Big, fierce animals — lions and tigers and bears, for example — are relatively scarce in nature. That's normal, because if you have too many, they'll eat themselves out of prey.
But top predators are now so rare that many are in danger of disappearing. That's creating ripple effects throughout the natural world that scientists are still trying to figure out.
What they're exploring is ecology — the interplay of animals and plants in nature. It's not rocket science. It's harder.