By ELEANOR HEDGES DUROY, age 10

PHOTO: Wikimedia Commons
PHOTO: Wikimedia Commons

According to a study published in the Journal of Animal Ecology, the population of elk in northern Yellowstone National Park has decreased since gray wolves were reintroduced. This caused grizzly bear populations to increase because elk and bears eat the same berries. The study shows that lives in ecosystems are connected and how one change affects the entire system.