What is the explanation for the pattern of population density of a species?

Question

There have been two species of leaf-eating beetles on an island in the Pacific Ocean for 100,000 years and a new species of a leaf-eating beetle was placed on the island accidentally. The population of the new species has consistently increased and now there are more of the new beetles than there are of the two other species that have been there for a 100,000 years. What is the explanation of this?

Answer 1

Competitive Exclusion - the new species is a better competitor than the original two and upon its arrival it takes over the habitat, excluding the previous species.