Body size is a heritable trait in the amphipod, an aquatic crustacean. Fish preferentially consume large amphipods, leaving primarily small amphipods to breed. Based on these observations, how would we expect evolution to affect ponds with and without fish?

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In ponds with fish, the selective pressure is for smaller body size, as larger amphipods are preferentially eaten. Therefore, over time, we would expect to see smaller amphipods in ponds with fish compared to ponds without fish.

Body Size Is a Heritable Trait in the Amphipod, an Aquatic