you say react as if there's an awareness by the group of organisms that they are dying out, when that's far from the truth. Think of a species as a network, with the leaf nodes around for only a specific length of time. Add in several events that isolate portions of the network, and it dies off in spurts, as each isolated portion becomes less fit and eventually ceases reproduction.

With the decline in our birthrate, it will be interesting to see (from a historical perspective, I'll be long dead) if we die out, or if we get out of this funk we're in now.