Abstract. Marmot (Marmota flaiiventris) populations are colonial or satellite. The number 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 populations 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).

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org. ABSTRACT:Seasonal changes in the body weights of yellow-bellied marmot (Marmota flaviventris) populations were studied for 8 years in western Colorado. Marmots may be classified by size into four age groups: juvenile, yearling, 2-year-old, and 3-year-old or older, each group with significantly different mean body weights. For each age group, the mean body weight of males was significantly larger than that of females. Mean body weights in June of yearlings and older were smaller, the later the onset of the growing season. All age groups made significant weight gains each year; there was no significant difference in growth rates among years. When the rates of weight gain of juveniles are corrected for time of appearance aboveground, the regression coefficients are virtually identical. The earlier young marmots are weaned, the more they weigh at hibernation and the more likely they are to survive hibernation. The percentage of young surviving their first winter of hibernation is significantly greater the earlier spring begins. Marmots at 3400 m elevation had growth -rates similar to those of marmots at 2900 m elevation.The adaptive strategy of marmots includes rapid growth rates, high tissue growth efficiencies and extension of the growing season by reproducing immediately following hibernation.

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Optimization models have been widely and successfully used in evolutionary ecology to predict the attributes of organisms. Most such models maximize darwinian fitness (or a component of fitness) in the face of trade-offs and constraints; the numerical results usually depend on the exact form of the trade-offs/constraints. Here we report the first (to our knowledge) numerical optimum for life-history evolution which is independent of the details of the underlying trade-off, for a large array for trade-off forms. The rule is that at small litter sizes, the range in offspring size is inversely proportional to the size of the litter. Details of the offspring-survival/offspring-size trade-off set the value of the proportionality constant, but the -1 exponent, the inverse proportionality itself, is universal. Studies of life histories have yielded many empirical examples of universality for various scaling exponents (for example, adult lifespan scales as approximately 0.25 with adult body mass within many taxa); this is an example of the numerical value of an exponent (here -1) emerging from a life-history model as independent of all but a few general features of the underlying economic structure.