Organisms of the northern alpine tundra probably evolved before those of the Arctic tundra, appearing first in the Mongolo-Tibetan Plateau. Few alpine animals, however, contributed directly to the evolution of Arctic tundra species, because physical barriers prevented the migration of species and because alpine and Arctic animals were specialized to their particular environments. However, alpine plants and some animals migrated east and west through mountain ranges to Europe and North America.
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The meadow vole (Microtus pennsylvanicus) is one of the most common mammals in North America. Its geographic range spans most of Canada and the conterminous United States as well as most of Alaska.
Lowland tundra animals appear to have evolved in central Eurasia when tundra replaced the cold temperate steppe. These animals migrated west to Europe about one million years ago, during the middle of the Pleistocene Epoch, and later migrated east to North America across the Bering Land Bridge. As a product of this migration, many of the common Arctic animals are circumpolar. Such animals include the polar bear (Ursus maritimus), Arctic fox (Alopex lagopus), Arctic wolf (Canis lupus), Arctic hare (Lepus arcticus), Arctic weasel (Mustela), snowy owl (Nyctea scandiaca), several species of lemming (a group of rodents that make up part of the subfamily Arvicolinae) and ptarmigan (Lagopus), and a number of species of waterfowl.
Although the number of insect species in the Arctic is small compared with that of temperate regions, those that are present are quite successful. Arctic insects resist freezing winter temperatures. Some groups of species, such as tundra-adapted mosquitoes, possess high concentrations of glycerol, which acts as an “antifreeze” to lower the temperature at which freezing occurs. Many tundra insects and spiders are dark in colour, which absorbs more sunlight and allows these animals to maintain higher body temperatures. Some of the tundra species of black flies and mosquitoes do not require a blood meal before depositing their eggs, in contrast to their temperate-region counterparts.
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Use of sunlight and carbon dioxide
The flora and fauna of Arctic tundras and alpine tundras are affected by differences in day length and in the concentration of carbon dioxide (CO2) in the atmosphere. Plants and animals of alpine tundras are subjected to the same day-night regime as are other organisms at lower elevations in tropical or temperate regions, and numerous activities of these organisms are controlled by the length of the night (see photoperiodism). Over most of the Arctic, on the other hand, light prevails continuously for one to four months, and biological rhythms are induced by variables other than a daily dark period. Many Arctic tundra plants, for instance, flower abundantly only when exposed to continuous or nearly continuous sunlight. In insects, the rhythms of feeding, flight, and swarming, which are normally controlled by light-dark cycles, respond rather to prevailing temperature or sunlight. Birds and large mammals of the Arctic tundra appear to observe a “quiet period” in early morning, though this period is not as pronounced as it is in the animals that inhabit alpine tundras in temperate regions. CO2 levels are lower in alpine tundras because of thinner air at higher altitudes, and alpine plants are more efficient in utilizing these lower levels of CO2 in photosynthesis than are their Arctic counterparts.