Amphibian, reptiles and herbivore mammals in the Arctic
Arctic ecosystems are relatively young in terms of geological time, having developed mainly over the past three million years. In general, species richness is lower in the Arctic than in southerly regions, which is consistent with general scientific observations that biodiversity declines from the Equator the poles. The terrestrial Arctic ecosystems are characterised by a short productive summer season and large variety in regional climates: on the Taimyr Peninsula in Siberia only 500 kilometres separate the lush Arctic and the high Arctic ‘desert’. With sharp contrasts in regions the terrestrial species are also challenged by extreme seasonality with ground-level differences in temperature of up to 80° Celsius between the winter minimum and summer maximum temperatures with strong north-south and coastal-inland gradients.
Minimal representation of species in the Arctic
Regarding terrestrial carnivorous mammals there are 13 species found in the Arctic, representing about 10 percent of the 128 species found worldwide. All 13 species are found around the Arctic and inhabit the high Arctic. When it comes to birds, despite its harsh environment, the Arctic is populated by a variety of different bird species. In fact there is roughly 200 species of birds, corresponding to around 2 percent of global avian species diversity. Birds have the ability to make the Arctic home due to strong seasonal bursts of food availability, whether its plant material, invertebrate biomass or zooplankton. This constant supply of food along with relative safety from predators, along with continuous daylight during the summer months means a viable environment for survival.
Amphibian and reptiles in the Arctic
The least represented species in the Arctic are amphibian and reptiles. Globally, amphibian species and reptiles account for nearly 15,000 species, however only five amphibians and one reptile are found in the Arctic. This lack of specie richness is similar to the desert regions of the world. Their lack of presence in the Arctic is due mainly to the fact their body temperatures are determined by ambient conditions. While the first records of Arctic amphibians date back to expeditions in the 19th and early 20th century, scientific knowledge of these species is limited with few studies conducted on their distribution, genetics, development, hibernation patterns and diet. Nonetheless, what is known is that amphibians and reptiles reach the Arctic on its periphery where their overall population numbers are very low.
Scientific studies of amphibians and reptiles
There have only been two main research studies conducted on amphibians and reptiles in the Arctic, both conducted over the past 10 years. One study examined the molecular genetics of the Siberian newt throughout its range and found different genetics amongst the populations, which is speculated to be due to the repeated process of colonisation of new territories during warm inter-glacial periods and subsequent retreats during glacial peaks. It was found the Siberian newt first colonised territories in the Eastern part of Siberia followed by migration towards the Urals before heading east towards Beringin and Kamchatka. Meanwhile, a study in North America on the wood frog found the species migrating northwards towards the Arctic at a rapid pace with expansion towards the north and northwest into Arctic Alaska and most of the sub-Arctic Canada.
The Siberian Newt a popular amphibian in the Arctic
The Siberian newt is of interest at it is considered to be the most widespread amphibian species in the Arctic and sub-Arctic in addition to having the widest geographical range of any recent amphibian species at around 12 million square kilometres. Their northernmost habitats mainly consist of grass undershrubs and lichen moss bogs as well as low shrub-moss and grass-moss tundras. The Siberian newt makes its entrance into the Arctic in the polar Urals and reaches the Arctic Ocean in some areas. The common frog specie also makes its way up to the Arctic in the eastern hemisphere where it crosses into the low Arctic region through he northernmost peninsulas of Norway and along the eastern slope of the Polar Urals. The common lizard too also makes an appearance in the Arctic. Its journey northwards is through the Kanin Peninsula.
Herbivores mammals in the Arctic
Herbivores comprise the majority of Arctic terrestrial mammal species with three main types based on body size found: The small-bodied voles, lemmings and pikas (24 species with body weights ranging from 25 to 250 grams), which are often the most numerous mammals in the tundra ecosystem; medium-bodied herbivores (9 species with body weights ranging between 0.5 to 35 kilograms) including hares, ground squirrels and the American beaver. These species are usually found at lower densities than small mammals but can be more locally abundant depending on the suitability of habitats; and large-bodied herbivores (6 species with body weights ranging from 40 to 600 kilograms) including the caribou and elk.
Variations in herbivore population numbers
The only species with natural distributions in the high Arctic regions are brown lemmings and collared lemmings. Additionally, they are also found in the low Arctic. Pikes and hares are found in regions of the low Arctic. Two species are found in Russia, the northern pika and the Turuchan pika, while one is found in North America. Four species of hares and found in the Arctic, the snowshoe hare, Arctic hare, Alaskan hare and mountain hare. Scientists have conducted experiments to monitor lemming population abundances in trends by using density of winter nests, mark-recapture live trapping or snow trapping. Research has found that on the Taymyr Peninsula of Russia the Siberian brown lemming population has a cyclical pattern with large increases every 3-4 years from the 1960s to 1990s. Collared lemmings, while being less numerous, also have a cyclical population pattern. On Wrangel Island in the North East of Russia the period between the years with peak population densities has increased from five years in the 1970s to almost 8 years in the 1990s and 2000s. Scientists speculate this could be due to snow conditions more conducive to winter reproduction as a result of more frequent winter thaws. In the western part of the Canadian Arctic Archipelago, Nearctic collared and Nearctic brown lemmings also have shown a similar population trend, with both species population numbers increasing every 3-4 years over the 1960s to 1990s. Similar to the findings in Russia, the cyclical period in the Canadian Arctic have increased to five years since the late 1990s. In Greenland, Nearctic collared lemming population abundance is calculated from winter nest counts at Traill Island. Until 2000, the species had a regular population cycle of increasing in density every four years.
Herbivore distribution only partially determined by temperature
In a recent study by scientists from the University of Lapland, the researchers found evidence that patterns of Arctic herbivores are only partially determined by temperature, with interactions with plants and predators more important for population numbers. The study, part of a collaborative research initiative called Herbivory Network involving researchers from 10 countries, collected information on the distribution of 73 species of vertebrate species found in the Arctic including migratory geese, reindeer and caribou, lemmings and free-ranging domestic sheep. Until now, scientists did not know whether diversity of herbivores in the Arctic was due to physical environmental factors including temperature or biotic factors including plant productivity.