USA Biology Olympiad (USABO) Practice Exam

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Populations living near the limit of their resources are characterized as what type of selection?

R-selected
K-selected
Stabilizing
Directional

The correct answer is: K-selected

Populations living near the limit of their resources are characterized by K-selected selection. This type of selection is associated with species that thrive in stable environments where competition for limited resources is high. K-selected species tend to have lower reproductive rates, longer lifespans, and invest more energy in raising fewer offspring. The 'K' in K-selected refers to the carrying capacity of the environment, which is the maximum population size that can be supported sustainably. In K-selected populations, individuals typically exhibit traits that enhance their survival and competitive abilities in an environment where resources are scarce. This contrasts with R-selected species, which produce many offspring with less investment in each, thriving in unpredictable or fluctuating environments with abundant resources. The other types of selection, stabilizing and directional, relate more to particular characteristics of a population rather than the condition of resource limitations. Stabilizing selection favors average traits, while directional selection favors one extreme trait over time, neither of which specifically addresses the impacts of resource limitations as K-selection does.