Struttura sociale e strategia di fitness nelle marmotte. Social organization and fitness strategies of marmots [Organisation sociale et stratégies sélectives des marmottes].

Résumé

Marmots (Marmota spp.) occur in various social groupings : woodchucks (M. monax) are essentially solitary (Barash 1989: 167). Yellow-bellied marmots (M. flaviventris) form female kin groups to which a male is attached to form a harem (Armitage 199l, Olympic (M. olympus) and hoary (M. caligata) marmot groups consist of a male and usually two adult females that reproduce in alternate years (Barash 1973, 1974a) and the alpine marmot (M. marmota) groups contain one pair of breeding adults plus a variable number of non-breeding 3 and 4 year-old adults (Arnold 1990a). In all species, dispersal typically occurs the year before reproductive maturity is reached, but subordinate, non-breeding adults may remain for one or more additional years in alpine marmot groups (Arnold 1990b). Increasing sociality in marmot groups was correlated with the length of the growing season where the growing season is too short to permit animals to become reproductively mature at l year of age, offspring are retained in their natal area for one or more additional growing seasons (Barash, 1974b). Subsequently, delayed dispersal and the consequent retention of offspring in their natal area were viewed as a life-history tactic whereby females continue reproductive investment beyond weaning (Armitage 198l). Among North American ground-dwe1ling sciurids, variation in sociality was best explained by age of first reproduction and age adult body mass was reached where the growing season is too short to permit animals to become reproductively mature at l year of age, offspring are retained in their natal area for one or more additional growing seasons (Barash, 1974b). Subsequently, delayed dispersal and the consequent retention of offspring in their natal area were viewed as a life-history tactic whereby females continue reproductive investment beyond weaning (Armitage 198l). Among North American ground-dwe1ling sciurids, variation in sociality was best explained by age of first reproduction and age adult body mass was reached 1987, 1991. Michener 1983) indicate that sociality is a fitness strategy.