Wildlife
The failure to recognize distinct species and subspecies of caribou is hampering efforts to conserve them. So, I revised their taxonomy.
In the dream, I am on a saddle horse leading a string of packhorses up a mountain trail. Moose look up from the willows along the creeks. Grey specks in alpine meadows are Stone’s sheep. On cliffs are mountain goats. And everywhere above the tree line are caribou: singles or small groups. In a high mountain pass, 20 caribou laze on a late snow patch in the lee of a peak, avoiding flies. Then I wake up and realize it’s not a dream; it’s a memory.
These were Osborn’s caribou, the largest subspecies of caribou, which can weigh up to 340 kilograms. I was guiding for big game in the northern Rocky Mountains of British Columbia. As a mammalogist, I’ve studied mountain caribou, woodland caribou in the boreal forest of northern Alberta and the N.W.T., barren-ground caribou in northern Yukon and Nunavut, and the Peary caribou, the smallest caribou subspecies, in the High Arctic islands. I’ve also photographed Rocky Mountain caribou in Banff and Jasper National Parks and tundra reindeer in Norway. Since 1961, all these varieties of caribou have been lumped together under just one species, Rangifer tarandus. This has caused conservation problems because most caribou subspecies are not recognized under Canada’s Species at Risk Act. Conflating multiple species and subspecies into one makes it difficult—practically and legally—to develop conservation plans and regulatory protections specific to each.
In a recent paper in the journal ZooKeys, I restored two of the Canadian subspecies back to full species status, and restored subspecies status to Osborn’s caribou, Labrador caribou, Selkirk caribou, Rocky Mountain caribou and Newfoundland caribou. While taxonomy changes are not usually headline news, this is a big change for biodiversity in Canada, which has about half of the world’s caribou species and subspecies (the other half live in Europe and are called reindeer).
One can still watch a single herd of more than 200,000 caribou in migration, an unparalleled wildlife spectacle. Most populations, however, are declining or endangered, creating constant tension between conservationists and resource extraction interests. This revision will impact Canada’s Species at Risk Act, which has been hamstrung by obsolete caribou classifications.
Canadians think we know caribou: an image of one is on our quarter. Its antlers, sweeping back, then up and forward in a long arc nearly devoid of tines to a palmated top, show it to be an Arctic barren-ground caribou, Rangifer arcticus, one of two species found in Canada based on my recent taxonomic revision. Rangifer arcticus has eight subspecies. The other species is woodland caribou, Rangifer caribou, with three subspecies.
Besides differences in genetics, appearance, ecology, and behaviour, a central criterion of species definition is reproductive isolation. The newly re-defined species, and even most subspecies, almost never breed with one another, even where their rutting ranges overlap; or if they do, their calves do not survive. This is true of semi-domesticated reindeer and Eurasian tundra reindeer both in Europe and where they have been introduced to Alaska, the Northwest Territories and Nunavut; of barren-ground caribou and woodland caribou; and of Eurasian forest reindeer and tundra reindeer. So, what distinguishes Canada’s caribou species and subspecies?
Barren-ground caribou calve synchronously as a predator-avoidance strategy. To calve synchronously, they must form large rutting aggregations, where males tend individual females. After calving, they aggregate and wander. I once stood on a mountain top in northern Yukon and counted 60,000 in a single herd draped over mountains and valleys to the coast 20 kilometres distant. Barren-ground caribou migrate hundreds of kilometres from their winter range in the taiga to tundra calving grounds near the Arctic sea coast. Because males do not defend harems, their infrequent combats are brief and perfunctory; their antlers, with the long, thin beams depicted on our quarter, are a visual stimulus to attract females. They are pale and are about half the size (males average 110 kilograms, up to 153 kilograms) of Osborn’s caribou and two-thirds the average size of woodland caribou.
DNA analysis shows that western montane populations, previously considered to be ecotypes of woodland caribou, share a common ancestor with barren-ground caribou, but distantly, having diverged some 60,550 years ago, during a warm interval long before the last Ice Age glaciation. Since then, the caribou of the barrenlands have evolved further, developing a host of adaptations for long-distance migration, synchronized calving (a predation-avoidance strategy), extreme cold, bright tundra environments, and 24 hour/day darkness in winter and daylight in summer. The montane ecotypes grew larger in size and evolved a mating system (harem-tending), dispersed calving and short, altitudinal migration patterns more suited to alpine pastures in summer and dense forest in winter. Their shared lineage makes them all subspecies of Arctic caribou, which now include mainland barren-ground caribou, Peary caribou, Dawson’s caribou, Osborn’s caribou, Rocky Mountain caribou, Selkirk or mountain caribou, Grant’s caribou (restricted, as originally described, to the west end of the Alaska Peninsula and archipelago), and Stone’s caribou of southern Alaska mountains. All of these were originally described as full species.
Archaeologists distinguish “modern” tundra reindeer and barren-ground caribou from primitive forms—living and extinct—that did not have adaptations to extreme cold and to long-distance migration. They include a broad, high muzzle to increase the volume of the nasal cavity to warm and moisten the air before it enters the throat and lungs, bez tines set close to the brow tines, distinctive coat patterns, short legs and other adaptations for running long distances, and multiple behaviours suited to tundra, but not to forest (such as synchronized calving and aggregation during rutting and post-calving). As well, many genes, including those for vitamin D metabolism, fat metabolism, retinal development, circadian rhythm, and tolerance to cold temperatures, are found in tundra caribou that are lacking or rudimentary in forest types.
By contrast, woodland caribou, R. caribou, are darker and on average 63 per cent bigger (males average 180 kg, up to 272 kg) than barren-ground caribou (males average 110 kg, up to 153 kg). Because males tend harems and defend them from other males, they have shorter, straighter, more robust, and bushier antlers designed for combat. DNA analysis shows woodland caribou diverged from primitive ancestors of barren-ground caribou, not during the last glacial maximum, 26,000 to 19,000 years ago, as previously assumed, but in the mid-Pleistocene, around 357,000 years ago. At that time, modern tundra caribou had not yet evolved. Woodland caribou are likely more closely related to extinct forest caribou species than to barren-ground caribou. For example, the extinct species Torontoceros [Rangifer] hypogaeus, had features (robust and short pedicles, smooth antler surface, and high position of second tine) that relate it to forest caribou. This being the case, woodland and barren-ground caribou cannot be the same species because they do not share a direct ancestor. Genetic distance between barren-ground and woodland caribou, as shown by many studies over the last 19 years, confirms them as separate species. Labrador or Ungava caribou, and Newfoundland caribou, although genetically, ecologically and behaviourally distinct from boreal woodland caribou, share the same ancestral lineage and are therefore subspecies of woodland caribou.
Likewise, in Eurasia, forest reindeer, Rangifer fennicus, descend from a fossil reindeer, Rangifer guettardi, that lived in western European forests, whereas all tundra reindeer descend from another fossil species, R. constantini, that was adapted to grasslands. Since they do not share a direct common ancestor, they cannot be the same species.
In the 1990s, the B.C. government augmented a declining Selkirk Mountain caribou herd with about 130 Osborn’s caribou from the west-central part of the province. These are both subspecies of Arctic caribou. Osborn’s caribou evolved to migrate to low elevation all winter and paw through the snow for “reindeer moss,” a ground lichen that grows under dry lodgepole pine, but not in the moist cedar-hemlock and spruce-fir forests of the Selkirk Mountains. Unlike the Selkirk Mountain caribou, they did not have the instinct to migrate back to subalpine forest in mid-winter to forage arboreal lichens. No Osborn’s caribou survived a year. This is proof of reproductive isolation.
When two recognizably different kinds of animals—deer, sheep, monkeys, whatever—cannot interbreed even when put together, and cannot survive in each other’s habitats, they are different species, regardless of what definition of “species” is in vogue. With caribou, DNA has forced us to accept the obvious and recognize the diversity of our caribou.
Lee E. Harding has a BSc in Wildlife Management from Humboldt State University (California) and a PhD in Wildlife Toxicology from Gifu University (Japan). He consulted in wildlife ecology in the Arctic for five years, was an Environment Canada biologist and program manager for 21 and, after taking early retirement from the Canadian Wildlife Service, was an environmental consultant for another 20 years. Dr. Harding is a Registered Professional Biologist in British Columbia, Canada and a member (retired) of the British Columbia College of Applied Biology, the American Society of Mammalogists and the British Columbia Field Ornithologists. His recent publications have included several journal articles on caribou.
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