TOEFL Speaking Task 3

In behavioral ecology, the term “optimal foraging” refers to the idea that animals make feeding decisions that maximize the net energy gain per unit of time spent foraging. This means they weigh the energy obtained from a food item against the energy and time costs of finding, handling, and consuming it. Animals are expected to prefer prey or feeding strategies that offer the highest energy return for the least effort, while ignoring options that are less efficient, even if those options are abundant or easy to access.

Professor: Let me give you a concrete example from a study on bluegill fish in a freshwater lake. These fish feed on small water fleas, but not all fleas are equal. Larger fleas are more nutritious, but they are also faster and harder to catch. Smaller fleas are slower and easier to catch, but they offer much less energy. When researchers observed the bluegills, they found that the fish selectively ignored the tiny, easy-to-catch fleas, even when those were plentiful. Instead, they spent extra time and energy chasing the larger, faster fleas. Why? Because the energy gained from one large flea was far greater than the energy spent in chasing it, while catching many small fleas would not have repaid the energy cost. So the bluegills were maximizing their net energy gain, exactly as the concept of optimal foraging predicts.