Marmot

Abstract: Social groups of alpine marmots (Marmota marmota) were studied for 7 years. The groups consisted of a territorial pair and up to 18 lower ranking animals of various ages, mostly the pair's offspring (Tables 1, 2). Group members lived in a common home range and always hibernated together in one hibernaculum. Groups with older, subordinate animals experienced slightly higher summer mortality but significantly reduced winter mortality (Fig. 1). Infant winter mortality was further decreased if most older subordinates were potentially their full sibs (Fig. 2). Subordinate group members lost less mass during winter with increasing size of the hibernating group, but this trend was reversed when infants were present. Furthermore, augmented mass loss due to low hibernaculum quality became evident (Fig. 3). Apart from these effects, the presence of infants caused additional mass loss in potential full sibs. The opposite was found in subordinates certainly descending from other parents than those of the infants (Table 3). Winter mortality and mass loss data revealed (i) a general benefit of joint hibernation, (ii) an unavoidable cost of infants' presence to other group members, (iii) that only potential full sibs helped in warming infants, (iv) that helping was energetically expensive and increased infant survival. The evolution of postponed dispersal in ground-dwelling squirrels has been attributed to the direct fitness gained by enhanced reproductive chances of offspring when not expelled from the natal territory (Armitage 1981, 1987, 1988). This study shows that group living in alpine marmots has benefits during winter and indicates the additional importance of kin selection in marmot social evolution.

Abstract: Marmot (Marmota flaiiventris) populations are colonial or satellite. The num- ber of adults of colonial populations is relatively stable; fluctuations occur primarily because of changes in numbers of young and yearlings. Population trends among five colonial popula- tions are dissimilar. Satellite populations are unstable and reproduce at a lower rate than do colonial populations. Satellite marmots are shorter resident than colonial marmots. Both colonial and satellite females usually are longer resident than males. All adult colonial males and 41% of adult colonial females are recruited from other places; all satellite adults are recruited from other places. Losses of colonial marmots are attributed primarily to mortality during hibernation and emigration. Predation appears to be a minor source of mortality of colonial marmots, but may be of greater significance to satellite populations. Demographic relationships of individual colonies appear to be density-independent. Dispersal of colonial animals occurs primarily among yearlings, which have a higher expectation of reaching sexual maturity than young have. The major cause of dispersal is social pressure, but social stress is not simply density-dependent. The colonial social organization is more adaptive than the more nearly solitary (-_ satellite).

Abstract: Behavioral and environmental factors in the spatial distribution and population dynamics of a yellow-bellied marmot (Marmota flaviventris) population were studied in 1971 and 1972 in Gunnison Co., Colorado. Yellow-bellied marmots are generally considered to be colonial; however, this is not their only option, depending upon the marmots' behavioral profile and the size and composition of the habitat. Of the adult-yearling group 75% lived as members of colonies, 16% lived at satellite sites, and 8% were transients. Satellite sites differed from colonies mainly in size and topographic diversity; they may be considered mini- habitats, with the most limited resource being burrow sites. Marmots can be classified, by means of mirror-image stimulation (MIS), as aggressive, social, and avoider. Aggressive females tended to occupy small harems at large sites, or to live as solitary individuals regardless of the size of the site. Social females occurred primarily at large sites, in harems. Avoider females lived in peripheral burrows at colonies, or in satellite sites. All behavioral types reproduced successfully, but reproductive fitness was cor- related with social structure. Aggressive females were most fit in small harems or at satellite sites, whereas social females were most fit in large social groups. Avoiders were least fit in all social situations. Data presently available fails to show that the behavioral profile of the female is reflected in the social tendencies of her young. In general, social behavior is a major factor affecting the distribution and dynamics of populations of yellow-bellied marmots, but dispersion is also related to the distribution of suitable habitat.