Encyclopedia of Islands

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Biology of the Arctic islands

Arctic islands constitute a major part of the arctic land masses. Low temperatures and short summers are strong environmental fi lters that exclude most organisms from living there. Thus, the diversity of most species groups is lower on arctic islands than on the arctic mainland and more southern latitudes. Arctic species exhibit many different adaptations to cope with these harsh environmental  conditions. 

EFFECT OF PAST AND PRESENT CLIMATE ON  PATTERNS OF BIODIVERSITY AND ENDEMISM

Repeated periods of glaciation during the Pleistocene  have strongly infl uenced the biota of arctic islands. During the Last Glacial Maximum (LGM; about 20,000 years ago), major ice caps wiped out most species in the  Canadian Arctic Archipelago (CAA),  Greenland, Novaya Zemlya, Severnaya Zemlya, Franz Josef Land, and Svalbard (Fig. 1). Some ice-free nunataks and uplands existed, however, and it is debated whether some plants and animals survived the periods of glaciation (glacial persistence or glacial survival hypothesis), or became locally extinct and later recolonized from areas outside the main ice caps (tabula rasa hypothesis). Although a few molecular studies have found support for the glacial survival hypothesis, no paleorecords support continuous in situ existence of life within the glaciated islands.

In contrast, the islands and areas around the Bering Strait (Beringian islands such as Novosibirskiye Ostrova, Wrangel, St. Lawrence, and Diomede) remained unglaciated throughout the Pleistocene. The lowered sea levels during glacial periods resulted in a large shelf area connecting present-day islands with the Russian and Alaskan mainland (the Bering land bridge). These altering connections to the mainland, and the Beringian islands remaining unglaciated, have strongly infl uenced both speciation processes and distribution of species on these islands. The number of endemic species is larger on Beringian islands than on other arctic islands and the diversity of vascular plants and springtails on, for example, Wrangel Island is extremely high (Fig. 2).

The current summer temperatures of the warmest month range from 10–12 °C in the arctic shrub tundra zone to 1–3 °C in the arctic polar desert zone. The polar desert and northern Arctic tundra zones are almost exclusively found on arctic islands. Within a geographical region, summer temperature is the environmental variable that best predicts the diversity of species.

For example, the number of vascular plants decreases towards the north in the Canadian Arctic Archipelago and from Novaya Zemlya to Franz Josef Land in Russia. However, some exceptions exist. In bryophytes, species diversity depends more on substrate than on temperature, and thus the difference in species numbers between north and south Greenland is low.

Although the total number of species decreases towards the north or with lower temperatures, the proportion of widespread species increases. Of 115 taxa of vascular plants found in the arctic polar desert zone, 91.3% occur in both North America and Eurasia, and only one species is endemic to a region. Similarly, in the small arthropods known as springtails, the proportion of widespread species is highest in previously glaciated, high arctic islands.

ISLAND GROUPS

Svalbard and Jan Mayen

The Svalbard archipelago is situated from 74° to 81° N and from 10° to 30° E. The land area is 61,000 km2, but about 60% of this is covered by glaciers. The infl uence of the warm North Atlantic Current gives a more oceanic and warmer climate compared to other islands at this latitude. This is also refl ected in the species diversity, which is comparatively high in Svalbard (Table 1).

 

FIGURE 2.  Vascular plant (red bars) and springtail (Collembola, blue bars) diversity on arctic islands. Data compiled from various sources. The bar for total species of vascular plants in Greenland represents 515 species. The bars for springtails have been doubled to visualize them.

Svalbard was almost entirely glaciated during the last glacial maximum, and paleorecords show a sparse arctic vegetation subsequent to 10,000 years ago. Although this is one of the most remote arctic archipelagoes, molecular analyses of plant species show that it was repeatedly colonized during the Holocene from several source areas (Fig. 3). The main source areas were in northern  Russia/Siberia and northeastern Greenland, areas connected to Svalbard by winter sea ice. Thus, sea ice, probably in combination with wind, might be an important dispersal mechanism to arctic islands. Exceptionally warm winds may also carry insects directly from areas such as Russia to Svalbard, as was observed for the nonresident migratory diamondback moth Plutella xylostella. The few endemic species or subspecies in Svalbard (i.e., the Svalbard reindeer, the Svalbard aphid, and four plant species) have probably evolved recently from species that immigrated after the LGM.

In contrast to most arctic islands, there are no rodents on the archipelago (except the locally introduced sibling vole). The main herbivores are geese and reindeer. The arctic fox feeds mainly on eggs and chicks of sea birds and geese, as well as carcasses of seals and reindeer. There are many seabirds breeding in the archipelago, and these contribute a signifi cant input of nutrients for plant growth.

The only resident bird is the Svalbard ptarmigan (Lagopus mutus hyperboreus), which is endemic to Svalbard and Franz Josef Land.

 

FIGURE 3  Source regions for past colonization of (A) dwarf birch (Betula nana), (B) mountain avens (Dryas octopetala), (C) white arctic bell-heather (Cassiope tetragona), and (D) bog bilberry (Vaccinium uliginosum) to Svalbard. Source regions are inferred from genetic data (amplifi ed fragment length polymorphism). Colors represent main genetic groups, and symbols represent sub-groups. Numbers on the arrows are percentages assumed to have arrived from the source region. The geographic distribution of the species is shaded. 

Jan Mayen is a small (373 km2) volcanic island east of Greenland. It has an extremely oceanic climate with mild winters and relatively cold and wet summers. About twothirds of the 66 vascular plant species found there are circumpolar, whereas the other third is amphi-Atlantic. The only endemic species found are apomictic dandelions (Taraxacum). The arctic fox is the only terrestrial mammal on the island. Large seabird colonies are found during the summer, but only the fulmar (Fulmarus glacialis) stays during winter.

Greenland

Greenland is the world’s largest island. Including the numerous smaller islands along the shore, its total size is 2.17 million km2. The majority of species are confi ned to the ice-free margins, which cover only approximately 410,000 km2. Greenland stretches from 59°45′ N to almost 84° N and spans a vegetation gradient from birch forest in the south to polar desert in the north (Fig. 4).

Considering the large size of Greenland, species diversity is relatively low, and it decreases from south to north as, for example, in vascular plants. Also, there are only a limited number of species that are endemic to Greenland.

Of the total 515 vascular plant species, 32 taxa are endemic. However, 15 of the endemics belong to the apomictic hawkweed genus (Hieracium), which rapidly evolves new species. Endemic species of algae and three spider species have also been recorded, and a few bird subspecies breed only in Greenland, but they overwinter elsewhere.

The relatively low diversity and endemism found in this large island are probably due to its glacial history. Ice-free areas existed in Greenland throughout the glacial period, but according to climate data derived from ice cores, it was so cold during the LGM that only the most cold-adapted species could have survived there. Thus, it is assumed that the majority of species colonized Greenland during the last 11,500 years. This view is supported by molecular studies of several plant species. A large proportion of Greenland’s plants and animals are also found in northwestern Europe, indicating that they arrived from there. Although this distance is long, the Faroe Islands and Iceland form steppingstones along the route. Further, the majority of Greenlandic birds migrate from Europe and could have transported seeds, spores, and even some invertebrates. The majority of spiders and some groups of insects are Nearctic, indicating a high proportion of immigration also from northeastern Canada.

Canadian Arctic Archipelago

The Canadian Arctic Archipelago (CAA) covers an immense area, ∼1.42 million km2, and comprises numerous large and many more smaller islands. It extends about 3000 km from below the Arctic Circle to the northern tip of Ellesmere, and 3000 km east-west from Baffi n to Banks Islands. Ice caps occur in the mountainous northern and eastern parts on Axel Heiberg, Ellesmere, Devon, and Baffi n Islands (maximum elevation 2615 m), but overall, glaciers cover only about 11% of the archipelago. Thus, the ice-free area of CAA is three times as large as the ice-free area of Greenland and more than 50 times as large as the ice-free area in Svalbard.

Recolonization after the LGM occurred primarily from mainland areas to the south, a distance as short as 1–20 km at several locations. Unglaciated Beringia was

also an important source area for many groups, contributing to east-west differences in species composition (e.g., higher diversity of legumes on Banks and Victoria Islands). Glacial refugia on Banks Island provided additional source areas, while postulated refugia on Ellesmere and other islands have yet to be confi rmed.

Considering its large land area, species diversity is low on the Canadian Arctic Archipelago. The strong south-to-north decrease in diversity is correlated with summer temperature and distance from the mainland. However, topography and oceanic infl uences modify this gradient, creating a more complex pattern. Rain shadow effects are responsible for warmer drier summers and the relatively high diversity of the “polar oases” of the Forsheim  Peninsula and Lake Hazen area on Ellesmere Island. Cool summers with extensive cloud and fog are responsible for the low vascular plant and arthropod diversity on Ellef Ringnes and nearby islands. Located north of the “shrub line,” this barren region lacks woody plants, which are so characteristic of tundra vegetation (e.g., willows, mountain avens, Ericaceae).

No endemic vascular plants, bryophytes, lichens, mammals, or arthropods are known from the CAA, but several species are confi ned to the Archipelago and Greenland, such as Peary caribou, the alkali grass Puccinellia bruggemannii, the moth Gynaephora groenlandica, and the wolf spider Alopecosa exasperans. Also, at least one undescribed species of spider has been found on Banks Island.

Russian and Beringian Islands

The Russian arctic islands can be divided into fi ve main groups: (1) Novaya Zemlya (“New Land”) with adjacent Vaigach, Kolguyev, and some smaller islands; (2) Franz Josef Land; (3) Severnaya Zemlya (“North Land”); (4) Novosibroskiye Ostrova (“New Siberian Islands”); and (5) Wrangel and Gerald Islands. Besides these main groups there many small islands at the Ob’, Yenisei, Kheta, Lena, and Kolyma deltas and near Taimyr Peninsula. In addition, there are several arctic islands belonging to Russia and the United States in the Bering Strait and Bering Sea (e.g., St. Lawrence, Yttygran, Arakamchechen, Diomede and King Island).

The most biologically diverse and well studied island in the Russian Arctic is Wrangel Island. It is a remote, relatively small island of about 7,600 km2, with the highest elevation above 1000 m. A unique feature of this island is the very limited extent of Pleistocene glaciations combined with the lowered sea level during LGM, making Wrangel a part of the Bering land bridge. This has enabled enrichment of the fauna and fl ora by very different elements originating in boreal, forest-tundra, tundra, arctic polar desert, and even steppe zones from Asia as well as North America, which has resulted in a species composition on Wrangel Island different from those on all other islands. For vascular plants, 417 species are known, more than for the whole CAA (349 species) and the northwest sector of the Siberian arctic (387 species), and approaching that of Taimyr Peninsula (494) and Greenland (515).

Similarly, the diversity of spiders, beetles, and birds is high on Wrangel Island compared to Svalbard and Greenland. The diversity of many insect families and orders is higher than on any other arctic island, including Greenland.

The recurrent connections and disconnections of Wrangel Island also led to speciation in mammals, vascular plants, and some groups of arthropods. The number of endemic species on the island is extraordinarily high for the Arctic in general and for arctic islands particularly.

There are 23 endemic vascular plant species, four spider species, 20% of weevils, both of the rodents Dicrostonyx groenlandicus vinogradovi and Lemmus sibiricus portenkoi (Fig. 5), and at least one bird subspecies Cepphus grylli tajani. If the recently (3500 years old) extinct dwarf mammoth is counted, the level of endemism of mammals would be higher. In the late Pleistocene several other ungulates such as Przewalski’s horse, woolly rhinoceros, primeval bison (Bison priscus), musk ox, woolly mammoth, and reindeer occurred on the island.

The Novosibroskiye Ostrova (New Siberian Islands) consists of two larger groups of islands, Lyakhovsky and Anzhu, and one small group called De-Longa. With its area of about 36,000 km2, this region is about fi ve times larger than Wrangel Island, and like Wrangel, it was also unglaciated and connected by the Bering land bridge.

However, the archipelago is rather fl at, which limits habitat diversity, and the diversity of plants, springtails, birds, and beetles is less than on Wrangel. There are some species on Novosibroskiye Ostrova that do not occur on Wrangel, including a willow grouse species and two goose species. The mammal fauna consist of wolf, wild reindeer, one lemming species, and arctic fox. The fossil mammoth fauna is even richer than on Wrangel Island with additional species such as saiga antelope, cave lion, and voles. Also, the fossil beetle fauna is much richer  (about 100 species during the past 200,000 years, or 58 species during last 115,000 years) than the present beetle fauna (about 10 species). In the nineteenth and beginning of the twentieth centuries, digging up and selling ivory from fossil mammoths was a profi table business.

The Severnaya Zemlya Ostrova consist of four large  (October Revolution, Bolshevik, Komsomolets, Pioneer) and about 70 smaller islands, covering a total area of about 37,000 km2. Although the island group remained partly unglaciated throughout the Pleistocene, it was not connected by the Bering land bridge, and it is also situated rather far north.

Thus, species diversity is lower than on most other Russian archipelagoes with, for example, about 78 species of vascular plants. Only 17 of the 32 bird species that have been observed on the islands breed there.

Six terrestrial mammals are known there: lemming, arctic fox, wolf, ermine, arctic hare, and reindeer. Four species of beetles have been found on the archipelago, but only on the southernmost island.

The Novaya Zemlya Archipelago consists of two large and several smaller islands, in total about 81,000 km2. The number of vascular plants and springtails is similar to that on many other islands that have been previously glaciated. The fl ora represents a transition between the arctic Europe and Asia but with a separate mountain range element connected to the Urals. Some endemic vascular plants in Novaya Zemlya have been proposed, but they are dubious. There are two lemming species, a local reindeer subspecies, and arctic fox on the archipelago.

Franz Josef Land (16,100 km2) is the northernmost archipelago and consists of almost 200 islands. Glaciers cover 85% of the archipelago. It is the most species-poor arctic archipelago, with only about 50 vascular plant species, about 150 bryophytes, over 300 lichens, one terrestrial mammal (arctic fox), at least 14 springtails, two spiders, and no beetles. Only 14 bird species breed on the island, but almost 30 other bird species have been observed visiting.

Aleutian Islands

The Aleutian and Commander Islands are a 2,100-km long archipelago to the south of the Arctic, separating the Bering Sea from the North Pacifi c Ocean. Although the U.S. government includes this archipelago in its defi nition of the Arctic because of the treeless landscape that prevails here, this is caused largely by strong winds rather than low temperatures and short growing season, as is the case in the Arctic. These islands serve as a natural bridge between Old World and New World fl ora and fauna, although physical evidence suggests that this archipelago was under ice during the LGM, so terrestrial species on these islands should be recent colonists (i.e., since the last glaciation, or less than 10,000 years ago). However, the relatively high levels of endemism (for high-latitude organisms) that characterize the Aleutian and Commander Islands suggests that many of these taxa were isolated for longer periods of time, probably in “cryptic” glacial refugia: ice-free areas that harbored multiple taxa through the Quaternary glacial cycles, though so far only evident through the biological record.

Moreover, natural selection has resulted in local adaptations to the harsh conditions of the islands, with evidence of traits such as increased body size in some bird species. In the same way, the Alexander archipelago, a chain of over 1000 islands off the southeastern coast of Alaska that is also recently glaciated, though currently covered by evergreen forest and even temperate rain forest, is characterized by a number of monophyletic lineages, which may be attributed to multiple Holocene invasions or the persistence of taxa in refugia during Pleistocene glacial advances.

CHARACTERISTICS OF SPECIES

Plants

The arctic fl ora ranges from shrub tundra in the south to almost barren polar desert, where no woody plants live and only scattered herbs, bryophytes, and lichens are found. The majority of species are long-lived perennials with relatively low resource allocation to sexual reproduction and high reliance on asexual reproduction for population maintenance, but a high variety of life strategies exists.

There are fewer pollinators and lower pollinator activity in the Arctic than in other regions. Plant species adapted for wind pollination are dominant, and self- pollination is common. The growth forms are often prostrate mats, tussocks, rosettes, or cushions, which reduce desiccation and mechanical damage from the strong wind and maximize heat absorption (Fig. 6). In addition to the low temperatures and short growing season, drought places a very signifi cant stress on plant life. The majority of bryophytes and lichen species are well adapted to periods of drought and increase both in abundance and ecosystem importance northwards.

Invertebrates

Invertebrate groups occurring on arctic islands have evolved from species in the boreal biome, where winter temperatures are often lower than in the tundra zone, and they have similar adaptations to cold resistance as boreal species. The main limiting factor for invertebrates is heat defi cit in the short (2–3 month), cool growing season, and therefore the main adaptations are directed towards shortening of the life cycle (vivipary, reduction of size) or extension of the life cycle to several years. They survive the winter by producing cryoprotectors, being able to dehydrate, or overwintering as cold-resistant eggs.

In addition, behavioral strategies may assist in avoiding low-temperature extremes, for example seeking protected places to avoid winter cold, such as under thick snow cover or close to non freezing water currents.

In arthropods, adaptations to the arctic climate lead to dominance by small-sized groups such as mites, spiders,  and springtails, which have relatively high species diversity on arctic islands. Large sized insects, such as large ground beetles and bumblebees, are lacking on most arctic islands, whereas beetles and some other megadiverse groups, such as moths and true bugs, are represented on arctic islands by fewer species than small-sized groups. 

There is a decrease in species numbers of herbivorous insects (especially among beetles, butterfl ies, moths, and true bugs) in comparison to predaceous ones.

Mammals and Birds

To survive the harsh winter of the Arctic, mammals and birds have developed morphological, physiological, and behavioral adaptations. The difference between ambient temperature and body temperature may be as high as 90 °C. Larger arctic animals have developed thicker and denser fur or plumage or a thick fat/blubber layer to keep warm without spending much energy. Smaller animals such as lemmings and voles live mainly under the snow, which acts as a thick insulating layer. Ptarmigans stay in “dock” (under snow) during bad weather conditions to reduce heat loss. The blood circulation system is also adapted to minimize heat loss by countercurrent heat exchange and by slowing down the circulation to extremities. Many arctic mammals have enlarged nasal cavities, and circulatory adjustments in the nose reduce water and heat loss. Some arctic animals, such as the Svalbard reindeer and ptarmigan, store large amounts of fat during the summer and autumn season, which is used to survive the winter. Most arctic birds species migrate south before the winter period. When they arrive is closely linked to the timing of breeding relative to snow melt and peak food production.

HUMANS ON ARCTIC ISLANDS

Humans have long been a part of the arctic environment, intimately connected to the local resources on land and sea. The indigenous peoples harvest natural resources both from the terrestrial (arctic fox, ptarmigan, reindeer, caribou, musk ox) and the marine environment (fi sh, whale, seal, polar bear). In Greenland, fi shing is the all-dominating trade and accounts for 95% of total exports, but in the hunting districts of the outlying areas the seal and whale catch is of great importance and forms a stable existence for one-fi fth of the Greenlandic population. Reindeer herding is of local importance only on few arctic islands, such as in northernmost Norway.

The 15 communities in the CAA are mainly inhabited by Inuit. Most Russian arctic islands are not inhabited except by the staff of small military camps, nature reserve stations and weather stations, but indigenous people live on some islands; for example, some Nenet families live on Novaya Zemlya. Fifty-seven thousand people, predominantly Inuit, live in towns and small settlements on Greenland. In Svalbard there is one Norwegian settlement with around 2000 inhabitants and one Russian settlement with about 500 inhabitants. Industrial activity is found only on a few arctic islands, such as mining activities in Svalbard, on Kolguyev, and, until recently, on Little Cornwallis and Baffi n Island. There are huge reserves of oil and gas on arctic islands and the surrounding seafl oor, such as the Sverdrup Basin in the Canadian high arctic, and exploration drilling is done in several locations.

Tourism and research activities are increasing on some arctic islands such as Svalbard and Baffin.

CONSERVATION OF ARCTIC FLORA AND FAUNA

The arctic fl ora and vegetation are vulnerable to physical disturbance, and vehicle tracks often last for decades.

Humans have overexploited many species, such as whales, polar bear, and arctic fox. Although some species and populations have recovered, others are still threatened. Long-range pollution from the industrial part of the world, such as heavy metals, persistent organic pollutants (POPs), and radionuclides, has reached arctic islands, and such pollutants are accumulating in some organisms. Climate change is predicted to be of higher magnitude in the Arctic than in other places in the word. Because the arctic islands represent the “end of land,” high arctic species have no further place to migrate if they are outcompeted by more southern species, and they may thus become extinct. Global warming will also open up the northern sea routes both in Canada and Russia and make the arctic oil and gas reserves more accessible, which would potentially lead to increased pollution and disturbance.

Knowledge necessary for conservation is lacking for many islands, species, and ecological processes in the Arctic. For example, the identifi cation and classifi cation of arctic invertebrates, fungi, bryophytes, and microorganisms is limited. Although some monitoring programs exist, information on the status and trends of arctic populations is fragmentary. For proper management in a changing climate, more knowledge is needed about the species found on arctic islands, the ways they interact, and how they respond to the changing physical environment, especially climate.