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Introduction to Populations

Author(s): Deanne Erdmann, MS

Reproductive Strategies

In an uncrowded environment, such as a recently abandoned crop field, natural selection pressure tends to favor populations that invest heavily in offspring, have shorter life spans, capacity for widespread dispersion, and usually provide little or no parental care for offspring (for example, mosquitoes, ragweed, or mice). These populations tend to increase exponentially and often are referred to as r-strategist, where r refers to the intrinsic rate of growth of the population. In contrast, crowed conditions favor organisms with lower rates of population growth, but improved capabilities to utilize and compete for resources. These populations maintain themselves at levels close to carrying capacity (K) and are referred to as K-strategist.

Biologist refer to the types of selection pressure placed on populations as r-selection, if individuals that reproduce rapidly and abundantly are favored, and as K-selection, if individuals that compete well in crowded conditions are favored over time.