Mountain Wildlife - Mountain Geography: Physical and Human Dimensions - page 409

tain building, while the Pleistocene—the last 2 million years—was a period of major cli-
matic fluctuation. Although mountain building during the Tertiary was the initial event,
and life had to adapt to the changing conditions of increasing altitude and relief with
uplift, the Pleistocene has been by far the most important in terms of the present dis-
tribution of life in mountains. During the Ice Ages, the northern hemisphere was most
affected because of its larger land masses and resulting continental climate; mountains
served as centers of increased snow and ice accumulation, and huge lowland ice sheets
extended from the north into the middle latitudes. Vast amounts of bedrock were re-
moved, and the rock was ground into dust and redistributed by water (silt) and wind
(loess).
While the centers of oceans and glaciers contain little life, the edges of oceans (in-
tertidal zone) and of glaciers (periglacial environment) can be productive, pulse-sta-
bilized ecosystems. Glaciers annually produce pulses of fertile rock dust and meltwa-
ter. These initially discharge into broad, braided streams that fill the ever-rising valley
bottoms with glacial debris and silt. When flood waters recede, the fertile silt is dried
and blown away to be massively deposited as fertilizing loess. The effects of fertility
and water are enhanced plant productivity, which in turn attracts a diversity of wild-
life, including thriving populations of large herbivores and carnivores. Moreover, there
can be “land islands” protruding from oceans and from glaciers (the latter are called
nunataks ). These mountains may be vegetated and home to large herbivores and carni-
vores. Glaciers may have so much debris in and on the ice that even forests of spruce,
poplars, willows, and birch may grow on the ice. On the Klutlan glacier of the western
Yukon Territory, Canada, moose populations winter in such willow and dwarf birch flats,
which are also visited in summer by caribou, mountain sheep and goats, grizzly bears,
and wolves, while willow ptarmigan nest in bogs on the glacial ice.
The evidence of the most recent Ice Age (Wisconsin) is still relatively fresh, and
the pattern of glacial development can be more readily reconstructed. Although the
lowland ice retreated 10,000-15,000 years ago, mountain glaciers melted more slowly;
the largest present-day glaciers may be remnants of the Pleistocene ice. Most small
mountain glaciers, however, have melted entirely. Numerous small advances and re-
treats have occurred within the last 10,000 years, greatly affecting the fate of civiliza-
tions—studies have shown a slow rate of soil and vegetation development in some areas
abandoned by these retreating glaciers. Some of the first animal inhabitants are primit-
ive species of springtails and mites, followed by arthropods such as beetles and spiders.
Most early insect occupants are carnivores (Brinck 1966, 1974) that live on algae, lar-
vae, and other insects. Eventually, as the ecosystem develops, the various components
and niches are filled with a variety of life forms, but on bare rock at high elevation, it
can be a slow process.
Clearly, the age of the surface is a major factor in ecosystem development. This is
demonstrated on a macro scale by the great floral and faunal richness of the Central
Asian highlands (Sushkin 1925; Meinertzhagen 1928; Swan and Leviton 1962; Zimina
and Panfilov 1978). This area escaped extensive glaciation during the Pleistocene owing
to its aridity, so it served as a refugium for numerous species. In fact, it is believed that
many present arctic and alpine species originated here and later spread to the Arctic
and the mountains of Europe and North America (Hoffmann and Taber 1967; Hoffmann
1974).