The lecture is focusing on two disadvantages of living in a group for animals. One disadvantage is that animals living in groups are more visible and vulnerable to predators. Take sardines as an example. They swim in groups and they are prey for some large animals such as whales. Although it may be hard for a whale to notice one little Sardine, it is able to see a group of them and capture them for food. Another disadvantage is that living in groups set great barriers for animals to identify their own young and thus have them in good care. For example, one type of bats live together in the same cave with millions of them. With too much bats in the same cave, a mother bat may find it’s hard to find her own baby and she may end up feeding the babies of another mother bat, leaving her own babies with no food.