Well, depending on how long the migration is, many of the animals (mainly birds) could get sick and die, lowering the population. They could be shot by hunters, lowering the population. The children of the population could get left behind and lose their way, lowering the population. I'm not entirely sure how the population could grow other than them finding and staying with another group of their own kind. hope I was helpful! :)
Answer:
Anterior end
Explanation:
You have a pretty good shot at guessing this, because the earthworm has very little going on at the posterior end except the anus. And you probably saw this in lab, too.
I've attached a picture of the earthworm anatomy. Worms can't smell in the strictest sense, but they can use their receptors as kind of a combo smell-taste thing, and those are located in the anterior end.