An example of density-dependent regulation in mammals: hare populations fluctuating due to resource limits and predator pressure.

An example of density-dependent regulation in mammals: hare populations fluctuating due to resource limits and predator pressure.

• A. Hare populations fluctuate due to resource limits and predator pressure.
• B. Population size remains constant regardless of resources.
• C. Density-dependent regulation increases growth rate as density increases.
• D. Predators have no effect on prey populations.

Answer: (A)

Density-dependent regulation means a population’s growth and size are shaped by how crowded it is, with factors like food limits, competition, and predator pressure changing as density changes. In mammals such as snowshoe hares, higher hare density can deplete resources and lead to more encounters with predators, pushing birth rates down and death rates up. When numbers decline, resources rebound and predator impact per individual lessens, allowing the population to recover, which creates the characteristic fluctuations. This hare example directly shows how regulation depends on density, not a fixed, resource-independent size. The other ideas don’t fit because staying constant regardless of resources describes density-independent dynamics, not density-dependent regulation. Saying growth rate increases as density increases contradicts the typical pattern that crowding reduces per-capita growth due to competition. And claiming predators have no effect ignores the predator–prey interactions that drive these density-dependent cycles.

Density-dependent regulation means a population’s growth and size are shaped by how crowded it is, with factors like food limits, competition, and predator pressure changing as density changes. In mammals such as snowshoe hares, higher hare density can deplete resources and lead to more encounters with predators, pushing birth rates down and death rates up. When numbers decline, resources rebound and predator impact per individual lessens, allowing the population to recover, which creates the characteristic fluctuations. This hare example directly shows how regulation depends on density, not a fixed, resource-independent size.

The other ideas don’t fit because staying constant regardless of resources describes density-independent dynamics, not density-dependent regulation. Saying growth rate increases as density increases contradicts the typical pattern that crowding reduces per-capita growth due to competition. And claiming predators have no effect ignores the predator–prey interactions that drive these density-dependent cycles.