Altitudinal Limits of Life in Subtropical Mountains: What Do We Know?

Abstract

Present knowledge of the highest altitudinal limits of organisms and their causes is reviewed. Discussion focuses on subtropical latitudes (20- 30°) and altitudes above 4000 m. Methods used in high-altitude studies are limited by logistical and biological factors. Use of a comparative convergence-divergence method is encouraged. Terms such as "extreme" are inappropriate in the description of environments with moderate temperature amplitude, positive water balance, and rich soils but low atmospheric pressure. Characters such as slow productivity, frugal behavior, stress tolerance, crypts, large number of stomata, greater development of lungs and circulatory systems, hygromorphy, heliomorphy, protection, insularity, high diversity , and a decreasing plant/animal ratio are considered typical of organisms in these altitudes (hypsophily). Hypotheses explaining some of the characters are discussed.