Different extreme environments present different challenges to the organisms that inhabit them. Table 8.1 outlines the main extreme environments that were described in Chapter 2. These environments differ in the major physical and biological stresses they present to organisms, whether the stress is constant or varies and, if it varies, whether it is predictable. A periodic stress may have a degree of
Table 8.1 Classification of extreme environments
Extreme Major environment stresses
Predictability of periodic stress Constancy _
of stress Long term Short term
Saline lakes Mountains
Temporary deserts Temperate mid-winter
Deep sea Hot springs Hydrothermal vents
Temperatures, desiccation, ultraviolet radiation, oxygen
Cold Food availability Pressure Heat
Daily & seasonal
Periodic Daily & seasonal
Periodic Unpredictable Unpredictable
Unpredictable predictability on a long-term basis since conditions are likely to be harsher during one season than another and harsher during the day than they are at night. Conditions may be unpredictable on a short-term basis, with temperatures and water availability changing on a daily, or even an hourly, basis. Where the stress is constant (as in polar seas, saline lakes, hot springs), the organisms must use capacity adap-
tation with their biological processes functioning under the conditions that are experienced in their environment. Where the degree of stress changes on a seasonal basis, organisms can respond by a period of dormancy (such as hibernation) and/or the production of compounds that aid survival of the stress (such as the seasonal production of antifreezes by some polar and temperate invertebrates). Periodic stress is likely to favour resistance adaptation, with the organism surviving the extreme conditions in a dormant state until conditions favourable for growth and reproduction return.
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