Extreme environments

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

Terrestrial polar

Marine polar

Saline lakes Mountains

Deserts

Temporary deserts Temperate mid-winter

Deep sea Hot springs Hydrothermal vents

Cold

Desiccation Cold

Salt

Temperatures, desiccation, ultraviolet radiation, oxygen

Heat

Desiccation Desiccation

Cold Food availability Pressure Heat

Periodic Seasonal

Unpredictable

Constant Periodic

Daily & seasonal

Unpredictable

Periodic Daily & seasonal

Unpredictable

Periodic Unpredictable Unpredictable

Periodic Seasonal

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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