The evolution, ecology, and systematics of marmots
The first species of Marmota occurred about 9.5 MYA in the United States. All modern species are known from the Pleistocene where they lived in the periglacial zone. With the retreat of the glaciers and expansion of forests, marmots became restricted to open mountain landscapes or the forest steppe or plain steppe zones. Marmots became adapted to habitats with grassland for foraging, a slope providing good drainage, southern to eastern exposure, and a soil structure appropriate for burrowing. Marmots adapted to habitats characterized by a seasonal food shortage, low temperature, and precipitation as snow by hibernating for an average among species of 7.2 months. Environmental harshness is characterized by large home ranges and reproductive skipping and the evolution of large body size, which increases the efficiency with which fat is utilized. A major consequence for this large animal living where the active season is short is that at least one additional summer of growth is necessary for young to reach maturity. Young are retained in their natal areas; this delayed dispersal results in the formation of social groups. Four types of social groups may be recognized: solitary, female kin group, restricted family, and extended family. Sociality evolved at least twice in marmots, once in North America and once in Eurasia. In those species that form extended families where dispersal is delayed beyond reproductive maturity, subordi- nate adults may engage in alloparental care and polyandry may occur. Evidence that marmot populations adapt to local conditions indicates that population differentiation continues and that there may be more species than the currently recognized fourteen.
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