Based Studies of Yellow - Bellied

Some fundamental biological questions can be answered only by taking an “ecology of place” approach—by studying a focal system over long periods of time. One of these fundamental questions is the degree to which population dynamics are a function of social behavior. Long-term studies of yellowbellied marmot populations of known pedigree have examined the role of kinship in social behavior and organization. Additional studies of physiological energetics, feeding behavior and nutrition, and hibernation revealed Place-Based Studies of Yellow-Bellied Marmots 135 how marmots adapt to life in a seasonal environment, while studies of genetics, dispersal, and demography uncovered the demographic variables that underpin local and regional population dynamics. My research team and I determined that these montane marmots live in mother-daughter-sister groups, or matrilines, that are defended by an unrelated male. The groups are localized near rocky outcrops that provide two limiting resources—suitable burrows for hibernation and predator escape, and access to meadow foraging areas. Population dynamics are largely a function of fertility and age of first reproduction. Both parameters are strongly affected by the social behavior of dominant females, who can delay reproductive onset in younger subordinates. Although by delaying reproduction subordinate females lose direct fitness that is not compensated by increased indirect fitness (fitness of relatives), the alternative of dispersing is worse: dispersal increases the probability of mortality and does not increase the likelihood of early reproduction. The fundamental reproductive strategy of a female is to join or form a matriline even if she faces possible reproductive suppression. Consequently, the survival and fecundity variables that drive the dynamics of local yellowbellied marmot populations result largely from the fitness-maximizing strategies of individuals. These same strategies determine the dynamics and persistence of the regional metapopulation because they cause large colonies to export individuals to vacant patches, which then become occupied by the new matriline. This case study, which has been rooted in a single location for more than 40 years, illustrates how population dynamics can be understood from the perspective of individuals acting to maximize their individual fitness in a patchy, seasonal environment.