Holarctic Marmots as a factor of Biodiversity.
Rumiantsev V.Yu;, Nikol'skii A.A. & Brandler O.V. eds.,
3d Conference on Marmots (Cheboksary, Russia, 25-30 August 1997),
Moscow ABF 1997, 216p. : 8-9.
HETEROGENEITY OF DEVELOPMENT IN MARMOTS: ONE OF THE BASIC FEATURES
OF POPULATION DEMOGRAPHY AND REPRODUCTION
Severtsov' IPEE RAS,
Heterogeneity, observed in marmot (Marmota) populations provides wide spectrum of genetic trends, capability to adapt to natural cycles, widespread dispersion over various landscape zones of Holarctica and as a result - flourishing in conditions of climatic shocks in late Pleistocene.
Important part of heterogeneity in marmot populations is heterogeneity of young marmot development during 2-3-year long growth, late maturation, complex sex composition and essential social effects, suppressing or supporting start of reproduction. Heterogeneity can be observed even among the newborns of the same litter. Thus, body length varies in steppe marmot and Mongolian marmot from 9.4 to 11.0 cm (weight 31-41 g), in grey marmot - 7.5-9.6 cm (weight 28.7-34.2 g), in Yakitian black-capped marmot - 10.3-11.3 cm (weight 28.6-39.7 g). By the time of emerging above ground the difference increases (Bibikov, 1967), one can easily observe smaller pups ("starvelings").They can not compete for better feeding with bigger and more active litter mates (Tarasov, 1961).
Difference in size in yearlings is the same as in juveniles in the first summer of life. Heterogeneity of development in yearling marmots is observed in dentition,cranium, gonads (Cherviakova, 1980). Half of grey marmots do not survive, and litter size (n=76) reduces from 4.2 pups in late May to 2.1 in June-August (Bibikov, 1967), however the heterogeneity in marmot body size is kept. Size heterogeneity, observed in yellow-bellied marmots, may be a result of prolonged birth period - pups from later litters do not survive hibernation, quota of survived pups in these group is three times less than in earlier litters (Armitage, Downhover, 1974).
By the end of second summer of life population of yearling marmots appears "divided" by size and development of animals, although the most underdeveloped marmots were eliminated. In the 3-d and 4-th summers growth of maturating marmots slows down (body length increment is 1-2 cm, or 4%, per year) and season fluctuation of weight depends on fat stock (Cherviakova, 1980). Actually, slowing down and leading of marmot development make population structure more complex, and social relations in families result in variety of time of dispersion and setting of new families, in female reproduction rate, i.e. in population reproduction. Rate of reproduction and rate of mortality also correlate with population density: average number of placental spots in females (M m) is: in conditions of density 10-5 marm./sq.km - 6.4 0.13; 40-60 marm./sq.km 5.6 0.2; 120-150 marm./sq.km - 5.0 0.38. Respectively, quota of breeding females decreases is 75% in conditions of low density to 47.1 - in high density (Pole, 1991).
Growth of population heterogeneity on the base of heterogeneity of development of young animals helps marmots in extreme conditions. At the same time, particular species form different adaptations of buffer nature, including capability of weaker marmots to stop their growth to provide better fat accumulation, incomplete moulting, more efficient uninterrupted hibernation, increase of reproduction rate in conditions of "short summer". Such adaptations permit young marmots to change diet and time of foraging, to limit energy waste in hard seasons and other.
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