How important are big animals to their ecosystems?
Short answer: Very.
Longer answer: Scientists are finding more and more examples of ecosystems devastated or destabilized by human-caused removal of large animals. From savannah ruined by fire after grazing wildebeasts were wiped out, to deforestation as new saplings and seedlings were eaten by rodents in regions without big cats, the negative effects of man on nature are well documented.
Above is Long Lake in Michigan, where researchers artificially split the lake and removed largemouth bass (left). The cleared portion of the lake became oxygen- and nutrient-depleted, and was overrun by algae and small invertebrates. It’s a dramatic demonstration of how single species can keep an entire ecosystem in equilibrium, and knocking them out can have ruinous effects.