Socioecology of alpine marmots [Socioécologie des marmottes alpines].

Résumé

Alpine marmots have been studied since June 82 in Berchtesgaden National Park 230 animals have been marked. Every member of the 24 families in the main study area (l05 ha) is individually known. Marmots typically live in monogamous pairs with their offspring. Young usually disperse when sexually mature as 2-year-olds. Delayed dispersal or integration of strangers leads to groups with more than two adults. Mating occurs after hibernation, only the dominant female litters. Reproduction is not necessarily annual and, like litter size, depends on female body weight after hibernation. This weight is determined by both loss during hibernation and gain during the previous summer. Sex-ratio within litters is skewed in favour of males when hibernation weight losses are low. The most important 15 ecological variables were measured in each home-range and their influence on weight changes was tested. Factor analysis separated them into three categories : (l) abiotic conditions (e.g. radiation, thaw, soil moisture and mean soil temperature at the hibernacula during winter), (2) home-range size, (3) food quality within home-range. Mainly abiotic variables influence weight loss during winter and weight gain during summer. Thus, home-ranges with favourable hibernaculas are less suitable during summer, presumably due to thermal stress. Suboptimal wintering conditions might be counter-balanced by the fact that group members always hibernate together. In the lab body temperatures of all members of three groups were recorded during hibernation, using radiotelemetry. Torpor (12-16 days) alternates with short periods of activity (2-3 days), highly synchronized for all group members. Initial electrophoretic analyses of polymorphic allozymes to investigate the relationship within these groups showed that cuckoldry was present.