An entire continent is covered with Eucalyptus trees. They suck the moisture out of the entire surrounding area and use allelopathy to ensure that most of what’s beneath them is just bare red dust. No animal is making use of them——they have virtually no herbivore predator. A niche is empty. Then inevitably, natural selection fills that niche by creating an animal which can eat Eucalyptus leaves. Of course, it takes great sacrifice for it to be able to do so——it certainly can’t expend much energy on costly things. Isn’t it a good thing that a niche is being filled?

Sounds like I have my answer for next week’s question of “what’s the worst plant on Earth”