In addition to physical stresses, organisms also face a number of biological stresses. These include competition with other organisms, predation, diseases and parasites, and the availability of food. Organisms that are able to survive or thrive under conditions which other organisms cannot are thus at an advantage. They can avoid competition by utilising habitats and food sources that are not available to others. Predators, parasites and diseases, which might otherwise affect them, may also be absent in their extreme homelands. In order to survive their unusual living conditions, extreme organisms have had to solve the problems and challenges posed by the stresses they experience. Extreme organisms take us to the outer edge of biology, an extreme biology, giving us new insights into the nature of life.
In the next chapter of this book, I will look at the different types of extreme environments found on Earth. The next three chapters deal with how some organisms cope with the main types of physical stress they experience in extreme environments: desiccation (Chapter 3), heat (Chapter 4), cold (Chapter 5), and pressure, pH extremes, osmotic stress, lack of oxygen, radiation and toxins (Chapter 6). In chapter 7, I will consider how studies on extreme organisms may help us in our search for extraterrestrial life and I will look at some general features of extreme biology in Chapter 8.
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