As we don't know what the vast majority of species are, studying their extinction on a case by case basis isn't going to get very far. What we do know with a pretty high degree of certainty is that man has displaced species of every type in every environment which supports human life (and a great many don't but which serve as receptacles for our waste.) And what we also know is that the trends in extinction show that the current rate is vastly higher than the background rate.