In order for natural selection to change a trait within a population, what must be true about the trait?

Explain the side effects of cancer treatments

Several bird species feed in a certain species of tree. each bird species feeds in a different part of the tree. which statement is true of these bird species? a. they have adapted to different niches due to competition b. they have a carnivorous relationship with the tree species. c. they have adapted to different niches due to predation d. they have a symbiotic relationship with the tree species.

Babies with very low or very high birth weight are less likely to survive. observe a graph of the data.