听力材料：
Speaker 1:Listen to part of a lecture in a biology class.
Speaker 2:So. We've been talking about the different ways animals can benefit from being in a large group. And, well, one important benefit is the added protection they get, protection from predators. One major concern during an animal's lifetime is survival. And, being part of a large group allows animals to provide protection for one another. Let's discuss two ways that being a part of a large group can contribute to animal survival.
For one thing, if a large number of animals are together in a group, this overwhelms predators. That is, predators don't have time to catch them all. If they were alone, predators could pursue each of them, but because they are together, the predators can only go after a few. As a result, the survival rate of the majority increases. For example, when bats are resting in a cave. When they leave the cave, bats often fly out all at once. And, well, then predators waiting outside the cave only have time to catch a few bats.
A second benefit is um, animals in large groups can warn other animals that a predator is nearby. That's because if one member of the group sees a predator, it can act in a way that lets other members know there's danger, and even the animals who never saw the predator, have time to get away quickly.
One of the most interesting examples of this is an insect called the Ocean Skater. They travel in large groups across the surface of the ocean. And, since the ones on the edge of the group are most likely to see predators coming, they warn the rest of the group of approaching danger.
Question：
Using the examples of bats and ocean skaters, explain how animals benefit from being in a large group.
