Animal populations have fallen since the 70's

Wild animal populations (of birds, fish, amphibians and reptiles) have fallen 70% on the average since 1970.

When a population becomes small and localized, it is at high risk of being wiped out by random events. One wildfire, one storm, one new mine, one new housing development, and it could be gone. Mines and housing are made by humans; nowadays, wildfires and storms are, too.