Ecologie hivernale des Lemmings et fluctuations de leurs populations
International audience In this paper I have suggested that the populations of Lem mings are normally held at low levels by adverse environmental factors, chiefly factors associated with snow. However, the fertility of these animals is so great that if there is a temporary relaxation in the environme...
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| Format: | Article in Journal/Newspaper |
| Language: | French |
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HAL CCSD
1967
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| Online Access: | https://hal.science/hal-03531614 https://hal.science/hal-03531614/document https://hal.science/hal-03531614/file/bitstream_118980.pdf |
| Summary: | International audience In this paper I have suggested that the populations of Lem mings are normally held at low levels by adverse environmental factors, chiefly factors associated with snow. However, the fertility of these animals is so great that if there is a temporary relaxation in the environmental control mechanism, a population peak can be produced in a few months — a period of winter breeding, followed by a normal summer reproductive period. There appear to be two critical periods in the year. The fall critical period begins with « thermal overturn » and ends with the « hiemal threshold ». Pruitt (1957) has shown that the former occurs at about the same date each year because it is a function of latitude whereas the latter may be quite variable. During the critical period much of the tundra becomes unsuited to Lemmings because both soil and air temperatures are below 0°C and no insulating blanket of snow is present. There will, however, be favorable microhabitats — in the hollows where the first early snow accumulates for example — and I suggest that the size of the overwintering population depends directly upon the number of such favorable microhabitats, ie. the « carrying capacity » is not related either to food supply or population density. The autumn period probably also governs the quality of the food available to the animals during the winter. Given a sufficient snow cover and food of adequate quality, Lemmings reproduce under the snow. The second critical period occurs in the spring at about the time of the melting of the snow. Again, the number of secure microhabitats may be reduced, this time by flooding of the lower sections. At that time of year reproduction invariably stops, and many deaths may occur. If the unfavorable period is prolonged, growth of the overwintered animals and the beginning of summer breeding are both delayed. Thus to produce a Lemming outbreak the following sequence of events should occur : 1) vegetation should be quick-frozen in order to preserve its nutrient value 2) ... |
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