LESSONS FROM A KILL

During their colonization by Polynesians and later by Europeans, the H awaiian islands suffered a massive loss of species. All the extinction s are indirectly attributable to human impact. Nonetheless, it has pro ved extremely difficult to specify which of several possible mechanism s caused each particular extinction. This seems to admit defeat in the battle to understand past extinctions. Such understanding could guide our efforts to protect species that are now threatened with extinctio n. Will it be easier to understand the causes of future extinctions? S urveys of future extinctions stress habitat destruction as the simple and dominant mechanism. This contrasts to its secondary (and generally confused) role in past extinctions. I argue that this contrast betwee n the complexity of the past and the apparent simplicity of the future arises because extinction mechanisms are inherently synergistic. Once extensive species losses begin, it may be impossible to separate the mechanisms and thus manage an individual species as if its decline had a single cause.