Defining the Niche Describing a species' “address” tells only part of its story. Ecologists also study a species' ecological “occupation”—where and how it “makes a living.” This idea of occupation is encompassed in the idea of an organism's niche (nich). A niche describes not only what an organism does, but also how it interacts with biotic and abiotic factors in the environment. A niche is the range of physical and biological conditions in which a species lives and the way the species obtains what it needs to survive and reproduce. Understanding niches is important to understanding how organisms interact to form a community.

▸ Resources and the Niche The term resource can refer to any necessity of life, such as water, nutrients, light, food, or space. For plants, resources can include sunlight, water, and soil nutrients—all of which are essential to survival. For animals, resources can include nesting space, shelter, types of food, and places to feed.

▸ Physical Aspects of the Niche Part of an organism's niche involves the abiotic factors it requires for survival. Most amphibians, for example, lose and absorb water through their skin, so they must live in moist places. If an area is too hot and dry, or too cold for too long, most amphibians cannot survive.

▸ Biological Aspects of the Niche Biological aspects of an organism's niche involve the biotic factors it requires for survival. When and how it reproduces, the food it eats, and the way in which it obtains that food are all examples of biological aspects of an organism's niche. Birds on Christmas Island, a small island in the Indian Ocean, for example, all live in the same habitat but they prey on fish of different sizes and feed in different places. Thus, each species occupies a distinct niche.

FIGURE 4–5 Competition Animals such as these two male stag beetles compete for limited resources. Infer What resource do you think these two males are fighting over?

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