托福口语 Task 3

In behavioral ecology, the term 'optimal foraging' refers to the idea that animals will choose feeding strategies that maximize their net energy gain while minimizing the costs of obtaining food. This does not mean they always eat the most nutritious food, but rather they balance energy spent searching, capturing, and handling prey against the energy received. Foragers are predicted to select food items that offer the highest energy return per unit of handling time, and to abandon a patch when the rate of energy gain drops below the average for the habitat.

Professor: So, let me give you a classic example—the bluegill sunfish. When these fish feed on small water fleas, they don't just eat any flea they see. They actually choose larger, more energy-rich fleas, even if smaller ones are more abundant. Why? Because capturing a large flea takes almost the same time and effort as capturing a small one, but the large flea provides much more energy. So, the fish maximize their energy per capture. Now, here's the tricky part—when large fleas become scarce, bluegills don't just keep hunting them. They switch to smaller fleas. That's because the time spent searching for a rare large flea would outweigh the energy gained. By switching, they keep their net energy intake high. This behavior perfectly illustrates optimal foraging—they are not picky, they are efficient.