concept

Extinction debt

Extinctions that have already been caused but not yet paid. Tilman and colleagues named it in 1994: when habitat is destroyed, the dependent species do not all die at once — the mobile and long-lived ones are still there the next morning, foraging in the surrounding forest even though the thing they bred in has gone. But their reproduction has already fallen below their deaths, and the rest is arithmetic. They persist for a season, a decade, sometimes a century, as a population going quietly to zero. Which is why a damage assessment taken on the day always understates the true toll.