Top predators disappearing from ecosystems can lead to changes in prey animals. In a study with guppies, moving them from a predator-rich to a predator-free environment caused them to evolve better at finding food. This shift in natural selection made the guppies more efficient eaters, impacting the lower levels of the food chain. The absence of top predators can lead to prey species becoming better at feeding, which can have big effects on the whole ecosystem.