When mosquitoes are very abundant, purple martins flock to the area and specialize on them. when mosquito populations are not large, purple martins are similarly scarce and feed on other insects. this is an example of
a) community carrying capacity.
b) ecosystem carrying capacity.
c) exotic regulation.
d) density-independent regulation.
e) density-dependent regulation

The correct answer is E) density-dependent regulation.

Explanation:

When the population growth rate is dependent on the density of a population then it comes under density-dependent regulation. Usually, when a population becomes denser the mortality rate becomes high in that population.  

This regulation can occur due to factors like predation, disease, inter or intraspecies competition. So here when the density of the mosquitoes becomes high then purple martin flock to the area and specialize in them to gain nutrition which stabilizes the population of mosquitoes again.

Density-dependent regulation is more significant when the population density of a species increase. So the right answer is E.

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