With a single species, competition is more intense because the one specie because if the one prey they hunt is scarce, then the whole specie has a chance of dying out quicker. With two different species, they have a wider variety of prey they can hunt, who knows, the two species may hold a separate niche which can help them surpass the competition. With a singular specie with the same niche having competition, then they're niche has a greater chance of dying out. Even if one animal's niche collapses entirely, this could lead to a whole ecosystem collapsing--Considering the fact that each animal's niche is equally important to the ecosystem.
