The oral anatomy of Arctic ruminants: coping with seasonal changes

Abstract

We studied the feeding apparatus of three species of northern ruminants representative of three feeding types: muskoxen Ovibos moschatus, Norwegian reindeer Rangifer tarandus tarandus and high Arctic Svalbard reindeer Rangifer tarandus platyhrynchus and Siberian musk deer Moschus moschiferus. The shape of the muzzle, the incisor arcade, the incisiform and the molariform teeth indicate that these species are selective feeders, irrespective of their body size or their position on the grazer-concentrate selector continuum of feeding types. Narrow muzzles seem well adapted for selective feeding on the diminutive but highly nutritious plants, or parts of plants, on tundra swards and Arctic-alpine meadows and enable the animals to maximize nutrient intake during the short summer. However, their small mouths presumably also restrict reindeer and muskoxen to taking small bites, thereby achieving low rates of dry matter intake when feeding on the very short swards in winter. This is partially obviated by two general strategies; a reduction of energy requirements in winter and, in Norwegian reindeer, migration inland to where foraging conditions are generally more favourable. In Svalbard reindeer, which have little access to lichens or other easy digestible plants in winter, rumen ®ll increases through the accumulation of slowly fermenting ®brous foods. Despite their narrow muzzles, reindeer and muskoxen are unable to avoid ingesting a certain amount of poor quality forage in winter and cope with this by appropriate modi®cation of digestive function.

Where clocks are redundant: weak circadian mechanisms in reindeer living under polar photic conditions

“…Reindeer pursue a different strategy in winter. The small mouths which enable reindeer to feed selectively, plucking only the most nutritious parts of diminutive tundra forage plants, presumably also restrict them to taking small bites (Mathiesen et al 2000). Consequently, even setting aside the inherent constraints of ruminant digestion, reindeer are precluded from compensating for decreased abundance of forage by feeding in bulk.…”

Herbivore grazing—or trampling? Trampling effects by a large ungulate in cold high‐latitude ecosystems

“…This is, however, an overestimate, as step overlap likely would be considerable. Also, caribou may be selective feeders (e.g., Mathiesen et al, 2000) and the amount of damage may be less in terms of amount, although probably not any less in terms of food lost.…”

Variation at high latitudes: the geography of body size and cranial morphology of the muskox, Ovibos moschatus

“…Once classified as a grazer on the basis of rumen characteristics and a graminoiddominated diet (Staaland & Thing, 1991), muskoxen have more recently been recognized for their atypical oral morphology. The relatively narrow muzzle of Ovibos approaches that of a concentrate-selector, while its lower incisors and molariform dentition retain the characteristics of a grazer (Mathiesen et al, 2000).…”

“…Indeed, the link between processing requirements and postcanine tooth area has long been recognized (Gould, 1975). Mathiesen et al (2000) discussed hypsodonty in arctic ruminants, recognizing that high crowned teeth enable species to shear high fibre foods more efficiently, but little attention was given to the molar crown beyond this.…”

“…In the case of large ruminants, individuals may be constrained by the rate of processing food in order to reduce particle size to permit passage in the gut. Interspecific patterns, reflecting these selection pressures, have been reported in feeding behaviours (Klein, 1992) and morphology of the gut (Demment & Van Soest, 1985), mouth (Janis & Ehrhardt, 1988) and dentition (Mathiesen et al, 2000). Larger body sizes, larger rumens, wider mouths and lower relative rates of metabolism favour bulk feeding on forages of low nutritional value (Hanley & Hanley, 1980;Illius & Gordon, 1987;Hofmann, 1989;Adamczewski et al, 1994a).…”