The Arctic and Its Wildlife© 1986 BRYAN SAGE Facts on File excerpts from pages 118, 121-22, 173-74 |
Some Aspects of Distribution
According to Guthrie (1968), the number of small mammal species present in the
tundra seems to have increased considerably since the glaciations of the late
Pleistocene, primarily by immigration from more southern locations, while the
number of large mammals has declined.
It can be seen that four groups of small mammals (shrews, hares, sciurid rodents
and microtene rodents) occur regularly in Arctic tundra, although their distribution
does not always correspond entirely to the distribution of that habitat. Some of
the species are tundra-specific and, according to Hoffman and Taber (1968), evolved
in central Eurasia during the early pleistocene and migrated to North America.
Population Cycles
Long-term mammalian population cycles have been proposed for several parts of the
world, but in the Arctic and Subarctic two cycles stand out partcularly clearly:
the Snowshoe Hare and the Lynx cycle with a periodicity of about ten years in the
boreal forest of the New World, and 4-year cycles for several species of voles and
lemmings in the tundra zone around the world (and in some grasslands in lower
lattitudes). The best known 3-4 year cycles is that of the Brown Lemming. Detailed
discussion of population cycles will be found in Batzli et al (1980), Finerty (1980),
Remmert (1980), Southern (1979) and Stoddart (1979). It should be noted that the
interval between successive peaks may vary within small limits, and that the
regularity of the cycles refers only to the intervals between peaks. The individual
peaks may not, of course, necessarily be of the same amplitude. The cycles are
typically assymetrical, with populations declining at a greater rate than they
increase. As stated by Crawley (1983), there is strong evidence that herbivore
population cycles are caused by plant-herbivore interactions (rather than by
predator-prey, disease-host, or plant-enivornment interactions).
