96% of marine animal species became extinct in the permian mass extinction at the end of the paleozoic, 252 million years ago. why does the blue curve show only a 50% drop at that time?

Ascientist is designing an investigation to study the impact of invasive bird populations on local, native bird populations at backyard bird feeders. what population is most likely to be a control group for the investigation? amount of food number of bird feeders invasive bird populations local backyard birdfeeders without food