Interaction Between the Living and Non-Living Environment
Each animal in the region utilizes its own vegetative habitat niche which provides food for some animal species and shelter for others. Many physical features of the habitat combine to make each vegetative community uniquely habitable for its associated fauna. Dall sheep, for example, live in alpine tundra almost exclusively. Moose, wolves, wolverines, weasels, and bears, on the other hand, are more adaptable and use a number of habitats during their annual cycle of activities, but even these animals often show seasonal preferences. Moose, which may range widely over open tundra in spring, summer, and fall, generally seek timber or high brush habitats in winter where cover and food are available, usually in stream bottoms. Bears change their habitats to correspond with where and when food supplies are plentiful—roots and ground squirrels in spring, berries in season, and various fish spawning runs. Wolves, weasels, and wolverines show less preference for specific habitats.
Animals modify their own habitats as well as creating and modifying habitats for others. For example, caribou grazing habitats may favor one group of plants over another, and caribou feces and carcasses fertilize the soil and enhance plant growth. They may also damage large expanses of their range, which may take as long as 50 years to recover its full capacity. As a result, animals that depended on the original vegetation may disappear, while those requiring the new type may replace them. Some animals may themselves be a habitat for others. Wolves, for example, are commonly infested with numerous endo- and ectoparasites and used as habitat for part of their life cycle. Figure 130 reflects the interrelationship between plants and animals.
Many insects are conspicuous during summer. Other invertebrates, mainly mature insects and mites, are even more numerous beneath the surface of the soil. Mosquitoes, both airborne adults and aquatic larvae, live throughout the region in summer. Mites (Arachnida) and springtails (Collembola) are dominant invertebrates within the soil.
Moose use a variety of habitats from bottomland timber to alpine tundra.
Red foxes range widely throughout the region.
A fairly diverse mammalian fauna inhabits northwest Alaska. The distribution of terrestrial mammals is largely determined by habitat type, which ranges from tundra to various forest types. In more northern latitudes caribou are the most conspicuous mammal (Figure 131), and their abundance draws wolves to the tundra in search of food. Although wolves also prey on other animals, caribou are their principal quarry.
In moist habitats Arctic and red foxes are numerous, particularly during periods when small mammal populations are high. Lemmings and voles, both cyclical in abundance, feed on the grasses of the moist tundra and use them for insulating their nests. Muskoxen also occur on coastal moist tundra. These mammals cannot feed in deep snow, so they require areas which are swept free of snow by the wind.
In higher, drier alpine communities of the Seward Peninsula, wolves, grizzly bears, red foxes, ground squirrels, and hoary marmots den in the dry soils of the tundra. Grizzly bears often tear up large sections of sod looking for ground squirrels in their dens. Dall sheep occur in alpine tundra where they feed on bunchgrass (Dryas) and lichens in terrain where their climbing ability gives them an advantage over potential predators. Like the muskoxen, Dall sheep avoid deep snow, and in winter they often head for the higher ridges that are blown clear.
The varied terrestrial habitats of the region support abundant bird life; a total of 120 terrestrial and aquatic species have been recorded at Cape Thompson (Williamson et al. 1966). The many Asiatic species that frequent the area make it particularly interesting to ornithologists. A number of surveys have been made of habitats in the region.
Many species vary in their adherence to specific habitat types, particularly those that are considered essentially aquatic. Many that appear on the list of aquatic birds, such as swans, geese, pintail duck, most shorebirds, and cranes, nest and feed in wet and moist tundra. Such birds as robins, chickadees, and woodpeckers are confined to wooded habitats for nearly all their activities, and the golden eagle, water pipit, and gray-crowned rosy finch are typically alpine. The raven is perhaps the most cosmopolitan species and may be found almost anywhere in the region.
|The semipalmated sandpiper is one of the earliest spring arrivals on the wet tundra.|
Birds of prey, particularly the rough-legged hawk, golden eagle, peregrine falcon, and gyrfalcon, are conspicuous in the region. Most of the peregrines in the Northwest Region are endangered American peregrines (Falco peregrinus anatum), which migrate to the southern United States and Mexico where they feed on prey contaminated with DDT that reduces breeding success. It is on the endangered species list of the U.S. Fish and Wildlife Service and receives special protection under the Endangered Species Act. The Eskimo curlew (Numenius borealis) has not been recorded for a number of years and may be extinct. It was formerly found in its greatest abundance in the Kotzebue Sound area.
The most abundant terrestrial birds in the region in terms of both number of species and number of individuals are the passerines, or perching birds. They range from warblers and redpolls to ravens and occupy various habitats from open tundra to forest. Species that have spectacular migrations include the wheatear, which leaves its nesting grounds in the region, traverses the Bering Strait, and then travels southwest across Asia to winter in central Africa, and the Arctic warbler, bluethroat, yellow wagtail, and the white wagtail, which nest within the region and winter from Borneo west through India and Africa. Most of the three species of swallows migrate to central South America.
All of these species as well as aquatic birds are an essential part of the natural system. Some hawks and owls may feed on other birds or their eggs. Snowy owls, eagles, gyrfalcons, roughlegged hawks, and others feed on small mammals or fish. Most of the smaller passerines feed on plant seeds or insects and other invertebrates and are themselves a source of food for other birds and carnivorous mammals. Ptarmigan, snowy owls, and others are eaten by man, and all birds add to man's enjoyment of the landscape.
Invertebrates are often not considered in the terrestrial fauna of a region. One attack by a swarm of mosquitoes or such other evidence of their activity as fly-blown meat or damaged vegetation, dramatizes their presence in this environment. Flatworms, roundworms, insects, and mites are the most common invertebrates and a square meter of the active layer of the soil (top 10 cm) may contain many thousands. Douce (1973) found 37 species of mites that totaled more than 25,000 individuals per square meter of arctic soils. Challet and Bohnsack (1968) found the primitive springtail to be even more abundant than mites in wet soils. The most prevalent visible insects are mosquitoes (Culicidae) and midges (Chironomidae). Spiders are also important predators of smaller invertebrates. Weber (1950) mentions how botflies (Oedamagena tarandi) harass caribou and ruin their hides for human use.
Although insects have not been studied much in arctic Alaska, the basic life histories of several species of mosquitoes (family Culicidae) have been worked out. None are known to transmit diseases, but their impact is obvious to anyone who has been on arctric tundra or in subarctic forest in early July of a "bad" mosquito year. People vary in their sensitivity to mosquito bites. Some are little affected and others only moderately so, but some individuals become so sensitized that a few bites may make them seriously ill. Except for extremely sensitive people, effective protection can be provided from their attacks by repellents, headnets, lightly woven clothing, and insect-proof shelters.
[Alaska Regional Profiles, Northwest Region, pp. 143-149]