This occurs when a large population is drastically reduced by an event such as a natural disaster; the population's new gene pool only contains alleles from the survivors

If thick-shelled oysters are tougher to crack open than thinner shelled oysters, crabs will be less able to prey upon them, and thick-shelled oysters will be more likely to survive and reproduce. What kind of selection occurred?

Average phenotypes are favored in the environment, while extremes have lower survival rates.

Light colored cray fish are hard for a predator to see because they blend into the rocks. Dark colored cray fish blend into the shadows cast by the rocks. Intermediate colors are most heavily preyed on.

Female robins can lay anywhere from 1-10 eggs. Laying too few eggs runs the risk of them all getting eaten, and laying too many eggs results in malnourished (they don't get enough to eat) chicks. Most robins will lay 4-5 eggs.

Frogs with longer tongues are able to catch more food. Frogs with short tongues can't catch as much food and don't usually survive.

Which graph shows disruptive selection?

In sunflowers, being too short means not getting enough sunlight. Growing too tall means getting blown around by the wind. Medium height sunflowers tend to survive the best.