If there is no selective survival based on shell thickness within a population of snails, what happens to shell thickness in response to crab predation?

Alaska and northern canada have a diet rich in vitamin d and their skin color is darker than predicted on the basis of iv intensity at their latitude. explain the observation:

Aboy with an extra x chromosome probably has which of the following syndromes?

Which of the following would be an important part of a multi-step plan to restore the stability of the red-cockaded woodpecker's ecosystem?