels, resulting in the loss of older coniferous forests and an increase in deciduous stands. These changes induced a generalized decrease in the average habitat quality and in the percentage of high-quality habitat for caribou, and in a northward recession of suitable habitat. Timber harvesting was the most important agent of change for the 2030-2050 horizon, although it was slowly replaced by changes in fire regime until 2100. Our results clearly showed that it is possible to maintain the current average habitat quality for caribou in future scenarios that consider a reduction in harvested volumes, the only lever under our control. This suggests that we still have the capacity to conciliate socioeconomic development and caribou conservation imperatives in the face of climate change, an important issue debated throughout the species distribution range.

Multi-objective optimization can balance trade-offs among boreal caribou, biodiversity, and climate change objectives when conservation hotspots do not overlap

The biodiversity and climate change crises have led countries-including Canada-to commit to protect more land and inland waters and to stabilize greenhouse gas concentrations. Canada is also obligated to recover populations of at-risk species, including boreal caribou. Canada has the opportunity to expand its protected areas network to protect hotspots of high value for biodiversity and climate mitigation. However, co-occurrence of hotspots is rare. Here we ask: is it possible to expand the network to simultaneously protect areas important for boreal caribou, other species at risk, climate refugia, and carbon stores? We used linear programming to prioritize areas for protection based on these conservation objectives, and assessed how prioritization for multiple, competing objectives affected the outcome for each individual objective. Our multi-objective approach produced reasonably strong representation of value across objectives. Although trade-offs were required, the multi-objective outcome was almost always better than when we ignored one objective to maximize value for another, highlighting the risk of assuming that a plan based on one objective will also result in strong outcomes for others. Multi-objective optimization approaches could be used to plan for protected areas networks that address biodiversity and climate change objectives, even when hotspots do not co-occur.

Demographic responses of nearly extirpated endangered mountain caribou to recovery actions in Central British Columbia

Recovering endangered species is a difficult and often controversial task that challenges status quo land uses. Southern Mountain caribou are a threatened ecotype of caribou that historically ranged in southwestern Canada and northwestern USA and epitomize the tension between resource extraction, biodiversity conservation, and Indigenous Peoples' treaty rights. Human-induced habitat alteration is considered the ultimate cause of caribou population declines, whereby an increased abundance of primary prey-such as moose and deer-elevates predator populations and creates unsustainable caribou mortality. Here we focus on the Klinse-Za and Quintette subpopulations, part of the endangered Central Group of Southern Mountain caribou in British Columbia. These subpopulations were trending toward immediate extirpation until a collaborative group initiated recovery by implementing two short-term recovery actions. We test the effectiveness of these recovery actions-maternity penning of adult females and their calves, and the reduction of a primary predator, wolves-in increasing vital rates and population growth. Klinse-Za received both recovery actions, whereas Quintette only received wolf reductions, providing an opportunity to test efficacy between recovery actions. Between 1995 and 2021, we followed 162 collared female caribou for 414 animal-years to estimate survival and used aerial counts to estimate population abundance and calf recruitment. We combined these data in an integrated population model to estimate female population growth, total population abundance, and recovery action effectiveness. Results suggest that the subpopulations were declining rapidly (λ = 0.90-0.93) before interventions and would have been functionally extirpated (<10 animals) within 10-15 years. Wolf reduction increased population growth rates by ~0.12 for each subpopulation. Wolf reduction halted the decline of Quintette caribou and allowed them to increase (λ = 1.05), but alone would have only stabilized the Klinse-Za (λ = 1.02). However, maternity penning in the Klinse-Za increased population growth by a further ~0.06, which when combined with wolf reductions, allowed populations to grow (λ = 1.08). Taken together, the recovery actions in these subpopulations increased adult female survival, calf recruitment, and overall population growth, more than doubling abundance. Our results suggest that maternity penning and wolf reductions can be effective at increasing caribou numbers in the short term, while long-term commitments to habitat protection and restoration are made.

Behavioral "bycatch" from camera trap surveys yields insights on prey responses to human-mediated predation risk

Human disturbance directly affects animal populations and communities, but indirect effects of disturbance on species behaviors are less well understood. For instance, disturbance may alter predator activity and cause knock‐on effects to predator‐sensitive foraging in prey. Camera traps provide an emerging opportunity to investigate such disturbance‐mediated impacts to animal behaviors across multiple scales. We used camera trap data to test predictions about predator‐sensitive behavior in three ungulate species (caribou Rangifer tarandus; white‐tailed deer, Odocoileus virginianus; moose, Alces alces) across two western boreal forest landscapes varying in disturbance. We quantified behavior as the number of camera trap photos per detection event and tested its relationship to inferred human‐mediated predation risk between a landscape with greater industrial disturbance and predator activity and a “control” landscape with lower human and predator activity. We also assessed the finer‐scale influence on behavior of variation in predation risk (relative to habitat variation) across camera sites within the more disturbed landscape. We predicted that animals in areas with greater predation risk (e.g., more wolf activity, less cover) would travel faster past cameras and generate fewer photos per detection event, while animals in areas with less predation risk would linger (rest, forage, investigate), generating more photos per event. Our predictions were supported at the landscape‐level, as caribou and moose had more photos per event in the control landscape where disturbance‐mediated predation risk was lower. At a finer‐scale within the disturbed landscape, no prey species showed a significant behavioral response to wolf activity, but the number of photos per event decreased for white‐tailed deer with increasing line of sight (m) along seismic lines (i.e., decreasing visual cover), consistent with a predator‐sensitive response. The presence of juveniles was associated with shorter behavioral events for caribou and moose, suggesting greater predator sensitivity for females with calves. Only moose demonstrated a positive behavioral association (i.e., longer events) with vegetation productivity (16‐day NDVI), suggesting that for other species bottom‐up influences of forage availability were generally weaker than top‐down influences from predation risk. Behavioral insights can be gleaned from camera trap surveys and provide complementary information about animal responses to predation risk, and thus about the indirect impacts of human disturbances on predator–prey interactions.

Indigenous-led conservation: Pathways to recovery for the nearly extirpated Klinse-Za mountain caribou

Indigenous Peoples around the northern hemisphere have long relied on caribou for subsistence and for ceremonial and community purposes. Unfortunately, despite recovery efforts by federal and provincial agencies, caribou are currently in decline in many areas across Canada. In response to recent and dramatic declines of mountain caribou populations within their traditional territory, West Moberly First Nations and Saulteau First Nations (collectively, the "Nations") came together to create a new vision for caribou recovery on the lands they have long stewarded and shared. The Nations focused on the Klinse-Za subpopulation, which had once encompassed so many caribou that West Moberly Elders remarked that they were "like bugs on the landscape." The Klinse-Za caribou declined from ~250 in the 1990s to only 38 in 2013, rendering Indigenous harvest of caribou nonviable and infringing on treaty rights to a subsistence livelihood. In collaboration with many groups and governments, this Indigenous-led conservation initiative paired short-term population recovery actions, predator reduction and maternal penning, with long-term habitat protection in an effort to create a self-sustaining caribou population. Here, we review these recovery actions and the promising evidence that the abundance of Klinse-Za caribou has more than doubled from 38 animals in 2013 to 101 in 2021, representing rapid population growth in response to recovery actions. With looming extirpation averted, the Nations focused efforts on securing a landmark conservation agreement in 2020 that protects caribou habitat over a 7986-km² area. The Agreement provides habitat protection for >85% of the Klinse-Za subpopulation (up from only 1.8% protected pre-conservation agreement) and affords moderate protection for neighboring caribou subpopulations (29%-47% of subpopulation areas, up from 0%-20%). This Indigenous-led conservation initiative has set both the Indigenous and Canadian governments on the path to recover the Klinse-Za subpopulation and reinstate a culturally meaningful caribou hunt. This effort highlights how Indigenous governance and leadership can be the catalyst needed to establish meaningful conservation actions, enhance endangered species recovery, and honor cultural connections to now imperiled wildlife.

Increasing fire frequency and severity will increase habitat loss for a boreal forest indicator species

Climate change will lead to more frequent and more severe fires in some areas of boreal forests, affecting the distribution and availability of late-successional forest communities. These forest communities help to protect globally significant carbon reserves beneath permafrost layers and provide habitat for many animal species, including forest-dwelling caribou. Many caribou populations are declining, yet the mechanisms by which changing fire regimes could affect caribou declines are poorly understood. We analyzed resource selection of 686 GPS-collared female caribou from three ecotypes and 15 populations in a ~600,000 km² region of northwest Canada and eastern Alaska. These populations span a wide gradient of fire frequency but experience low levels of human-caused habitat disturbance. We used a mixed-effects modeling framework to characterize caribou resource selection in response to burns at different seasons and spatiotemporal scales, and to test for functional responses in resource selection to burn availability. We also tested mechanisms driving observed selection patterns using burn severity and lichen cover data. Caribou avoided burns more strongly during winter relative to summer and at larger spatiotemporal scales relative to smaller scales. During the winter, caribou consistently avoided burns at both spatiotemporal scales as burn availability increased, indicating little evidence of a functional response. However, they decreased their avoidance of burns during summer as burn availability increased. Burn availability explained more variation in caribou selection for burns than ecotype. Within burns, caribou strongly avoided severely burned areas in winter, and this avoidance lasted nearly 30 years after a fire. Caribou within burns also selected higher cover of terrestrial lichen (an important caribou food source). We found a negative relationship between burn severity and lichen cover, confirming that caribou avoidance of burns was consistent with lower lichen abundance. Consistent winter avoidance of burns and severely burned areas suggests that caribou will experience increasing winter habitat loss as fire frequency and severity increase. Our results highlight the potential for climate-induced alteration of natural disturbance regimes to affect boreal biodiversity through habitat loss. We suggest that management strategies prioritizing protection of core winter range habitat with lower burn probabilities would provide important climate-change refugia for caribou.

Demographic responses of a threatened, low-density ungulate to annual variation in meteorological and phenological conditions

As global climate change progresses, wildlife management will benefit from knowledge of demographic responses to climatic variation, particularly for species already endangered by other stressors. In Canada, climate change is expected to increasingly impact populations of threatened woodland caribou (Rangifer tarandus caribou) and much focus has been placed on how a warming climate has potentially facilitated the northward expansion of apparent competitors and novel predators. Climate change, however, may also exert more direct effects on caribou populations that are not mediated by predation. These effects include meteorological changes that influence resource availability and energy expenditure. Research on other ungulates suggests that climatic variation may have minimal impact on low-density populations such as woodland caribou because per-capita resources may remain sufficient even in “bad” years. We evaluated this prediction using demographic data from 21 populations in western Canada that were monitored for various intervals between 1994 and 2015. We specifically assessed whether juvenile recruitment and adult female survival were correlated with annual variation in meteorological metrics and plant phenology. Against expectations, we found that both vital rates appeared to be influenced by annual climatic variation. Juvenile recruitment was primarily correlated with variation in phenological conditions in the year prior to birth. Adult female survival was more strongly correlated with meteorological conditions and declined during colder, more variable winters. These responses may be influenced by the life history of woodland caribou, which reside in low-productivity refugia where small climatic changes may result in changes to resources that are sufficient to elicit strong demographic effects. Across all models, explained variation in vital rates was low, suggesting that other factors had greater influence on caribou demography. Nonetheless, given the declining trajectories of many woodland caribou populations, our results highlight the increased relevance of recovery actions when adverse climatic conditions are likely to negatively affect caribou demography.

Spatial familial networks to infer demographic structure of wild populations

In social species, reproductive success and rates of dispersal vary among individuals resulting in spatially structured populations. Network analyses of familial relationships may provide insights on how these parameters influence population-level demographic patterns. These methods, however, have rarely been applied to genetically derived pedigree data from wild populations.Here, we use parent-offspring relationships to construct familial networks from polygamous boreal woodland caribou (Rangifer tarandus caribou) in Saskatchewan, Canada, to inform recovery efforts. We collected samples from 933 individuals at 15 variable microsatellite loci along with caribou-specific primers for sex identification. Using network measures, we assess the contribution of individual caribou to the population with several centrality measures and then determine which measures are best suited to inform on the population demographic structure. We investigate the centrality of individuals from eighteen different local areas, along with the entire population.We found substantial differences in centrality of individuals in different local areas, that in turn contributed differently to the full network, highlighting the importance of analyzing networks at different scales. The full network revealed that boreal caribou in Saskatchewan form a complex, interconnected familial network, as the removal of edges with high betweenness did not result in distinct subgroups. Alpha, betweenness, and eccentricity centrality were the most informative measures to characterize the population demographic structure and for spatially identifying areas of highest fitness levels and family cohesion across the range. We found varied levels of dispersal, fitness, and cohesion in family groups. Synthesis and applications: Our results demonstrate the value of different network measures in assessing genetically derived familial networks. The spatial application of the familial networks identified individuals presenting different fitness levels, short- and long-distance dispersing ability across the range in support of population monitoring and recovery efforts.

Trophic consequences of terrestrial eutrophication for a threatened ungulate

Changes in primary productivity have the potential to substantially alter food webs, with positive outcomes for some species and negative outcomes for others. Understanding the environmental context and species traits that give rise to these divergent outcomes is a major challenge to the generality of both theoretical and applied ecology. In aquatic systems, nutrient-mediated eutrophication has led to major declines in species diversity, motivating us to seek terrestrial analogues using a large-mammal system across 598 000 km2 of the Canadian boreal forest. These forests are undergoing some of the most rapid rates of land-use change on Earth and are home to declining caribou (Rangifer tarandus caribou) populations. Using satellite-derived estimates of primary productivity, coupled with estimates of moose (Alces alces) and wolf (Canis lupus) abundance, we used path analyses to discriminate among hypotheses explaining how habitat alteration can affect caribou population growth. Hypotheses included food limitation, resource dominance by moose over caribou, and apparent competition with predators shared between moose and caribou. Results support apparent competition and yield estimates of wolf densities (1.8 individuals 1000 km-2) above which caribou populations decline. Our multi-trophic analysis provides insight into the cascading effects of habitat alteration from forest cutting that destabilize terrestrial predator-prey dynamics. Finally, the path analysis highlights why conservation actions directed at the proximate cause of caribou decline have been more successful in the near term than those directed further along the trophic chain.

Comparison of pre-fire and post-fire space use reveals varied responses by woodland caribou (Rangifer tarandus caribou) in the Boreal Shield

By regulating successional dynamics in Canada’s boreal forest, fires can affect the distribution of the Threatened woodland caribou (Rangifer tarandus caribou (Gmelin, 1788)). Caribou tend to avoid areas burned within the last 40 years; however, few studies have compared pre-fire and post-fire caribou observations. In this study, we used caribou GPS locations from the Boreal Shield of Saskatchewan, Canada, to assess the short-term response of caribou to areas that burned while they were collared (hereafter recent burns). We used a “before–after, control–impact” design to compare the overlap of pre-fire and post-fire seasonal home ranges to the overlap of year-to-year seasonal home ranges. Caribou rarely encountered recent burns and when they did, they adjusted their space use in variable and complex ways that were largely indistinguishable from regular, interannual variation. Caribou tended to reduce use of recent burns in summer–autumn and winter, but not during the calving season, in some cases shifting their home range to incorporate more burned habitat. We conclude that recently burned areas (<5 years) may provide habitat value to woodland caribou, particularly during the calving season, requiring a more flexible approach to interpret fire in habitat management strategies.