Demographic responses of nearly extirpated endangered mountain caribou to recovery actions in Central British Columbia (original) (raw)
Related papers
Biodiversity and Conservation, 2020
Mountain caribou, a behaviourally and genetically distinct set of ecotypes of the Woodland caribou (Rangifer tarandus caribou) restricted to the mountains of western Canada, have undergone severe population declines in recent decades. Although a broad consensus exists that the ultimate driver of these declines has been the reduction of habitat upon which mountain caribou depend, research and policy attention has increasingly focused on pre-dation. Recently, Serrouya et al. (Proc Nat Acad Sci USA 116:6181-6186, 2019) analysed population dynamics data from 18 subpopulations in British Columbia and Alberta, Canada, subject to different treatments and 'controls', and concluded that lethal wolf control and maternal caribou penning provide the most effective ways to stabilize population declines. Here we show that this inference was based on an unbalanced analytical approach that omitted a null scenario, excluded potentially confounding variables and employed irreproducible habitat alteration metrics. Our reanalysis of available data shows that ecotype identity is a better predictor of population trends than any adaptive management treatments considered by Serrouya et al. Disparate behavioural characteristics and responses to industrial disturbance among ecotypes suggest it may be incorrect to assume that adaptive management strategies that might benefit one ecotype are transferable to another.
Biological Conservation, 2010
Population viability analyses (PVA) are frequently employed to develop recovery plans and inform management of endangered species. Translating results from PVA into meaningful management recommendations often depends on an understanding of how population parameters change with environmental conditions as well as population density. The decline of mountain caribou (Rangifer tarandus caribou) in British Columbia, Canada, is believed to be caused by apparent competition with alternative prey species following changes to the forest age structure from timber harvest and wildfire. In addition, populations have been shown to decline at faster rates at low population density. To evaluate the potential effects of habitat change and population density on population persistence, we used stochastic projection models for 10 distinct populations varying in initial size from <10 to approximately 150 females. In an initial model, we used estimates of vital rates based on information sampled from >350 radiocollared caribou between 1984 and 2004. We then compared the results of the initial model to a set of models that evaluated the effects of habitat conditions and population density via their expected relationships to female adult survival. Assuming that vital rates remain constant over a 200-year time frame, only three populations have high probabilities (>0.95) of extinction. When models incorporate the declines in adult female survival know to occur with increasing proportions of young forest and declining population densities, all 10 populations are predicted to decline to extinction within <200 years. Based on our results, we suggest that PVA models that fail to incorporate the effects of changes in vital rates with habitat and population density may lead to overly optimistic assessments of the probability of population persistence in endangered species.
How Best to Proceed with Western North American Woodland Caribou: Get Back to Basics? - JULY 2023
Maintaining an umbilical link between wildlife management and research is essential to ensure that applied research fills critical knowledge gaps to foster the development, advancement, testing and modification of socially acceptable and effective management actions. A detailed review of contemporary literature for threatened and endangered (Species at Risk Act, Environment Canada) boreal, mountain and northern woodland caribou (Rangifer tarandus caribou) in western North America, places them as victims of persistent, landscape scale, anthropogenic disturbances that tend to increase the extent of early successional forest areas favoured by moose (Alces alces), elk (Cervus canadensis), and/or deer (Odocoileus spp.) expensed against the mature forest communities and peatlands they have specialized to exploit for over a million years. The resulting range overlap of these caribou with their interspecific competitors, including their primary predators, wolves, (Canis lupus) and bears (Ursus spp.) has exposed adult and/or neonate caribou to higher rates of incidental depredation that has resulted in critical declines, and in some cases, extirpation of a number of caribou populations. This relationship is referred to as an example of the theory of Apparent Competition (AC), the existence of which has dominated the human approach to both research and the management treatment of woodland caribou across their range of distribution in Canada. The powerful and progressive emerging role and influence of GPS (Global Positioning Systems), GIS (Global Information Systems), neck-mounted video cameras, and SSAP (sophisticated statistical analysis package) technologies to effecting paradigm shifts in the ways in which scientists perceive nature cannot be overstated. Wolves, moose, elk, deer and caribou have proven to be excellent candidates for geospatial research given the relative speed to locate (aerial tracking), capture and place battery-powered GPS digital signal transmitter collars on animals during winter months where high resolution spatially referenced locational datasets can be downloaded in real time on demand. These data can then be analyzed to extract statistically important habitat relationships, and when combined with archived locational data, provide a compelling spatial-temporal story. The results of remote digital locational analysis efforts do not in themselves present documentary-level evidence of the predator/prey dynamic, but they do enhance insights into species’ seasonal habitat preferences including distance from features analyses. The recent application of neck-mounted video cameras placed on predators however, have been particularly revealing respecting the nature of the predator-prey dynamic. Radio-tagged subjects also provide researchers the timely opportunity to track mortalities and undertake forensic level investigations regarding causes of mortalities increasing the confidence of estimates of adult survival and recruitment. There has been however, an obvious tendency of field investigators to focus their data sampling efforts on caribou and their interspecific competitors (ICs) cohabiting ranges in western Canada and wolves regardless of the presence of other predators (brown bears, black bears, coyotes, wolverines, lynx, cougars, and/or eagles). This narrow focus essentially introduced a strong bias in which wolves, regardless of the degree of background effects (i.e., range disturbance, other predators), were broadly incriminated as the proximate direct cause of most caribou population failures. This manuscript tracks the emergence of such biases since the early 1970’s that continue to dominate management strategies to this day. The alternative would be the transparent pursuit of data, information and knowledge systems that would decrease the predictive uncertainty of management strategies and openly address the multi-predator/multi-prey dynamic that has evolved out of a broad range of anthropogenic landscape-level disturbances within which caribou struggle to find refuge and productivity. There also exists a strong tendency in recent years for ecologists to overlook the pervasive role of ‘bottom-up’ processes (i.e., variability in seasonal weather trends, patterns of plant phenology, and/or extreme ambient conditions), in shaping their perceptions of the relative well-being of each of the predator and prey at the local, range, and landscape levels, notwithstanding the inarguable mystery of the existence of synchronous temporal trends in population metrics observed across extremely broad bio-geoclimatic zones. This manuscript provides an attempt to explore a comprehensive review of the 50+ year investigative record for a threatened species in context of the diverse ecological, economic, political, social, cultural and academic interests that have forged a range of approaches to their management across Canada, while keeping in mind that wildlife are a public trust resource implying some role for the public in decision-making. Thus, while both federal, provincial and territorial governments are ultimately charged as the custodians of this public resource, their most important role should be to prepare and maintain fertile ground for meaningful public participation in the decision processes, and to incentivize the development and testing of novel solutions that meet the ethical standards of all participants. Adaptive Resource Management (ARM) approaches bolstered by applied research, logically offers the best paths forward but requires that government provide the leadership to reach out to the public. This document reviews and weighs the impacts of government decisions of the past, including evaluations of i) wolf culling ii) fertility control iii) diversionary and supplemental feeding iv) maternity enclosures v) inter-specific prey reductions vi) vegetation management vii) access reduction and, viii) wild to wild translocations.
Rangifer, 2003
Barren ground caribou (Rangifer tarandus) were reintroduced to the Nushagak Peninsula, Alaska in February of 1988 after an absence of more than 100 years. Since reintroduction, herd growth and population dynamics have been monitored closely. At this time, there has been no significant dispersal from the herds' core range. The Nushagak Peninsula Caribou Herd (NPCH) grew rapidly from 146 reintroduced individuals to over 1000 in 13 years. Dramatic mean annual growth during the first 6 years (1988)(1989)(1990)(1991)(1992)(1993)(1994) of 38% (r = 0.32) can be attributed to the high percentage of females in the initial reintroduction, high calf production and survival, exceptional range conditions, few predators, and no hunting. However, the populations' exceptional growth (peak counts of 1400) slowed and stabilized between 1996¬ 1998 and then decreased between 1998 and 2000. Size, body condition and weights of calves captured in 2000 were significantly lower than those captured in 1995 and 1997. Although calf production also decreased from close to 100% (1990-1995) to about 91% (1996-2000), overall calf survival continued to be high. Legal harvest began in 1995, and harvest reports have accounted for approximately 3% of population mortality annually. Although brown bears (Ursus arctos) and wolves (Canis lupus) are present, the extent of predation is unknown. Mean home range of the NPCH was 674 km 2 and group sizes were greatest during post-calving aggregation in July (x = 127). Caribou population density on the Nushagak Peninsula reached approximately 1.2 caribou/km 2 in 1997 before declining to about 1.0 caribou/km 2 . A range survey in 1994 noted only trace utilization of lichens on the Nushagak Peninsula by caribou. A subsequent survey in 1999 found moderate to severe utilization in 46% of plots, suggesting the reintroduced herd was beginning to alter range condition. Between 1997 and 2000, both calf production and condition of 10-month-old calves declined. Calving has also been delayed in recent years. However, we suspect the reduced herd growth can be attributed to increasing hunting pressure and some dispersal of caribou from the Peninsula, not reduced range condition.
Invading white-tailed deer change wolf-caribou dynamics in northeastern Alberta
The Journal of Wildlife Management, 2011
Human-caused habitat change has been implicated in current woodland caribou (Rangifer tarandus caribou) population declines across North America. Increased early seral habitat associated with industrial footprint can result in an increase in ungulate densities and subsequently those of their predator, wolves (Canis lupus). Higher wolf densities can result in increased encounters between wolves and caribou and consequently higher caribou mortality. We contrasted changes in moose (Alces alces) and deer (Odocoileus spp.) densities and assessed their effects on wolf-caribou dynamics in northeastern Alberta, Canada, pre (1994Canada, pre ( -1997Canada, pre ( ) versus post (2005Canada, pre ( -2009 major industrial expansion in the region. Observable white-tailed deer (O. virginianus) increased 17.5-fold but moose remained unchanged. Wolf numbers also increased from approximately 6-11.5/1,000 km 2 . Coincident with these changes, spatial overlap between wolf pack territories and caribou range was high relative to the mid-1990s. The high number of wolf locations in caribou range suggests that forays were not merely exploratory, but rather represented hunting forays and denning locations. Scat analysis indicated that wolf consumption of moose declined substantively during this time period, whereas use of deer increased markedly and deer replaced moose as the primary prey of wolves. Caribou increased 10-fold in the diet of wolves and caribou population trends in the region changed from stable to declining. Wolf use of beaver (Castor canadensis) increased since the mid-1990s. We suggest that recent declines in woodland caribou populations in the southerly extent of their range have occurred because high deer densities resulted in a numeric response by wolves and consequently higher incidental predation on caribou. Our results indicate that management actions to conserve caribou must now include deer in primary prey and wolf reduction programs. ß 2011 The Wildlife Society.
Effects of control on the dynamics of an adjacent protected wolf population in interior Alaska
Wildlife Monographs, 2017
Long-term wolf (Canis lupus) research programs have provided many insights into wolf population dynamics. Understanding the mechanisms controlling responses of wolf populations to changes in density, environmental conditions, and human-caused mortality are important as wolf management becomes increasingly intensive. Competition with humans for ungulate prey has led to large-scale wolf control programs, particularly in Alaska, and although wolf populations may sustain relatively high (e.g., 22-29%) rates of conventional harvest, control programs are specifically designed to have lasting population-level effects. Understanding the broader impacts of wolf control efforts on the surrounding area is of particular concern for conservation agencies such as the United States National Park Service, whose mandates generally preclude the artificial reduction of populations of native predators, particularly for the primary purpose of increasing available prey biomass for human harvest. Detailed assessments of the factors influencing population vital rates (i.e., survival, natality, dispersal) and population trajectory in the context of control efforts are critical for understanding complex ecological relationships between wolves and their prey and informing management of each. Using a long-term dataset and a powerful new integrated modeling approach, we assessed the effects of wolf control on the dynamics of a monitored wolf population residing primarily within an adjacent protected area where wolf control activities were prohibited. We monitored wolf population dynamics in Yukon-Charley Rivers National Preserve (YUCH) in interior Alaska, USA for 22 years (1993-2014). During our study, 2 large-scale wolf control programs were implemented in the surrounding area with the primary goal of increasing the size of the Fortymile caribou herd. We used known-fate data based on relocations of marked wolves and repeated counts of associated pack mates to estimate survival, dispersal, and natality rates. We jointly analyzed these data using an integrated modeling approach, thereby providing inference to the entire resident, pack-dwelling population of wolves using YUCH. Apparent survival (i.e., including mortalities and dispersals) was lower in the study area during the lethal control period, indicating a direct additive effect of control despite the prohibition of control efforts inside YUCH boundaries. Apparent survival was higher in years following winters with above-average snowfall, corresponding with a predicted increase in ungulate prey vulnerability the following year. Extraterritorial forays were associated with lower apparent survival rates, particularly after the initiation of lethal wolf control in the surrounding area. In general, mortalities tended to occur evenly throughout the year, whereas dispersal rates increased during late winter and early spring. Dispersals accounted for approximately half of the observed losses in our collared sample across all age classes (excluding known breeders), although yearlings were the most likely to disperse. Sustained reductions in wolf densities outside the YUCH boundary during both wolf control programs also allowed us to directly assess the effects of reduced density on vital rates. Natality rates (estimated number of individuals added to each pack over the May-Aug interval) increased sharply over the course of each control program, suggesting a strong reproductive response to large-scale reductions in wolf densities in the surrounding area. Natality rates dropped rapidly between the 2 control programs, further supporting this conclusion. Smaller pack sizes and losses of known breeders were associated with lower natality rates per pack in the following year, suggesting human-caused mortality could have direct short-term effects on productivity by reducing pack sizes and removing breeders. However, although control can reduce the fecundity of individual packs in the short term, adjacent populations quickly respond to reduced wolf density by increasing natality rates. Estimates of wolf density based on relocations of marked individuals within packs were dependent on sample size and could not be used to reliably estimate population growth rate (l). As an alternative, we developed a new metric, l à , which assessed whether natality was sufficient to offset population losses on an annual basis, under the assumption that the minimum functional unit in a wolf population is a breeding pair. When l à decreased below 1.0
The role of predation in the decline and extirpation of woodland caribou
Oecologia, 2005
To select appropriate recovery strategies for endangered populations, we must understand the dynamics of small populations and distinguish between the possible causes that drive such populations to low numbers. It has been suggested that the pattern of population decline may be inversely density-dependent with population growth rates decreasing as populations become very small; however, empirical evidence of such accelerated declines at low densities is rare. Here we analyzed the pattern of decline of a threatened population of woodland caribou (Rangifer tarandus caribou) in British Columbia, Canada. Using information on the instantaneous rate of increase relative to caribou density in suitable winter foraging habitat, as well as on pregnancy rates and on causes and temporal distribution of mortalities from a sample of 349 radiocollared animals from 15 subpopulations, we tested 3 hypothesized causes of decline: (a) food regulation caused by loss of suitable winter foraging habitat, (b) predation-sensitive foraging caused by loss of suitable winter foraging habitat and (c) predation with caribou being secondary prey. Population sizes of caribou subpopulations ranged from <5 to >500 individuals. Our results showed that the rates of increase of these subpopulations varied from À0.1871 to 0.0496 with smaller subpopulations declining faster than larger subpopulations. Rates of increase were positively related to the density of caribou in suitable winter foraging habitat. Pregnancy rates averaged 92.4% ±2.24 and did not differ among subpopulations. In addition, we found predation to be the primary cause of mortality in 11 of 13 subpopulations with known causes of mortality and predation predominantly occurred during summer. These results are consistent with predictions that caribou subpopulations are declining as a consequence of increased predation. Recovery of these woodland caribou will thus require a multispecies perspective and an appreciation for the influence of inverse density dependence on population trajectories.
Fall supplemental feeding increases population growth rate of an endangered caribou herd
PeerJ
Most woodland caribou (Rangifer tarandus caribou) populations are declining primarily because of unsustainable predation resulting from habitat-mediated apparent competition. Wolf (Canis lupus) reduction is an effective recovery option because it addresses the direct effect of predation. We considered the possibility that the indirect effects of predation might also affect caribou population dynamics by adversely affecting summer foraging behaviour. If spring and/or summer nutrition was inadequate, then supplemental feeding in fall might compensate for that limitation and contribute to population growth. Improved nutrition and therefore body condition going into winter could increase adult survival and lead to improved reproductive success the next spring. To test that hypothesis, we fed high-quality food pellets to free-ranging caribou in the Kennedy Siding caribou herd each fall for six years, starting in 2014, to see if population growth rate increased. Beginning in winter 2015–1...
ARCTIC, 1988
The George River caribou herd in northern QuebeclLabrador increased from about 5000 animals in 1954 to 472 200 (or 1.1 caribou.km.') prior to the 1984 calving season. The range used by the herd expanded from 160 O00 to 442 O00 km2 for the period 1971-84. The exponential rate of increase (r) was estimated at O. 11 in the 1970s. Calkfemale ratio in autumn was relatively constant (x = 0.52) from 1973 to 1983, but decreased to about 0.39 in 1984-86. The harvest rate was relatively low in the 1970s (about 3%.yr"), but seemingly increased in the mid-1980s to 5-7% as a result of more liberal regulations and a greater impetus to exploit caribou for subsistence. The cumulative impact of lower calf recruitment and more intensive hunting may have appreciably depressed the growth rate of the herd in 1984-86. A greater year-round competition for food resources and a greater energy expenditure associated with range expansion are presented as probable regulatory factors for the George River herd. It is argued that the nature of caribou-habitat interactions in continental regions generate long-term fluctuations in caribou numbers if human exploitation remains low. At present, wolf predation does not appear to be an important mortality factor capable of regulating the George River herd.