Recovery Strategy for the Woodland Caribou, Southern Mountain population (Rangifer tarandus caribou) in Canada - 2014 [Final]
- Executive Summary
- Recovery Feasibility Summary
- 1. COSEWIC Species Assessment Information
- 2. Species Status Information
- 3. Species Information
- 4. Threats
- 5. Population and Distribution Objectives
- 6. Broad Strategies and General Approaches to Meet Objectives
- 7. Critical Habitat
- 8. Measuring Progress
- 9. Statement On Action Plans
- 10. Glossary
- Appendix A: Effects on the Environment and Other Species
- Appendix B: Maps of Critical Habitat for Southern Mountain Caribou Local Population Units (LPUs)
- Appendix C: Biophysical Attributes for Southern Mountain Caribou Critical Habitat
3. Species Information
All caribou and reindeer in the world belong to one species, Rangifer tarandus. In Canada, caribou are found in all provinces and territories except for New Brunswick, Nova Scotia and Prince Edward Island (Figure 1). Four subspecies of caribou are currently recognized: Woodland Caribou (R.t. caribou); Peary Caribou (R. t. pearyi); Barren-ground Caribou (R. t. groenlandicus); and Grant’s Caribou (R. t. granti; Banfield 1961). Dawson’s Caribou (R. t. dawsoni) occurred on Haida Gwaii (i.e., Queen Charlotte Islands, BC) before their extinction in the early 1900s (Spalding 2000). Although Banfield’s (1961) subspecies classification is commonly used, a review and revision of the taxonomy of caribou is needed (COSEWIC 2011).
Description of Figure 1
Figure 1 is a map showing the range and status (COSEWIC) of different populations of caribou in Canada.
Based on the classification system used by COSEWIC in its 2002 assessment, Woodland Caribou are separated into six geographically distinct populations in Canada: Northern Mountain, Southern Mountain, Boreal, Forest-tundra, Atlantic-Gaspésie, and Newfoundland (COSEWIC 2002, Figure 2). This recovery strategy addresses the recovery of the southern mountain population of woodland caribou in Canada, which is located within the Southern Mountain National Ecological Area (SMNEA) in BC and Alberta (Thomas and Gray 2002).
Description of Figure 2
Figure 2 is a map of the National Ecological Areas established by COSEWIC in Canada. These are National Ecological Areas. Arctic, Atlantic, Boreal, Pacific, Prairie, Plains Great Lakes Northern Mountains, South Mountain.
Two "ecotypes” of caribou are recognized by the provinces within the southern mountain caribou population. These ecotypes broadly reflect adaptive behaviours of caribou (e.g., feeding, migration) to a variety of ecological conditions (e.g., amount and duration of snow cover, topography/terrain).
In BC, caribou that live in areas of relatively shallow snowpack and which feed primarily on terrestrial lichens (but also on arboreal lichens), are called ‘northern’ ecotype caribou, while caribou that live in deep snow areas and feed primarily on arboreal lichens are ‘mountain’ ecotype caribou (Stevenson and Hatler 1985, Heard and Vagt 1998). In Alberta, caribou that feed primarily on terrestrial lichens and spend at least part of their annual cycle in the mountains are similar to BC’s ‘northern’ ecotype but are called ‘mountain’ caribou (ASRD & ACA 2010).
In 2011, COSEWIC defined 12 Designatable Units (DUs) for caribou across Canada. DUs are discrete and evolutionarily significant units of caribou defined to address issues with the current taxonomy and with classification of ecotypes (COSEWIC 2011). That report splits southern mountain caribou into 3 DUs: Northern Mountain (DU7), Central Mountain (DU8), and Southern Mountain (DU9). The current southern mountain caribou population includes all of DU8 and DU9, but only the southern portion of DU7. The DU structure for caribou in western Canada is being reviewed as part of the update to the COSEWIC status report and subsequent reassessment in 2014.
In this recovery strategy, to retain the ecological and evolutionary distinction between the 3 DUs, southern mountain caribou in the Northern Mountain (DU7), Central Mountain (DU8) and Southern Mountain (DU9) DUs will be referred to as the Northern Group, Central Group and Southern Group, respectively (Table 2)
|Terrain/ Winter feeding strategy||Ecotype name||Location||Nationally Significant Population by National Ecological Area (SARA)||COSEWIC Designatable Unit|
|Southern mountain caribou Groupings|
|Shallow snow/ terrestrial lichen||BC: Northern||Northern BC||Northern Mountain||Northern Mountain||Not Applicable|
|BC: Northern||West central BC||Southern Mountain||Northern Mountain||Northern Group|
|BC: Northern||North central BC||Southern Mountain||Northern Mountain||Northern Group|
|Shallow snow/terrestrial lichen||BC: Northern||East central BC||Southern Mountain||Central Mountain||Central Group|
|Shallow snow/terrestrial lichen||Alberta: Mountain||West central Alberta||Southern Mountain||Central Mountain||Central Group|
|Deep snow/ arboreal lichen||BC: Mountain||Southeastern BC||Southern Mountain||Southern Mountain||Southern Group|
3.1 Species Description
Southern mountain caribou are a medium-sized (1.0-1.2 m shoulder height and weighing 110-210 kg) member of the deer family (Cervidae) (Thomas and Gray 2002). Adults have a dark brown coat with a creamy white neck, mane, shoulder stripe, underbelly, underside of the tail, and patch above each hoof (Banfield, 1974). Caribou have large, rounded hooves and large, widely spaced dew claws which help them walk on and dig through snow to gain access to lichens, their primary food during winter (Thomas and Gray 2002). Both male and female caribou have antlers during part of the year, a unique feature among the deer family (Thomas and Gray 2002). Antlers are erect and spreading with males having a flattened brow tine that points down over the forehead (BC Ministry of Environment, Lands and Parks 2000).
3.2 Population and Distribution
3.2.1 Local Population Units (LPUs) and Subpopulations
The southern mountain caribou population currently includes 38 recognized individual subpopulations. Four of those subpopulations have been extirpated (i.e.subpopulation reduced to zero caribou) since 2002. In this recovery strategy, the 38 subpopulations have been organized into "local population units” (LPUs). The LPUs take into account that the subpopulations were historically larger in size and have been fragmented into the currently recognized subpopulations. For subpopulations that are not grouped with others into a larger LPU, the LPU is equivalent to the subpopulation.
The geographic area that is occupied by a subpopulation is referred to in this strategy as the subpopulation's annual range. The annual range of an LPU consists of the combined annual ranges of all subpopulations within that LPU. Within the annual range, geographic areas occupied by caribou are further differentiated by season of use into seasonal ranges (e.g., winter range, summer range).
LPUs have been established and mapped using two different methods in this recovery strategy. For the Southern Group, the LPUs have been adopted from the Government of BC’s Mountain Caribou Recovery Implementation Plan, which refers to large, contiguous "Mountain Caribou Planning Units” rather than individual subpopulations. This results in the LPU often covering vast areas that are not currently occupied by a southern mountain caribou subpopulation. For the Northern and Central Groups, the LPUs have been established using the best available information and expertise about current and recently historic occupancy of geographic areas by southern mountain caribou subpopulations. This results in the LPU boundary largely equating to the boundary of the subpopulation(s) within it.
Annual LPU ranges, subpopulation boundaries, and seasonal ranges have been identified based on extensive studies of movements and seasonal range use of radio-collared caribou (e.g., Cichowski 1993, Terry and Wood 1999, Young and Roorda 1999, Poole et al.2000, Young et al. 2001, Roberts et al. 2003, Culling et al. 2005, Wittmer et al. 2005a, Jones 2007, ASRD & ACA 2010, van Oort et al. 2011, Williamson-Ehlers 2012, Seip and Jones 2013). Many of those radio-telemetry studies were conducted after the 1980s with some initiated as recently as 2002. For those subpopulations, annual ranges often reflect current distribution and habitat use, and may not adequately describe historically used areas and seasonal use patterns. The only subpopulation with limited information on habitat use and distribution is the Scott subpopulation.
3.2.2 Historical Distribution, Numbers and Trends
Historically, the distribution of southern mountain caribou in BC and Alberta was much larger and extended further south into the United States (Figure 3). In BC, a conservative estimate of the reduction of the extent of distribution for all caribou types since the arrival of Europeans is 20%, with the major change in distribution occurring in the southern portion of the province in the area occupied by southern mountain caribou (Spalding 2000). Hummel and Ray (2008) report that southern mountain caribou have been extirpated from approximately 40% of their historical extent of occurrence due to loss and change in habitats, primarily resulting from human activities. In Alberta, about 61% of the generalized maximum historical extent of occurrence of all caribou in the province is no longer occupied (Dzus 2001). Southern mountain caribou also occurred in most of the northwestern US states in the 19th century but are now extirpated (e.g. the last confirmed sighting of a caribou in Montana was in 1958), except for the South Selkirk subpopulation (US Fish and Wildlife Service 1993). However, the most recent survey of this subpopulation indicated that it is both small (estimate of 22 in 2014) and declining, raising concerns about the likelihood of the US portion of the annual range being occupied in the future (BC Ministry of Forests, Lands and Natural Resource Operations, unpublished data).
At the turn of the 20th century, the estimated number of caribou in all of BC was 30,000-40,000 (Spalding 2000). Aboriginal traditional knowledge holders stated that prior to the arrival of Europeans in north-eastern BC, caribou populations were so high that they were described to be "like bugs on the land” (Willson 2014). Historical records and more recent survey information suggest a general declining trend until about the 1940s, followed in some cases by an increase in numbers through to the 1960s, a subsequent decline in the late 1970s, an increase in the mid-late 1990s, and a decline to the present (Bergerud 1978, Stevenson & Hatler 1985, Seip & Cichowski 1996, Spalding 2000, Thomas & Gray 2002). These changes were more pronounced in the southern and central part of the province (i.e., within the boundaries of the southern mountain caribou population) than in the north. As a result of these changes, many Aboriginal groups have stopped hunting southern mountain caribou due to their concerns for the long-term survival of this species.
Limited historical population estimates are available for individual subpopulations in west-central Alberta, but Alberta Sustainable Resource Development & Alberta Conservation Association (2010, and references therein) cite "a significant decline in the number and size of caribou populations in Alberta”.
Changes in caribou numbers from the early 1900s until the 1970s have been attributed to changes in numbers and distribution of other prey, changes in numbers of predators, and overhunting. In southern and central BC, moose (Alces americanus) were largely absent or present at low densities until the late 1800s when they started becoming more common (Spalding 1990, Santomauro et al. 2012). The increase in moose provided predators with an alternate prey source. In the 1950s and 1960s, wide-scale predator poisoning programs targeting wolves (Canis lupus) and coyotes (Canis latrans) were conducted (Cringan 1957, Bergerud 1978, Edmonds 1988, Bergerud and Elliott 1998). Large legal harvests of caribou in the late 1960s and early 1970s in BC and Alberta (Bergerud 1978, Edmonds and Bloomfield 1984) combined with recovering wolf populations and adverse weather probably caused caribou population decreases in the 1970s.
Description of Figure 3
This figure is a map showing current distribution of the southern mountain caribou within the SMNEA (same as figure 1) in contrast with the approximate historic distribution.
3.2.3 Population numbers and trends
The 34 currently existing (extant) and 4 extirpated subpopulations of southern mountain caribou, comprising the 24 LPUs, are distributed across the southern two-thirds of BC and in the west-central portion of Alberta (Figure 4). One LPU’s annual range (South Selkirks) also extends partially into northern Idaho and Washington, USA.
Reliable current size and trend information is available for most southern mountain caribou subpopulations and LPUs. For some subpopulations, however, reliable surveys are difficult to conduct because a large number of the caribou are found below treeline during all seasons where they are harder to detect because of dense forest cover.
Based on the best available information, the current overall number of southern mountain caribou in Canada is estimated to be approximately 5,800 (Table 3). This is a total of all caribou in the LPUs, not only the mature individuals. Only the Itcha-Ilgachuz and Graham subpopulations are estimated to consist of 500 or more caribou. Over half (18 of 34) of the extant subpopulations consist of 50 or fewer caribou. All but two of the subpopulations with known long-term trends have declined, and four of those are currently extirpated. Of the 24 LPUs that are a combination of one or more subpopulations, ten have fewer than 100 caribou.
In the Northern Group, surveys for the Itcha-Ilgachuz and Telkwa subpopulations date back to the 1970s and 1960s respectively. Fewer estimates are available for the other subpopulations. However, population trend information is available for some subpopulations based on survey data, or on radio-collared caribou mortality rates and calf recruitment.
In the Central Group, surveys of the Kennedy Siding, Burnt Pine, Moberly, Quintette and the eastern portion of the Scott subpopulations are conducted during late winter when caribou are using high elevation alpine and subalpine habitat (Seip and Jones 2013). Surveys of the Tonquin, Brazeau and Maligne subpopulations are conducted in the fall when caribou are using high elevation alpine habitat. No reliable surveys have been conducted for the Narraway, Redrock-Prairie Creek and A La Peche subpopulations because many of the caribou in those subpopulations use low elevation forested habitat during winter, making them difficult to count. Population trends for subpopulations in the Central Group are based on mortality rates of radio-collared caribou and late winter calf recruitment counts. These have been tracked annually since at least 2002/03 for most subpopulations, and as far back as 1998/99 for the Redrock Prairie Creek and A La Peche subpopulations (ASRD & ACA 2010, Seip and Jones 2013, AESRD unpublished data).
In the Southern Group, population surveys are conducted during late winter when caribou are using high elevation subalpine habitat. Numerous surveys have been conducted for all subpopulations since the early 1990s
Description of Figure 4
Figure 4 is a map of the current distribution of sub-populations and local populations of mountain caribou in the South. Local populations of the northern group along the north and northwest boundaries of the National Ecological Area Southern Mountain (AENMS). Local populations of the Central group along the northeastern boundary of the AENMS. Local populations in the southern group are located in the interior and southern AENMS.
|#Table 3 notee||Prov||Local population unit (LPU)||Subpopulation||Population estimateTable 3 notef|
|Population TrendTable 3 noteg|
|1||BC||Chilcotin||Itcha-Ilgachuz||1685||2014||Decreasing||IncreasingTable 3 noteh|
|BC||Northern Group Total||3707||Unknown||Unknown|
|#||Prov||Local population unit (LPU)||Subpopulation||Population estimate|
|8||BC||Pine River||Scott||43||2014Table 3 notei||Unknown||Unknown|
|8||BC||Pine River||Kennedy Siding||30Table 3 notej||2014||Decreasing||Decreasing|
|8||BC||Pine River||Burnt Pine||0||2014||Extirpated||Decreasing|
|9||BC||Quintette||Quintette||106Table 3 notek||2014||Decreasing||Decreasing|
|10||BC / AB||Narraway||Narraway||96Table 3 notel||2012||Decreasing||Decreasing|
|11||AB||Redrock/Prairie Creek||Redrock/Prairie Creek||127Table 3 notel||2012||Decreasing||Decreasing|
|12||AB||A La Peche||A La Peche||88Table 3 notel||2012||Decreasing||Decreasing|
|13||AB||Jasper/Banff||BanffTable 3 notem||0||Extirpated|
|BC / AB||Central Group Total||563||Decreasing||Decreasing|
|#||Prov||Local population unit (LPU)||Subpopulation||Population estimate|
|14||BC||Hart Ranges||Hart Ranges||459||2013||Decreasing||Decreasing|
|15||BC||Upper Fraser||North Cariboo Mountains||222||2011||Decreasing||Decreasing|
|15||BC||Upper Fraser||George MountainTable 3 noten||0||Extirpated||Decreasing|
|15||BC||Upper Fraser||Narrow Lake||47||2014||Stable||Decreasing|
|16||BC||Mount Robson||Mount RobsonoTable 3 noteo||0||N/A||N/A|
|17||BC||Quesnel Highlands||Wells Gray (North)Table 3 notep||259||2013||Decreasing||Decreasing|
|18||BC||Wells Gray-Thompson||Wells Gray (South)Table 3 notep||133||2013||Decreasing||Decreasing|
|23||BC||Southwest Kootenay||South Selkirks||22||2014||Decreasing||Decreasing|
|24||BC||Southeast Kootenay||Purcells CentralTable 3 noteq||0||Extirpated||Decreasing|
|24||BC||Southeast Kootenay||Purcells South||19||2014||Stable||Decreasing|
|BC||Southern Group Total||1540||Decreasing||Decreasing|
3.3 Needs of the Southern Mountain Caribou
3.3.1 Habitat and biological needs
Southern mountain caribou require large ranges of relatively undisturbed, interconnected habitat where they can separate themselves (horizontally and by elevation) from predators; modify their geographic use in response to various natural and human-caused habitat disturbances and human activities; and access their preferred food sources.
Caribou select habitat at several scales and different subpopulations of southern mountain caribou differ in how they use their habitat. At the landscape scale, predator avoidance is the most important factor influencing selection (Johnson et al. 2002, Gustine et al. 2006a). In the Southern Group, caribou select high elevation habitats throughout most of the year, while predators and other prey are found primarily at low elevations; the greatest degree of overlap occurs during spring (Seip 1992a, Stotyn 2008, Steenweg 2011). Spatial separation from predators and other prey is especially critical during calving and early summer when calves are most vulnerable. During calving, caribou that disperse into high elevation alpine and subalpine habitat or to islands in lakes where predators are less abundant have higher newborn calf survival than caribou that calve below treeline (Bergerud et al. 1984, Bergerud 1985, Seip and Cichowski 1996). Females tend to return to the same location to calve each year.
During winter, southern mountain caribou require large patches of mature and old forests with abundant lichens. Old forest supports fewer primary prey species such as moose, elk (Cervus elaphus), and deer (Odocoileus sp.), so predator numbers (e.g., wolves, cougars [Puma concolor]) are also lower, resulting in fewer interactions with caribou during winter. Old and mature forests also have good sightlines because the trees are not as dense as in younger stands, making detection of predators easier. Also, lichens are more abundant in old and mature forests than in young forests. Subpopulations with high levels of recent habitat disturbance and very young forests and lower levels of old growth forest on their ranges have been shown to have lower survival rates (Wittmer et al. 2007).
In the Southern Group, the snowpack is deep and southern mountain caribou predominantly use high elevation mature and old subalpine forests in mid and late winter when the snowpack has hardened. This enables them to forage on arboreal lichens (primarily Bryoria spp.) that would otherwise be unreachable (Seip 1990, 1992a, Simpson et al. 1997, Hamilton et al. 2000, Terry et al. 2000, Apps et al. 2001). During early winter before snow has consolidated, they move to mid to low elevation mature and old forests (with some subpopulations moving as low as cedar/hemlock forests in valley bottoms) where they forage on arboreal lichens on fallen trees, lichen litterfall, and shrubs and forbs that remain accessible in snow wells (Seip 1992a, Mowat et al. 1998, Terry et al. 2000). Except for the South Selkirk and South Purcell subpopulations, caribou in the Southern Group also use lower elevation areas during spring, but return to higher elevations where they calve and spend the summer (Seip 1990, 1992a, Simpson et al. 1997, Hamilton et al. 2000).
Southern mountain caribou of the Central and Northern groups live in relatively shallow snow areas. They forage primarily on terrestrial lichens either in low elevation mature coniferous forests or on windswept alpine slopes during winter. In summer they are mostly at higher elevations in the mountains (Edmonds and Bloomfield 1984, Cichowski 1993, Brown et al. 1994, Terry and Wood 1999, Wood and Terry 1999, Young and Roorda 1999, Backmeyer 2000, Poole et al. 2000, Stronen 2000, Johnson et al. 2002, Szkorupa 2002, Culling et al. 2005, Jones 2007, Shepherd et al. 2007, Williamson-Ehlers 2012). During winter, these caribou primarily dig through the snow (crater) to access terrestrial lichens (Cladina spp. [preferred], Cladonia spp., Cetraria spp., and Stereocaulon spp.), but they also forage on arboreal lichens in low elevation forests, forested wetlands, and in subalpine habitats, especially during times when snow conditions are less favourable for cratering. Many subpopulations travel long distances between winter and summer ranges, while others winter and summer within the same general area. In Alberta, some caribou in the A La Peche and Redrock/Prairie Creek subpopulations no longer use the low elevation foothills portions of their annual ranges where habitat disturbance is high, and instead are living in the mountains year-round (Smith 2004). Currently, adult survival is higher for caribou that live year-round in the mountains than it is for those that migrate to low elevation ranges in the foothills (Hebblewhite et al. 2010a), but the subpopulations are still declining (Alberta Environment and Sustainable Resource Development, unpublished data). During spring migration, caribou generally use low elevation snow-free or low snow areas (Steventon 1996).
During spring and summer, southern mountain caribou are found mostly at high elevations although portions of some subpopulations also use low elevation habitat. In spring and summer, southern mountain caribou eat a wide variety of forbs, grasses, lichens, fungi, and the leaves of some shrubs (Simpson 1987, Seip 1990, Cichowski 1993, Thomas et al.1996).
In addition to seasonal ranges within their annual range, southern mountain caribou also require matrix range. Two types of matrix range are described in this recovery strategy. Type 1 matrix range consists of areas within an LPU’s annual range that have not been delineated as summer (e.g.spring, calving, summer, fall/rut) or winter range. Type 1 matrix may include seasonal migration areas (or portions of migration areas) and areas of lower use compared to delineated seasonal ranges. Type 2 matrix range consists of areas surrounding annual ranges where predator/prey dynamics influence predation within the subpopulation's annual range. Type 2 matrix range may also include areas of trace occurrences of caribou, dispersal zones between subpopulations, dispersal zones between LPUs.
The function of Type 1 matrix range is to provide some forage, connectivity between seasonal ranges, security from human disturbance, and a low risk of predation. The reason for identifying Type 1 matrix range is that habitat connectivity within an annual range allows for seasonal movement among habitats that have the different resources needed to satisfy life history requirements. This allows caribou to respond to habitat disturbance or habitat recovery (Saher and Schmiegelow 2005). Connectivity within annual ranges also allows for movement in response to changing environmental conditions (e.g. climate change).
Type 2 matrix range influences predator/prey dynamics within southern mountain caribou annual ranges and provides connectivity between subpopulations within and among LPUs. Recovery of southern mountain caribou requires that Type 2 matrix range be recognized and managed to maintain a low predation risk. Although caribou primarily use high elevation areas and/or habitat types where they are spatially separated from other prey and predators (Seip 1992a, Stotyn 2008, Hebblewhite et al.2010a, Steenweg 2011, Robinson et al. 2012, Williamson-Ehlers 2012), the habitat/prey/predator dynamics at lower elevations, and in areas adjacent to annual ranges, contribute to prey/predator dynamics and mortality on caribou within their annual ranges. This is because predators move beyond valley bottoms and also use higher elevations, especially during summer and fall (Whittington et al.2011). At the broad scale, wolf predation on caribou in the Southern Group occurs primarily at low elevations (Apps et al.2013).
In addition, Type 2 matrix range provides connectivity between subpopulations within and among LPUs and thereby allows for immigration and emigration, which helps to maintain genetic diversity and the species’ consequent resilience to environmental stressors (e.g., disease, severe weather). Weckworth et al. (2012) have demonstrated that isolation of subpopulations as a result of disturbance to the landscape (i.e., any form of human-caused or natural habitat alteration) can result in a significant reduction in genetic diversity. In addition, connectivity among annual ranges maintains the possibility of ‘rescue effects’, thereby facilitating recovery.
Table 4 summarizes features of southern mountain caribou seasonal and matrix range.
|Range||Southern GroupTable 4 noter||Central GroupTable 4 notes||Northern GrouptTable 4 notes|
|High elevation summer (e.g.spring, calving, summer, fall/rut) range|
|Low elevation summer (e.g.spring, calving, summer, fall/rut) range|
|High elevation winter range|
|Low elevation winter range|
|Matrix range (Type 1)|
|Matrix range (Type 2)|
3.3.2 Limiting factors
The reproductive output of woodland caribou is low relative to other ungulates, so it takes longer for their populations to increase than for other ungulates, making them more vulnerable to higher rates of mortality. Females typically do not produce young until three years of age and then have only one calf per year (Bergerud 2000). In addition, while all age classes of southern mountain caribou are vulnerable to predation, calf mortality can be especially high, particularly within the first 30 days after birth (Bergerud and Elliot 1986; Gustine et al. 2006b). In most cases predation is the main proximate causeFootnote 1 limiting southern mountain caribou population growth, since the survival of calves to one year of age is usually low and is often insufficient to compensate for annual adult mortality in declining populations (Edmonds and Smith 1991, Seip 1992b, Wittmer et al.2005b).
Small subpopulations with few adult females (and hence few births) and low calf survival have a low potential for population growth (Bergerud 1980; Bergerud 2000). In addition to being affected by reproductive and mortality rates related to their age distribution, small subpopulations can be disproportionately affected by random events such as avalanches, fire, and disease (e.g., the last 5 caribou in the Banff subpopulation died in an avalanche in 2009). Consequently, population growth is likely to be highly variable in small subpopulations, with an increased probability of extirpation (Caughley 1994).
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