Populations


While many people think of species as single, constant, easily identifiable entities, species are usually composed of multiple, continuously changing populations. These populations may differ in subtle or striking ways - due in part to the unique genetic composition of the individuals in them. Some species of Heliconius butterflies, for example, show dramatic differences in mimicry coloration across populations.

Many plants commonly exhibit differences in their life cycles in different populations, even when grown under the same experimental conditions. For example, plants taken from alpine populations tend to grow slower, bloom at smaller sizes, and have longer seasonal dormancy periods than individuals taken from lower elevations.

Since individuals are more adapted to their local environmental conditions than to those elsewhere in the species' geographic distribution, they usually cannot easily replace members from another population in a different place. In wild species, this range of genetic attributes within and among populations facilitates the long-term adjustment of populations to changing environmental conditions.

In agriculture, this genetic variation is the source of continued breeding of new varieties. Throughout human history, people have mimicked these natural adaptive processes in their domestication and breeding of varieties of animal and plant species - to suit various cultivation techniques or microclimates.

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