托福口语 Task 4

Today we're going to discuss a concept in behavioral ecology known as 'optimal foraging theory.' Simply put, this theory suggests that animals have evolved to maximize the net energy gain from their foraging efforts while minimizing risks and costs. In other words, they don't just eat anything; they make choices that give them the most benefit for the least energy and danger. Let me give you two examples. First, consider the Northwestern crow. These birds feed on whelks—a type of marine snail. To eat them, crows drop the whelks from a height to crack the shells. But they don't drop them from very high up. Instead, they choose a drop height that balances the energy spent flying up and the chance of breaking the shell. Dropping from too low wastes time and energy on repeated attempts, while dropping from too high wastes extra energy for no additional benefit. They've learned to choose an optimal height. Second, think about the bluegill sunfish. When hunting for water fleas, these fish selectively feed on the largest, most energy-rich prey, even though smaller fleas are more abundant. The larger fleas provide more calories per unit of effort, making them the better choice for the fish's energy budget. So, in both cases, the animals are making decisions that maximize energy return while minimizing unnecessary costs.