Subject: Are lions and leapords 2 keystone predators in the same ecosystem?

Today in class my environmental science teacher was discussing a theory that 
states there can only be one keystone predator in an ecosystem. He said that 
two species cannot have any of the same resource requirement (like food) or one 
will die. I thought about lions and leapords who have the same food sources and 
share territory. He said that there is probably a subtle partition in the diets 
of these animals. I know that they hunt differently and have different 
behaviors, but they eat basically the same prey. Consequently they are in 
competition, but both species are surviving. Could this be an exception to the 
theory? Or is there a difference that I've overlooked that allows them to co-
exist under this theory? 

Thank you for your help and time! I'm very curious to recieve an answer.
Sincerly,
Mollie
(future middle school science teacher)

Re: Are lions and leapords 2 keystone predators in the same ecosystem?