concept

Co-extinction

The loss of a species because the species it depended on is gone. Koh and colleagues (2004) showed the shape depends entirely on how fussy the dependent is: a generalist that can use many hosts hangs on as its hosts vanish one by one, collapsing only when the whole host network passes a threshold. But a strict obligate, tied to one host and no other, follows a straight one-to-one line — its host goes, it goes, with no adjustment period and no alternative. This is why ash-dieback researchers can name a doomed number of species now, before the deaths have happened.