| Summary: | Anyone who is even slightly acquainted with plants or animals knows that different species inhabit different parts of the world, live in different habitats, and, in the case of animals, eat some imaginable kinds of food and not others. As with many other familiar facts, it may not occur to us to ask why the geographic and ecological ranges of species are limited, until we realize that species vary drastically in their geographic, ecological, and physiological amplitudes. The bracken fern (Pteridium aquilinum) is broadly distributed in temperate climates of every continent (except Antarctica), whereas the curly-grass fern (Schizaea pusilla) is limited to parts of eastern Canada and central New Jersey in the United States. The black-billed magpie (Pica pica) is a familiar bird from western Europe through eastern Asia and from Alaska to the Great Plains of North America, but the very similar yellow-billed magpie (Pica nuttalli) is restricted to central California. What accounts for the much narrower distribution of one than the other species? Related species often differ in the variety of habitats they occupy. The thistle Cirsium canescens is restricted to well-drained sandhills in the American prairie, whereas Cirsium arvense is a European species that has become a rampant weed in North America, growing in many types of soil. The endangered Kirtland's warbler (Dendroica kirtlandii) nests only in stands of jack pine of a certain age, while its relatives, such as the yellow warbler (Dendroica aestiva), nest in many types of vegetation and have far broader geographic ranges as well. (Species with narrow and broad habitat associations are referred to as stenotopic and eurytopic, respectively.) Stenotopic species or populations frequently have a narrower tolerance of certain physical variables than do others. Most plants and animals from warm tropical environments cannot survive freezing temperatures, and Antarctic notothenioid fishes cannot tolerate temperatures above 6°C. In contrast, species that inhabit ...
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