FIG. 24-3 Columbia ground squirrel in alpine tundra, Glacier 

 National Park (courtesy R.L. Day). 



Mountains the brown-capped and black rosy finches 

 replace the gray-crowned rosy finch. Rock wrens 

 and horned larks are occasional summer visitors. In 

 the alpine meadows of the far North, savannah spar- 

 rows and upland plovers are common, although 

 they belong principally to the prairie biociation and 

 grassland serai stages of the boreal coniferous forest. 

 Also in the North, around ponds, occur lesser yellow- 

 legs, herring gulls, short-billed gulls, and Bonaparte's 

 gulls (Drury 1953). 



Except for the caribou and pipit, the alpine and 

 arctic tundra biociations have no important species 

 in common. There appears less taxonomic relation to 

 arctic tundra with animals than plants. Probably 

 most of the species listed above are of northern origin 

 and, entering North America over the Bering land 

 bridge, dispersed southward on the mountains as they 

 became elevated and the alpine tundra differentiated. 



Reptiles and amphibians are uncommon. In con- 

 trast to the arctic tundra, flies are comparatively few 

 except in the vicinity of ponds, but there is an abun- 

 dance of springtails, ground-dwelling beetles, leaf- 

 hoppers, grasshoppers, true bugs, butterflies, ants, 

 bumblebees, mites, and spiders (Hay ward 1945, 

 1952). 



Alpine ponds have an impoverished fauna. In a 

 small pond at 3507 m (11,500 ft) in the Colorado 

 Rockies of maximum depth one meter and which 

 freezes solid in the winter, plankton was scant during 

 the summer after the ice melted, but midge fly larvae 

 reached populations of over 1900/m2, Pisidiiim fin- 

 gernail clams, 1470/m-, and tubificid worms, 168/m-. 

 A fairy shrimp was the most characteristic metazoan 

 in the open water, although a small number of aquatic 

 insects occurred along the shoreline (Neldner and 

 Pennak 1955). Phyto- and zooplankton tend gen- 

 erally to be represented by fewer species and a smaller 

 number of individuals than in temperate or tropical 

 lakes (Thomasson 1956). 



Animal adjustments 



As in the arctic tundra, most of the residents 

 in the alpine tundra that remain active over winter 

 are white in color : mountain goat, mountain sheep, 

 Dall's sheep, and white-tailed ptarmigan. 



The pikas inhabit masses of loose rock rather 

 than the climax meadow itself and also occur well 

 below tree-line. During the summer they gather 

 stacks of tundra vegetation and during the winter 

 subsist on this hay. Pocket gophers spend most of 

 their existence in underground burrows feeding on 

 roots and bulbs and hence are well protected from 

 winter cold. The hoary and golden-mantled marmots 

 and ground squirrels hibernate. Wapiti and deer mi- 

 grate to the lower mountain slopes and valleys for 

 the winter as do most of the birds. There is often 

 some downslope movement of mountain sheep and 

 goats for the winter, but it is not so extensive as with 

 the wapiti and deer (Hay ward 1952). The be- 

 havior and interrelations of wolves, Dall's sheep, cari- 

 bou, and other species in the high tundra of Alaska 

 are described in detail by Murie (1944). It is of in- 

 terest that subspecies of mountain sheep formerly 

 occurred regularly on the Great Plains and in desert 

 regions at low altitudes (Buechner 1960). 



Low temperature slows up the development of 

 insects and other invertebrates and reduces the num- 

 ber of generations possible during the year. Animals, 

 however, are generally acclimatized to be active at 

 low temperatures. For example, springtails are 

 sometimes abundant on the snow, where they freeze 

 at night and thaw out during the day. An interesting 

 food-chain occurs with their feeding on conifer pollen 

 falling on the snow and being fed upon by mites. 



Because of the usually strong winds, insects and 

 even birds stay close to the ground and fly as little as 

 possible. Many insects are wingless. Birds commonly 

 feed and build their nests on the sheltered side of ob- 

 stacles, or they crawl into holes and crevices. When 

 in the open, they persistently face the wind (Hingston 

 1925). 



In the Colorado Rockies, grasshoppers are among 

 the most numerous species. However, of 28 species 

 recorded, only 1 1 are truly alpine species, the rest 

 being found only as adults which have flown or been 

 blown up from lower altitudes and do not repro- 

 duce successfully there (Alexander 1951). In Tibet, 

 grasshoppers go as high as 5540 m (18,000 ft) ; bees, 

 moths, and butterflies to 6460 m (21,000 ft) ; and 

 spiders to 6770 m (22,000 ft) (Hingston 1925). 



During the late spring, south slopes on the moun- 

 tains become free of snow before the north slopes 

 because they get direct radiation of the sun. Conse- 

 quently, plant and animal life become active on south 

 slopes before they do on north slopes. Individuals 

 of the same species will also begin growth and repro- 



322 Geographic distribution of communities 



