Population-level response of Marmota flaviventris to a middle Pleistocene climatic warming event in the Colorado Rocky Mountains [Réponse populationnelle de Marmota flaviventris à une période de réchauffement climatique du Pléistocène moyen dans les Montagnes Rocheuses du Colorado].

Résumé

We used morphological details of dentition to track populations of the yellow-bellied marmot, Marmota flaviventris, through approximately 100,000 years. Fossil teeth and jaws from the Pit Locality, Porcupine Cave, Park County, Colorado, were sorted into seven temporal intervals that most likely range from 750,000 to 850,000 years old and span at least one glacial-interglacial transition. For fourth premolars and the third lower molar in each time interval we determined mean length, width, and proportions. Log(area) of the upper fourth premolar (which we regressed against skull length in modern specimens) provided estimates of body size. Many of the traits changed in mean or variance through time, but the changes were largely independent of one another even for traits on the same tooth, suggesting random variation of independent characters that probably are selectively neutral. As population size relative to other ground-dwelling squirrels (Cynomys and Spermophilus) decreased at the transition from a glacial interval to an interglacial, body size significantly increased and the number of morphological changes may have become slightly more pronounced. At that time there may have been selection for larger animals because of the interaction between climatic parameters, length of growing season, metabolic rate, and hibernation.