Terrestrial ecosystems in the Antarctic

The composition of the terrestrial Antarctic flora and fauna and the distribution patterns of a number of species and of the principal vegetation types is now reasonably well established, at least in outline, for the Antarctic Peninsula region and the areas about McMurdo Sound as well as for some areas around the coastal ranges of East Antarctica. Detailed research at Signy Island has provided information concerning the biomass and productivity of certain vegetation types, decomposer organisms, microbivores, and invertebrate herbivores and predators. The main pathways of energy and nutrient within the terrestrial study sites can be regarded as reasonably established. Net annual production locally reaches very high levels (up to 800 g m-2). Only a tiny part of this productivity is consumed by herbivores, the greater part passing to the decomposers or persisting as peat. Most of the animals are microbivores, or graze on fungi, and in turn sustain the small number of invertebrate predators. Analysis of the range of habitats even on Signy Island indicates however that the sites for which detailed ecological information is available represent only a part of the range of environmental and ecological variation. The island is in fact characterized by a very high level of within-site diversity, some of it on a very small scale. Similarly, recent research which permits ecological comparisons with the sub-Antarctic islands of South Georgia and Macquarie, and with the McMurdo area, confirms that Signy Island displays only a small part of the very large range of diversity within the Antarctic regions as a whole. It is a reasonably representative sample of the maritime Antarctic zone in the Antarctic Peninsula region where conditions are particularly favourable for terrestrial life. Its ecological features resemble most closely those of the South Shetland Islands (except over permeable volcanic rocks) and the Palmer Archipelago on the western side of the Antarctic Peninsula. Very different plant and animal communities occur over much of the McMurdo Sound region and in the inland ranges of East Antarctica. Some general statements can now be made about the relationships between terrestrial Antarctic eco-systems and climatic, edaphic and historical factors. There is a clearly marked attenuation of the vegetation and fauna and simplification of the ecological systems as one moves towards cold, arid continental conditions. But the biota of the maritime Antarctic and the sub-Antarctic islands is more impoverished than ecological factors alone would indicate, because of the isolation of these land habitats, many of which have only recently been deglaciated. If present environmental conditions persist, a slow increase in the complexity of these ecological systems is to be expected and in some areas, especially the subantarctic islands, this process is being accelerated by human influence.

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