Ariver separates two groups of mice, one black and the other all white. a beaver dam allows the mice to cross the river. over time, many gray mice are born. the river is lined with light stones. gray mice are most visible to hawks that fly overhead and feed on mice. although many gray mice are born, not many live long enough to reproduce. what is this an example of?

Disruptive selection

Explanation:

Disruptive selection is a type of natural selection that occurs when the extreme phenotypes have increased survival fitness that the phenotypes with the intermediate trait. The disruptive selection favors the extreme phenotypes at the expanse of the intermediate phenotype.

In the given example, the intermediate phenotype (the gray mice) have lesser survival fitness as they are visible to predators. The disruptive selection does not favor gray mice and leads to the evolution of populations of black and white mice.  

the solute can move "downhill," from regions of higher to lower concentration, relying on the specificity of the protein carrier to pass through the membrane. this process is called passive transport or facilitated diffusion, and does not require energy.