Mountain Wildlife - Mountain Geography: Physical and Human Dimensions - page 429

longer) and the reduced number of reproductive cycles efficiently control the popula-
tion levels, in keeping with the ability of the environment to support them. It should be
mentioned, however, that the growth rates of yellow-bellied marmots at high altitudes
in the Colorado Rockies are faster than those at lower altitudes (Andersen et al. 1976).
The degree of sociability may be more a function of the extent and density of satisfact-
ory hibernating sites than of environmental severity.
FIGURE 8.11 Correlation among length of growing season, age of dispersal, and sexual maturity in
three species of marmots in different environments. Protruding vertical lines at the top represent
years from January to January. The woodchuck, living in an area with a long growing season, dis-
perses and breeds at the end of the first year, whereas the Olympic marmot, living under harsher
conditions with a very short growing season, waits two years to disperse and another year before
breeding. (After Barash 1974: 418)
As with the larger animals, insects at higher altitudes increasingly limit their activ-
ities to the daytime hours. Those species that are predominantly nocturnal in lowlands
(e.g., moths) become less common at higher altitudes, and those that do persist often al-
ter their habits, becoming active during the day rather than at night (Mani 1962). Feed-
ing is limited to brief periods in early morning and late afternoon, perhaps only two or
three hours daily. They spend much of the rest of the time hidden under rocks and veget-
ation (but see Schmoller 1971). The proportion of plant-eating species decreases above
the timberline (as might be expected, since plants also decrease) until near the snow-
line predators dominate, living on other insects or organic material transported upward
by rising air currents. In the eolian zone, utilization of the snow as a storehouse for food
becomes an increasingly important part of adaptation for life (Swan 1961, 1967; Mani
1962; Papp 1978; Spalding 1979).
Reproduction in insects is synchronized to match environmental conditions. They de-
velop very rapidly within the brief growing season, and the velocity of development in-
creases through the summer, so that later stages in the life cycle are more accelerated