How does an animal choose what food to eat? One might assume that natural selection has influenced the foraging behaviors of animals, and that most animals forage efficiently, spending the least energy to gain the most nutrients.

The accompanying animation is based on the results of an experiment on the feeding behavior of bluegill sunfish. Ecologists performed laboratory experiments with these fish to determine their foraging strategies when presented with different sizes of the water flea Daphnia. Before performing the experiment, the investigators predicted that in an environment stocked with low densities of all three sizes of prey, the bluegills would take every water flea that they encountered, but that in an environment with abundant large water fleas, the fish would ignore the smaller ones.


From the foraging experiment described in the animation, bluegill sunfish appear to be energy maximizers. That is, when prey are in low supply, bluegill maximize their rate of energy consumption by eating prey of any size encountered. When prey are plentiful, however, bluegill become selective and eat only the most energy-rich prey. At these high densities of water fleas, bluegill maximize their rate of energy intake by preferentially eating the larger prey.

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Textbook Reference: Concept 40.6 Behavior Helps Structure Ecological Communities and Processes