When mosquitoes are abundant, purple martins flock to the area and feed exclusively on them. When mosquito populations are not large, purple martins are similarly scarce and feed on other insects. This is an example of

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Quizplus · Accepted Answer

This is an example of density-dependent regulation because the population size of purple martins is directly related to the population size of their food source, mosquitoes. When mosquitoes are abundant, purple martins increase in number as their food source is plentiful, and when mosquitoes are scarce, the purple martin population decreases. This shows a direct dependence of one population on the density of another population for its regulation.

When Mosquitoes Are Abundant, Purple Martins Flock to the Area