Social organization, reproductive success and population dynamics in a high-elevation Yellow-bellied Marmot colony

Abstract

High elevation marmots have a short growing season caused primarily by prolonged snow cover. The short growing season may affect sociality and/or reproductive success. This proposal was tested by examining the social organization and reproductive success of a yellow-bellied marmot population at 3400m. The organization of females in mother: daughter: sister matrilines did not differ from that of marmot populations at about 500m lower elevation. Rates of recruitment and immigration in the high elevation population were similar to those of the lower elevation population. The major differences between the two populations was the much lower frequency of weaning and much higher frequency of failed reproduction (reproduction initiated, but no young weaned) in the high (alpine) elevation population than in the lower (montane) elevation population. During the seven-year study, only one female weaned litters in successive years. High frequencies of reproductive success were associated with years of early snowmelt and high frequencies of failed reproduction occurred in years of heavy snowpack and late snowmelt. A winter of low snow precipitation was associated with high mortality. The short growing season (late snowmelt) primarily affected reproductive success but did not affect sociality. Therefore, the proposal that the short growing season is associated with change in social structure of yellow-bellied marmots is rejected.