Ecology - Rarity as double jeopardy

What factors contribute to extinction of a species? Conventional wisdom has it that those species that have many members (high abundance) spread over a large geographical range have a greater chance of survival than less abundant, clustered populations. But it turns out that this is not all. A study of Australian marsupials now reveals that species of a relatively recent evolutionary origin show a positive relationship between local abundance and geographical spread, whereas more ancient species show a negative relationship. Presumably, this is because the relatives of ancient species who showed low abundance and small ranges have already become extinct.