The effects of elevation on growth rates and body masses of yellow-bellied marmots [Effets de l'élévation sur les taux de croissance et la masse corporelle des marmottes à ventre].

Résumé

Growth rates of yellow-bellied marmots (Marmota flaviventris) vary significantly with sex, age and location. The accumulation of fat is strongly influenced by short growing seasons and marmots living at high elevations often have shorter active seasons than populations at lower elevation due to prolonged snow cover. We studied marmot populations at 2900 m elevation and 3400 m elevation to test hypotheses about effects of elevation on growth rates. We compared growth rates and emergence masses of marmots among age and sex classes from the two elevation sites. Juvenile growth rates did not differ significantly between populations and regression coefficients were very similar when corrected for weaning date. Emergence masses for yearlings at the high elevation site were significantly higher than the lower elevation site, nut there was no difference in growth rates. However, there were sex differences in growth rates of yearlings. Male yearlings at the high elevation site had significantly higher growth rates compared to low elevation yearling males. Low altitude yearling males were twice the size of high altitude yearling males at the beginning of the summer; the higher growth rates in high altitude population reduced the mass differences between the two groups prior hibernation. Adult growth rates and masses were not significantly different between elevation sites. Differences in the length of active seasons between both sites may be the strongest influence on variation in growth rates and masses between the populations of marmots.