WATER AS A LIMITING FACTOR IN THE ANTARCTIC TERRESTRIAL ENVIRONMENT - A BIOGEOGRAPHICAL SYNTHESIS

The question is posed: ''what limits the presence, distribution, and abundance of life in Antarctica?'' Traditionally, continental isolation has been considered to restrict the arrival of new species and extreme cold to limit the survival of successful immigrants. However, recent biogeographical evidence suggests that water may play a primary role: clear correlations exist between moisture availability and the distribution and abundance of organisms on the vertical, horizontal, and temporal scales. At the continental scale there is a close relationship between substratum biotic/abiotic status and gradients in meltwater, seepage, and up-welling. At the microhabitat level, the abundance of nematodes, tardigrades, rotifers, and microarthropods is directly proportional to microvariations in relative humidity. Upward migration of soil microalgae in response to water availability, together with seasonal population peaks of bacteria, algae, and protozoa at snow-thaw, suggest moisture limitation on vertical and temporal scales. It is concluded that, in Antarctica, many of the limiting effects previously attributed to low temperature may in fact operate through the water balance of organisms. Although Antarctica is the coldest place on Earth, water appears to be the primary limiting factor.