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Woodland Caribou (Rangifer Tarandus Caribou)

Update
COSEWIC Status Report
on the
Woodland Caribou
Rangifer tarandus caribou

Atlantic-Gaspésie Population
Boreal Population
Southern Mountain Population
Northern Mountain Population
Newfoundland Population

in Canada

Donal C. Thomas1
David R. Gray2

2002

Species Information

Name and Classification

Woodland caribou in Canada are classified as Rangifer tarandus (Lin.), subspecies caribou (Gmelin 1788, Banfield 1961, 1974). Definitions are absolutely essential when discussing species, subspecies, metapopulations, populations, subpopulations, local populations, herds, demes, clines, and intergrades. Lack of definitions in the literature has led to much confusion. Not only are definitions arbitrary and variable among authors but interpretation of them varies even more. The definition for species-at-risk includes “…species, subspecies, or biologically distinct population …” (COSEWIC 2000a, 2000c).

All caribou and reindeer in the world are one species and presumed able to interbreed and produce viable, fertile offspring. One definition of species is “groups of actually or potentially interbreeding populations that are reproductively isolated from other such groups” (Mayr 1942). One of several definitions of subspecies is a geographically defined aggregate of local populations, which differ taxonomically from other subdivisions of the species (Mayr 1969). The degree of difference necessary to delineate subspecies has confounded taxonomists. Avice and Ball (1990) suggested that evidence for subspecies should come from concordant distribution of multiple, independent, genetically based traits. O’Brien and Mayr (1991) suggested that subspecies shared a unique geographic range or habitat, a group of phylogenetically concordant phenotypic characters, and a unique natural history. Occasional interbreeding of overlapping (sympatric) distributions or introgression of members of one subspecies into another is consistent with the subspecies definition (O’Brien and Mayr 1991).

The term biologically distinct population is also arbitrary but provides some flexibility. We do not have sufficient information on the genetic status of many populations to ascertain if they are genetically distinct, however that is defined. On the other hand, all small local populations, which have been isolated for more than 100 years, are likely to be genetically distinct, based on analysis of microsatellite DNA (C. Strobeck pers. comm. 2000). There are no accepted criteria for what degree of genetic difference constitutes distinct populations. It is not currently possible to translate genetic differences to functional differences. The biological component of biologically distinct population allows us to use ecological similarities and differences, phenotype, and behavior to group and separate populations of caribou. Phenotype and behavior have genetic and environmental components, which are difficult to partition. More genetic and behavioral information is needed before there can be any consensus on what conservation units of caribou require special protection.

What is a population? A broad definition includes all individuals of a species in a defined geographic area. Such areas should be ecologically significant geographic areas or ecoareas/ecoregions and not political boundaries. Over time, a species may form different ecotypes in different environments such as ecozones, ecoregions, and ecodistricts. Banfield (1961) used the term geographic population and Kelsall (1984) followed that terminology. However, Banfield (1961) also referred to statistical populations for grouping measurements of skeletal parts. For clarity, “population” should always be specified with adjectives “biological,” “geographic,” “ecological,”  “local,” “COSEWIC,” “statistical,” “sub-,“ etc.

The term "population" is used variously for an ecotype, a phenotype, and caribou within a specified geographic area, management unit, or jurisdiction. In this report, the definition of population recommended in the 1994 Revised COSEWIC Population Guidelines is used, i.e., "A population is considered to be a group of individuals of a single biological species occupying a defined area."  The 2000 ((COSEWIC 2000c) definition is “a geographically or otherwise distinct group (a portion of a total population) of interbreeding individuals which has little interchange of individuals with other such groups…).” Compare that definition with one adopted by the International Union for the Conservation of Nature (IUCN) for a regional population at a global scale. "The portion of the global population within the area being studied" (IUCN 1994) and their definition of subpopulation as "geographically or otherwise distinct groups of the global population between which there is little interchange. "  Thus, at a global scale the (COSEWIC populations could be considered subpopulations of Rangifer tarandus instead of populations. This is a top down approach. With a bottom up approach, the geographically defined local population is the basic unit for conservation.

Demes are a level below species and may substitute for subspecies if the latter cannot be partitioned. A deme is a group of individuals more genetically similar to each other than to other individuals, usually with some degree of spatial isolation as well (Wells and Richmond 1995). Metapopulation is, perhaps, the next grouping using a broad definition, i.e., a population of populations with actual or potential immigration/emigration among them. Natural re-colonization is possible should a local population die out. Grouping should be based on geography, ecology, and caribou behaviour. Groupings of metapopulations should be consistent with populations recognized by COSEWIC. Metapopulations along with some isolated local populations constitute the distribution of woodland caribou in Canada. Not enough is known about movements among most geographic groups of caribou to confidently classify and map them into subpopulations, populations, and metapopulations. Furthermore, the status of groups is dynamic. Most collared caribou are adult females that are expected to have fidelity to range where they were born and lived for at least 2 or 3 years before being collared. Young males are more likely to emigrate to another local population. The term interchange should rarely be used for it refers to mutual exchange, whereas most movements will be immigrations or emigrations.

A local population (geographic population) is the basic unit of conservation. Some authors use the term subpopulation to refer to a component of a local population whose individuals remain separate from others for part of a year or for many years. Populations are identified geographically though their boundaries may change with time and for many reasons. In reality, researchers seldom know whether they are investigating a subpopulation, a local population, or a metapopulation. Such designations require long-term monitoring of male and female marked caribou of all ages. As with range boundaries, group designation may change with changes in population size, vegetation (e.g., fire, other disturbances, and range overutilization), weather, and human activities (hunting and developments).

The term herd refers to a group of caribou that occupies a specific range or geographic area and appears to be separate from other such groups (Banfield 1954). It had a centre of habitation (Skoog 1968) and traditional calving ground (Thomas 1969). Overlap of range in winter was observed and accepted. The degree of mixing with other herds generally was not known but a small degree of emigration or immigration was acceptable to the herd definition. The key point regarding genetic mixing is the location of caribou populations, subpopulations, and individuals during the breeding season in October. What was previously mapped as general extent of occurrence of caribou in the boreal forest (Fig. 4) now is being delineated to encompass isolated or semi-isolated herds (local populations) equivalent in most cases to areas of occupancy (Fig. 5).


Figure 4: Current (solid lines) and Southern Limit of Historical (dashed line) Extent of Occurrence of Forest-dwelling Woodland Caribou in North Americain 2001

Figure 4.  Current (solid lines) and southern limit of historical (dashed line) extent of occurrence of forest-dwelling woodland caribou in North Americain 2001. Historical data from Kelsall (1984) and Hatter (pers. comm. 2000).

Historical data from Kelsall (1984) and Hatter (pers. comm. 2000).


Figure 5: Area of Occupation (current ranges) of Local Populations of Forest-dwelling Woodland Caribou in North Americain 2000

Figure 5.  Area of occupation (current ranges) of local populations of forest-dwelling woodland caribou in North Americain 2000. Data from maps supplied by provincial and territorial jurisdictions in 2000 and 2001.

Data from maps supplied by provincial and territorial jurisdictions in 2000 and 2001.

In this report, we use local population and subpopulation rather than herd and subherd to conform to IUCN and (COSEWIC terminology and literature on other species. More or less distinct local populations within COSEWIC populations are subpopulations at a national scale. The term herd is synonymous with local population, subpopulation, and seasonal component such as winter distribution. Some local populations are migratory, some have seasonal shifts in distribution, and some move little. Consequently, no single term adequately describes them. Though termed forest-dwelling caribou, they may occupy alpine tundra and open peatlands during summer and even in winter.

The naming of populations of forest-dwelling woodland caribou after location of calving grounds is less common than for the forest–tundra ecotype. Often population names refer to locations of traditional winter ranges (Farnell et al. 1996, Kuzyk et al. 1999). Three “mountain” populations in Alberta have overlapping summer range but distinct breeding areas and are named after the location of current winter ranges (Edmonds 1988, Brown and Hobson 1998). However, suitable calving and summer habitat is the most critical component of the range of most local populations.

The concept of ecotypes has gained acceptance. It was used to distinguish among three behavioural types of caribou in B.C. (northern, mountain, and boreal), between two in Alberta (mountain and boreal), between two in Ontario (forest-dwelling and forest-tundra), and two in Quebec (sedentary and migratory) (Bergerud 1978, Edmonds 1991, Heard and Vagt 1998, Harris 1999, Caribou Quebec 2000). Ecotypes are classes of populations adapted to different landscapes or environments as expressed primarily by their movements and feeding behaviour (Appendix 3). Thomas (1995) expanded the ecotype classification to include summer and winter habitat, migratory behaviour, winter food, and climate. The two northern metapopulations in the Southern Mountain population in B.C. (Hatter 2000) and populations in the Rocky Mountains and foothills of Alberta are the northern ecotype (Bergerud 1978, Edmonds 1988, Heard and Vagt 1998). Those ecotypes in B.C. and Alberta do not conform with (COSEWIC boundaries. However, ecotype criteria are not absolute as terrestrial lichens are supplemented with arboreal lichens in most local populations. Bergerud (2000) recognized sedentary/migratory and montane/boreal ecotypes. Reindeer in Russia were typed as forest montane, forest sedentary, forest migratory, forest-tundra migratory (Baskin 1990), and tundra.


Taxonomy and Systematics of Caribou

The systematics (evolutionary and genetic relationships) and taxonomy (classification) (Cronin 1993, 1997) of caribou is uncertain below the species level. In 1961, Banfield reviewed the global taxonomy of Rangifer. He concluded that all forms would be able to interbreed and therefore were one species, tarandus. His main criteria to separate subspecies were antler characteristics and measurements of skulls of fully grown members of both sexes. Banfield (1961) noted clines from south to north in size and pelage tone. He lumped all extant woodland caribou in North America into one subspecies, caribou. There were non-significant differences in “statistical populations” that he termed demes and “incipient subspecies.” Included were terraenovae in Newfoundland, caboti in northern Quebec and Labrador, sylvestris in boreal forests from Quebec to the southern mountains in B.C., and osborni in mountains of northern B.C., southern Yukon, and NWT. Those were considered to be subspecies by earlier workers (Kelsall 1984). Banfield (1961) viewed former subspecies osborni and caboti and caribou in the Hudson Bay Lowlands as demes that were intermediate between woodland and barren-ground caribou but placed them with caribou. He followed Jacobi (1931) in separating barren-ground caribou from woodland caribou on many semi-objective criteria and named them after the cross-sectional shape of antlers, i.e., cylindricornus and compressicornus, respectively. The taxonomic value of antlers has received little attention in spite of the potential expressed by Bubenik (1975) and explored by Butler (1986).

Geist (1991) argued that geography and craniometry were not taxonomic criteria and size was a poor one. He proposed that characters of hair color, gland patterns, and antlers, i.e., “social insignia,” at breeding should be used to identify subspecies. He proposed that “woodland caribou” (R. t. caribou) comprised populations in the mountains of central and southern B.C. and Alberta and in the boreal forest east of the mountains. Included were caribou in deep-snow zones of southern B.C. where long-strand arboreal lichens were the main food. In his opinion, caribou in northern B.C. (north of the Peace River) and Yukon were sufficiently different morphologically to warrant separate subspecies designation (R. t. osborni). Newfoundland caribou (R. t. terraenovae) differed ecologically through isolation in a different environment, including predation by lynx (Lynx canadensis) after wolves (Canis lupus) were extirpated early in the 20th century. He considered migratory caribou (R. t. caboti) in Labrador an intermediate deme (subsequently known as the George River population). Finally, he agreed with Cowan and Guiguet (1965) that the extinct Dawson’s caribou (R. t. dawsoni) was a separate subspecies.

Geography and vegetation are important for they can isolate populations, which then become subject to genetic drift and inbreeding, as shown for bighorn sheep (Ovis canadensis) (Fitzsimmons et al. 1997). In reality, geography/vegetation means islands of suitable habitat. Natural and sexual selection of caribou in different environments may also result in genetic differences. Geographic or political boundaries rather than subspecies can be used in regulations. For example, it is better to stipulate that caribou may not be killed in a defined geographic area rather than specify that a certain subspecies or population of caribou is protected. In the case of animal parts and meat, the best legal tools are chemical differences, including DNA fingerprinting. Management of lands is based on geographic and political boundaries and therefore geographic populations are the most practical entities for caribou conservation and management.


Studies of Genetic Lineage in Caribou

Transferrin (a blood protein) alleles found at a single locus suggested that a single subspecies, R. t. caribou, occupied mainland eastern Canada and Newfoundland (Røed 1992). A preliminary genetic analysis of a few samples suggests that the caribou of Gaspé were either isolated for a long period of time or their ancestry was different (Røed et al. 1991, Crête et al. 1994). However, a single locus with high variability and subject to rapid change is not a reliable indicator of phylogeny (Røed et al. 1991).

Another study found significant variation in transferrin allele frequencies among nine populations throughout the range of woodland caribou (van Staaden et al. 1995). Relatively little genetic heterogeneity occurred within populations. Geographic and genetic distance were significantly related. Isolated small populations tended to have four or fewer transferrin alleles.

Cronin (1992) assessed variation in mitochondrial (mt) DNA of woodland caribou from Alberta, northern Labrador (George River), and Newfoundland. He found considerable variation, though the sequence divergence of genotypes was low. He concluded that characteristic genotypes existed in caribou from different geographic areas (Cronin 1992). He concluded that classification below the species level for caribou and other cervids should include mitochondrial and nuclear genetic data, morphology, distribution, and natural history.

Another study of mtDNA indicated that all caribou in Canada originated from northern and southern clades (groups) isolated about 49 000 years ago during the Wisconsinan glaciation(Dueck 1998). Glacial advances occurred in the Canadian Rockies 75 000-64 000 and 20 000-11 000 years ago (Gadd 1986). Two groups of caribou were separated between those early and late Wisconsinan episodes and distinct clades evolved in isolation. Upon melting of the large continental glacier, the two groups spread out across Canada and their distributions overlapped.

The following scenario is deduced from the results for mtDNA (Dueck 1998). The isolated southern clade moved northward, as the continental (Laurentide) glacier wasted, to occupy all boreal forest and taiga in eastern Canada. In the west, they supposedly advanced as far north as the Mackenzie Delta through an inter-glacial corridor east of the Cordilleran Mountains. Caribou in the northern clade were isolated in the Beringia refugium in Alaska, part of Yukon, and Banks and Prince Patrick islands. They spread southward in the ice-free corridor and later in the mountains after the Cordilleran ice sheet melted, to the U.S. border and beyond. In the north, they also spread eastward to occupy all the tundra and taiga and northward into the Canadian Arctic Islands.

Many of the local populations along zones of contact and overlap contain haplotypes from both clades (Fig. 2). For example, the sample from the George River population contained 22% of the northern haplotype (all mtDNA is maternal and therefore haploid). The greatest mix of haplotypes is in the mountains of B.C. and adjacent Alberta where 75% of haplotypes in analysed samples are from the northern clade. Present-day woodland caribou apparently have evolved from both clades and introgression of DNA occurred where the two clades met and overlapped in distribution. Those results support COSEWIC’s separation of Mountain and Boreal populations. Caribou in the Cordilleran Mountains may have to be reclassified.

Some taxonomists believe that a subspecies must be monophyletic. The southern haplotype is 95% monophyletic but the northern haplotype is monophyletic or paraphyletic depending on the statistical analysis used to classify it (Dueck 1998, Dueck and Strobeck pers. comm.). Monophyly was more likely than the alternative.

The southern clade was the primary founding source for subspecies caribou in boreal and taiga forest east of the Cordilleran Mountains. One possibility is that the southern clade evolved in eastern North America centred on the Appalachians. Caribou from the northern clade travelled south in the ice-free corridor and eventually spread into the Cordilleran Mountains. Introgression of the southern haplotype into caribou in the Rocky Mountains may have occurred long after the ice sheets melted. Preliminary conclusions of another study of mtDNA support the hypothesis that eastern woodland caribou were isolated historically from caribou in the arctic and current subspecies are not consistent with observed genetic variation (Eger and Gunn 1999, J. Eger pers. comm. 2001).

Kushny et al. (1996) used microsatellite DNA (msDNA) to survey the genetic variation in populations of caribou across Canada. Four polymorphic loci revealed high levels of heterozygosity (>0.74) in all study populations (Kushny et al. 1996). Nuclear msDNA analysis was concluded to have a "very high potential for identifying individuals in respective populations." Subsequently, three local populations of woodland caribou in Yukon were found to differ genetically based on msDNA (Zittlau et al. 2000), as did three sub-populations of the Bluenose population of barren-ground caribou (Nagy et al. 1999), and others (Zittlau et al. 2001).

Caribou in northern B.C. and Yukon may either be included with granti or groenlandicus or receive subspecies rank once again as suggested by Geist (1991). They have a pelage similar to barren-ground caribou (R. t. granti) in the Porcupine population and formerly had subspecies rank as osborni (Cowan and Guiguet 1965). Caribou in the Southern Mountain population, where northern haplotypes predominate, may also be included with granti based on phylogenetic relationships. Collectively “mountain caribou” in B.C. and Alberta are more closely related to Alaskan barren-ground caribou than to woodland caribou, as concluded by K.H. Røed (pers. comm. 1998).

Caribou are genetically highly variable (polymorphic and heterozygotic) and apparently have evolved convergent behaviour and phenotypes within both clades. A sample from the George River population had 78% southern haplotypes but its appearance and migratory and social behaviour of wintering in the taiga, migrating to tundra range to calve, and forming large post-calving groups is similar to behaviour of the Qamanirjuaq, Beverly, Bathurst, and Bluenose populations of barren-ground caribou. The latter populations collectively have 6% southern haplotypes (Dueck 1998). The migratory behaviour of the George River and Leaf River populations is more likely a behavioural adaptation by resident woodland caribou rather than learned from northern immigrants. All the forest-tundra ecotypes sampled to date are mixed haplotypes. Mixed populations are expected where haplotypes meet and phenotypic differences may or may not be evident. Cronin et al. (1991) suggested that a mixed population of mule and black-tailed deer (Odocoileus hemionus spp.) should not be included in either subspecies. So, what about mixed populations of caribou? A pragmatic solution is to place mixed populations in the woodland taxon if southern haplotypes outnumber northern ones.

Though there are exceptions, one can place local caribou populations into two major ecological groups (ecotypes) depending on where they spend most of the summer -- alpine/tundra and forest. Those groupings are representative of most current local populations derived from northern and southern clades (Dueck 1998), respectively. This split makes sense ecologically, for tundra and alpine are similar habitats. Some of the alpine/tundra populations spend part of the winter in taiga or subalpine forest. The upper subalpine is analogous to taiga. Most mountain/tundra caribou are migratory but travel distances vary greatly. In the mountains, a caribou can travel from montane through lower and upper subalpine to alpine summer range in as little as 5 km. A forest tundra caribou that wintered in the boreal forest may have to travel 400 km through taiga and another 400 km on tundra to a suitable calving area and summer range.

Exceptions to the above groupings occur within forest-dwelling woodland caribou populations. Because of exceptions to general rules, no behavioural classification system using cover type, or migration/movements, or winter forage clearly stratifies populations of caribou. The George and Leaf river populations in Quebec/Labrador and the Hudson Plain, Pen Island, and Cape Churchill populations fit better in the forest (taiga)-tundra ecotype in terms of their use of ecoregions (Appendix 3). On the plains east of the Cordilleran Mountains, all forest-dwelling populations tend to spend all or part of the summer in open fens, bogs, lakeshore, and islands in lakes and peatlands. Those habitats are analogous to tundra in some respects, for they are rich in succulent forage, are cooler, and provide some relief from predators and insects.

Caribou use taiga and tundra where available within the boreal forest. Forest-dwelling caribou tend to occur at highest regional densities where there are elevational gradients. In Alberta, seven local populations of boreal caribou are associated with elevated terrain termed the Northern Alberta Uplands Physiographic Region (Province of Alberta 1993). Vegetation on the top of the Cameron Hills, Caribou Mountains, and Birch Mountains is taiga-like and termed Boreal Subarctic in the ecoregions classification. A small upland in Saskatchewan, the Wappaweka Hills, is frequented by a few groups of caribou with links to a large peatland to the south. Other populations such as the Red Wine Mountains (Brown et al. 1986) and the Gaspésie (Ouelett et al. 1996) include alpine tundra and subalpine or taiga in their ranges. For some populations, availability of suitable summer range appears to be more important than availability of winter range within their distribution. Of course that could change as forests used in winter are exploited.

More DNA samples are required from all populations to establish phylogenetic relationships. The date and location of all samples must be stated in all reports and publications. Some existing results may not be from the purported population because of overlap in winter distributions. Reliable samples are from calving areas of populations and tissues from dead calves and antlers cast by females about the time of calving, or from radio-collared individuals whose movement pattern is known.


Description

Woodland caribou are dark brown with a white mane and some white on their sides. Height at the shoulder is 1.0-1.2 m and mature females and males usually weigh 110-150 kg and 160-210 kg, respectively. Some characters suggest that Rangifer is an ancient member of the deer family, Cervidae (Banfield 1974). Both sexes bear antlers though up to half of females may lack antlers or have one antler. Antlers are flattened, complex, compact, and relatively dense compared with those of barren-ground caribou. A distinctive characteristic of all caribou is large, rounded hooves that reduce sinking in snow and wetlands and act as shovels when digging for food under snow. The ‘dew claws’ are large, widely spaced, and set back on the foot, which greatly increases weight-bearing area and reduces ‘foot loads.’ Banfield (1961, 1974), Miller (1982), Kelsall (1984), Geist (1991) and Bergerud (2000) described physical features of woodland caribou.


Nationally Significant Populations

According to (COSEWIC (2001) guidelines, as amended from 1994 guidelines, any group below the species level can be considered for designation when it meets the following criteria:

  1. When a population is considered to be genetically distinct based on genetic analysis, taxonomic techniques, or other compelling evidence.
  2. When a population is geographically distinct and meets either of the following criteria:
    • The population represents a significant portion of the historic range of the species in Canada; or
    • The population is the sole representative of a biological species at risk within any of Canada's major biogeographic zones.

Additionally, the population must be of national significance. Populations in the NEAs are assumed to have behavioural adaptations to those environments and therefore are nationally significant (Shank 1998). They are assumed to be evolutionary significant units (Ryder 1986).

COSEWIC populations conform to Banfield’s (1961) demes except that he grouped mountain caribou in central and southern B.C. with the boreal deme sylvestris. Woodland caribou in Newfoundland were considered an incipient subspecies by Banfield (1961), of subspecies rank by Geist (1991), and were designated as a separate population by Kelsall (1984). They differ from mainland caribou in terms of genetics, ecology, and parasitism (Røed et al. 1991, Dueck and Strobeck pers. comm., Ball et al. 2001).

With those changes, forest-dwelling ecotypes of subspecies caribou can be grouped as follows (relative to Kelsall’s 1984 divisions):

  1. Northern Mountain population (formerly part of the western population)
  2. Southern Mountain population (formerly part of the western population)
  3. Boreal population (part of former western population plus boreal and southern taiga populations in Ontario, Quebec, and Labrador).
  4. Newfoundland (Island) population (formerly part of eastern boreal).
  5. Atlantic (Gaspésie) population (formerly Gaspé population)

The boundary between forest dwelling (threatened) and forest-tundra (not at risk) ecotypes in Ontario (Harris 1999) bisects the Hudson Plain at about 53o N latitude. In Quebec, the northern boundary of sedentary (forest-dwelling) caribou (Caribou Quebec, 2000) is at about 54o N latitude.

Each jurisdiction has an obligation to conserve caribou. World and national approaches should help governments set priorities for conservation based on how they fit into larger scales. Clearly there is need for inter-jurisdictional cooperation for transboundary populations. Historically, gene flow was possible throughout most of the range of woodland caribou. Fragmentation of habitats now restricts gene flow. Pro-active management of landscapes will be necessary to maintain some degree of connectivity among local populations.




Footnotes

1 Thomas Wildlife Services
46 Pineview Drive
St. Albert, AB
T8N 4S8


2 Grayhound Information Services
3107 8th Line Road
Metcalfe, ON
K0A 2P0