An animal’s habitat (environment) includes all living (biotic)
and nonliving (abiotic) characteristics of the area in which the
animal lives. Abiotic characteristics of a habitat include the availability
of oxygen and inorganic ions, light, temperature, and current
or wind velocity. Physiological ecologists who study abiotic
influences have found that animals live within a certain range of
values, called the tolerance range, for any environmental factor.
At either limit of the tolerance range, one or more essential functions
cease. A certain range of values within the tolerance range,
called the range of optimum, defines the conditions under which
an animal is most successful.
Combinations of abiotic factors are necessary for an animal to survive and reproduce. When one of these is out of an animal’s tolerance range, it becomes a limiting factor. For example, even though a stream insect may have the proper substrate for shelter, adequate current to bring in food and aid in dispersal, and the proper ions to ensure growth and development, inadequate supplies of oxygen make life impossible. Often, an animal’s response to an abiotic factor is to orient itself with respect to it; such orientation is called taxis. For example, a response to light is called phototaxis. If an animal favors well-lighted environments and moves toward a light source, it is displaying positive phototaxis. If it prefers low light intensities and moves away from a light source, it displays negative phototaxis.
Combinations of abiotic factors are necessary for an animal to survive and reproduce. When one of these is out of an animal’s tolerance range, it becomes a limiting factor. For example, even though a stream insect may have the proper substrate for shelter, adequate current to bring in food and aid in dispersal, and the proper ions to ensure growth and development, inadequate supplies of oxygen make life impossible. Often, an animal’s response to an abiotic factor is to orient itself with respect to it; such orientation is called taxis. For example, a response to light is called phototaxis. If an animal favors well-lighted environments and moves toward a light source, it is displaying positive phototaxis. If it prefers low light intensities and moves away from a light source, it displays negative phototaxis.
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