Question

A population of field mice is preyed on by a group of hawks. The mice that are smaller in size are able to quickly escape into burrows in the ground and avoid predation.
The mice of medium and large size are too large to fit into the burrows and are unable to escape the hawks. Over time, the mouse population is composed of mostly small mice.
What process is responsible for causing this outcome?

• A. Hardy-Weinberg equilibrium
• B. Diversifying selection
• C. Stabilizing selection
• D. Directional selection
• E. Sexual selection

Answer 1

The correct option is D Directional selection

The mice which are smaller in size are able to avoid predation because they are able to quickly escape into burrows in the ground while the mice that are large in size are not able to escape the hawks because they can't fit into the burrows. This shows natural selection where the small mice are able to survive because of their small size that makes them able to adapt in the conditions of predation by hawks.

Natural selection is of three types:

1. Directional selection: It occurs whenever the environment changes in a particular way and therefore, is a selective pressure for species to change in response to the environmental change.

2. Stabilizing selection: It occurs when the environment does not change. Natural selection has to produce change and if an environment does not change there is no pressure for well adapted species to change. Fossil evidences suggest that many species remain unchanged for long periods of geological time.

3. Disruptive selection occurs where an environmental change may produce selection pressure that favours two extreme characteristics.

Hence, the occurrence of small sized mice over time shows directional selection where the species of mice changed from large sized to small sized over a period of time in response to environment conditions of predation.

So, the correct answer is Directional selection.