hundreds - white-footed rock rats, certain types of hare wallabies, a lot of the smaller mammals that have been really nailed by the feral predators like cats, and foxes - in some cases it is probably not worthwhile putting a lot of effort because there's just no chance."He says the index is based on the probability of a species becoming extinct.
"If we have something that has a very poor safe index, we would just simply say that it has a higher probability of going extinct rather than something with a higher safe index," he said.
"It is a probability, so it is not saying it will go extinct. It is saying it just has a much higher probability of going extinct."
He says the index is likely to generate debate.
"Decisions have to be made within the context of science and social consideration.
"I think that certainly people will argue with me that we should save everything.
"I'd love to save everything. I just don't think we can."
- ABC News