Effects of Past Global Change on Life (1995)
Chapter: CLIMATE TOLERANCES OF TROPICAL ORGANISMS
FIGURE 6.3 Simulated surface salinity (%0) with contour interval of 1%0: (a) mid-Cretaceous, minimum 34.5%0; (b) Paleocene, minimum 32.5%0; (c) Eocene, minimum 33.5%0; (d) Miocene, minimum ,<32.5%0; (e) present day, minimum <32.5%0.
ticularly interesting for global change studies and for considering the tropical response to increased levels of carbon dioxide in the near future. The key question becomes the significance of increases of 3 to 5°C in surface temperature and of several parts per thousand in salinity on the distribution and character of tropical organisms.
CLIMATE TOLERANCES OF TROPICAL ORGANISMS
Abundant evidence exists demonstrating that climate is a significant limiting factor in the distributions of organisms (e.g., Valentine, 1973; Stanley, 1984a,b). The tropics are generally viewed as an environment in which the physicochemical constraints are not undergoing major changes, resulting in an environment that is limited largely by biological competition. However, many equatorial species are also characterized by narrow environmental tolerances, suggesting that relatively small temperature and salinity changes could result in a substantial biologic response. Stanley (1988) suggests that tropical cooling could result in extinction if the temperature decrease removed the warm climate conditions required by many tropical organisms. In the case of hermatypic coral diver-
