The correct answer is C. They compete with native species for food and water.
It doesn't really matter are the newly introduced species into some territory predators, omnivores or herbivores. The problem is the competition. When new species are introduced, usually they are species that are better evolved then the native species. Take Australia for example. Predators, omnivores, herbivores, all have similar effects when free in the wild and compete with the native species. The predators kill the native species with ease cause they do not have defense mechanism for them. The herbivores are reproducing much faster then the native ones, push them away, and reduce their food supply. The omnivores take niche that is free and also out compete the local herbivores with ease.
