A keystone species is a species that an ecosystem largely depends on, and if that species were removed, it would largely effect the ecosystem.

The keystone species of the biome that the Red Panda also lives in, is the Asian Elephant, that's commonly referred to as the 'keystone' species. The Asian Elephants, "Help to open up forest clearings and distributes the seeds of trees and shrubs."

If the Asian Elephants weren't around, the Red Pandas wouldn't be able to find as much food, and they would lack resources, because the Asian Elephants help distribute the seeds of trees and shrubs.