3.2.1 Life on land at high latitudes
Relatively few species of terrestrial organisms live permanently at high latitudes. For example, although the land area of Svalbard is about 62 000 km2, almost half that of England, there are only a few hundred species of insects and other invertebrates, two resident terrestrial mammals, the arctic fox (Figure 17a) and reindeer (Figure 17b), one bird (an endemic species of ptarmigan) and no reptiles, amphibians or completely freshwater fish.
However, many other species spend part of the year on or near the land, often while breeding or moulting: seasonal visitors include more than 30 species of migratory birds (various kinds of geese, auks, puffins, skuas, terns, gulls, and eider ducks and snow buntings), and mammals that feed in the sea, such as polar bears, walruses and several species of seal. The simple ecosystem on land and the severe, erratic climate tend to produce ‘cycles’ of population abundance followed by mass mortality or migration (e.g. lemmings in Scandinavia and Russia). Interesting physiological and behavioural adaptations to these fluctuations in food supply have evolved in some of the larger animals. The vast continent of Antarctica has no indigenous terrestrial vertebrates, although many birds, including penguins, skuas, terns and gulls, and six species of seal spend time on or near land.
Only two species of terrestrial mammal occur naturally throughout the year on Svalbard (although a few others have been introduced by humans during the past century). Figure 17a shows the arctic fox (Alopex lagopus), which also occurs throughout the Arctic, and in mountains at lower latitudes. The picture in Figure 17a, taken in late autumn, shows an adult in its long, dense winter coat. The summer coat is usually greyish brown, often with white markings. Alopex is bred in captivity for its fur, which can vary in colour from grey to bluish in winter, and chocolate brown to fawn in summer, hence the common names, silver fox or blue fox. Figure 17b shows a subspecies of reindeer (Rangifer tarandus platyrhynchus) that is endemic to Svalbard. This picture was taken in July, when the vegetation is at its highest, and this young male is growing antlers for the mating season in September.
The situation in the polar seas is very different, which you will discover as you conclude your study of extreme ecosystems by learning about life in the polar seas.