What type of selection is pictured here?

What type of selection is pictured here?

A particular bird species lays an average of 4 eggs per nesting season. If more than four eggs are produced, the parents may not be able to feed the hatchlings. If less than 4 eggs are produced, there is an increased risk that predators will take all the young that have been produced.

A lizard population lives in a very rocky area consisting of black rocks and white rocks. Black lizards can hide from predators by living on black rocks, and white lizards can hide from predators by living on white rocks. The intermediate grey colored lizard is found in fewer numbers because of its inability to hide from predators in this environment.

During the ice ages, the black bears of Europe increased in size.

In a population of field mice, coat color ranges from light tan to dark brown. Medium brown mice are found in greater abundance due to their ability to blend in with their surroundings.

A population of Madagascar hissing cockroaches lives in a woodpile. It suffers predation from lizards. The lizards are unable to eat the very largest adult cockroaches, and instead prey upon small and medium sized adults. Eventually, the population of cockroaches has more large members overall.

In Darwin’s finches, beak size affects the mating call by changing the sound of the song. Birds with a medium sized beak attract fewer mates due to the unpopularity of their mating call.

A particular environment experienced high rainfall over several seasons. During these wet years, small seeds were much more common than large seeds. Finches with smaller beaks thrived, and produced more offspring than finches with larger beaks.

In a particular species of cactus, the number of spines on the stem determines their ability to survive and reproduce. A plant with too few spines is often eaten by thirsty herbivores. A plant with too many spines is often invaded by parasitic insects because the insects lay eggs at the base of the spines. Cacti plants with an average number of spines thrive in the environment.

This is the most common type of selection and results in a high degree of similarity between members of the population.