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With its unforgiving and extreme conditions, Antarctica represents a region where life approaches its environmental limits. Terrestrial life must survive in the few, isolated pockets not continually covered by ice and snow. The McMurdo Dry Valleys of southern Victoria Land are of particular interest. There, scientists find extremely basic ecosystems with organisms showing remarkable adaptations.
- Surprisingly enough, Antarctica is home to at least 200 species of lichens, over 100 species of mosses and liverworts, more than 30 species of macrofungi, two species of flowering plants and many species of algae.
- The relationships between these plants and those on the surrounding continents have interested botanists for almost 150 years, and it is only now, after a great deal of specimen-collecting and detailed taxonomic study, that the relationships are finally becoming clear.
All aspects of life are studied, from the bacterial organisms living on sandstone outcroppings to microscopic worms, called nematodes, that live in the gravelly, dry soil.
The Dry Valleys, unlike most other ecosystems, are dominated by microorganisms, mosses, lichens, and relatively few groups of invertebrates; higher forms of life are virtually non-existent. Organisms have, over eons of evolution, developed mechanisms to survive under conditions of desiccation, extreme cold temperatures and with limited food or light for photosynthesis. These organisms are unique and only exist in the frozen Antarctic continent.
All ecosystems are dependent upon liquid water and shaped to varying degrees by climate and material transport, but nowhere is this more apparent than in the McMurdo Dry Valleys. In very few places on this planet are there environments where minor changes in climate so dramatically affect the capabilities of organisms to grow and reproduce.
Biological studies in the dry valleys have revealed life forms that have colonized rocks, soils, glaciers, glacial meltwater streams, and lakes. Bacteria, fungi, algae, mosses protozoa, tardigrades, rotifers, and nematode worms are the most common types of organisms encountered. Algae and lichens are found growing inside sandstone rocks, in which these endolithic microorganisms are living in a relatively stable environment with high humidity and protected from the rigors of the external world. Lichens are found on rock surfaces, from the valley floors to the summits of some mountains. The dry-valley soils, once thought sterile, contain numerous bacteria, fungi, and algae. In damper soils along meltwater streams, mosses are found. Small holes and ponds on the surface of glaciers also provide a habitat for algae and other organisms transported by wind.
The only plants that are relatively "luxuriant" in Antarctica are found in the northernmost parts of the Antarctic Peninsula and some sub-Antarctic islands. They include mosses lichens grasses liverworts, and a few ferns. The animals native to Antarctica include a few species of ducks, a pipet, flies, midges, moths, beetles, and earthworms, nearly all of these occurring on the Antarctic Peninsula and certain islands. Also found are microscopic protozoa, rotifers, and tardigrades, which inhabit moist soils and mosses.
- You'll have to look hard to find any insects in Antarctica, but you might see a springtail jumping among vegetation or find a group of tiny mites under a stone.
- Despite their size, these insects, and the slightly larger ones on the sub-Antarctic islands, are the subject of much research by US, British, French, Italian and South African scientists.
- Many are able to make antifreezes which allow them to survive temperatures as low as -28 °C.
- When frozen into ice, some can put their metabolism into a special state to survive the lack of oxygen.
- They also show a remarkable ability to survive drying out without long-term damage to their cells.
- The lack of species diversity makes these invertebrate communities among the simplest anywhere, so they provide ideal models for understanding how ecosystems work.
- One of the most unusual plant habitats on Earth is in Antarctica: in areas formed from large-grained sandstone, most obviously in Victoria Land, the outer skin of the rocks themselves has been colonized by plants.
- These plants live within the rock, growing between the sand grains and forming separate layers of algae, fungus and lichen.
- Just enough light penetrates the rock for photosynthesis to occur for a short period each year when melt water is available.
- Acids excreted by the plants eventually dissolve the rock and the outer skin breaks off, leaving an obvious dark mark where the algal cells remain.
- The growth rate of these plants is so slow that some may well be many thousands of years old.
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