Read the section “gaining biodiversity.” describe geographical isolation and competition. (site 2) gaining and losing biodiversity globally, the natural mass has decreased over time, although the great mass extinctions have decreased it for a while. the most famous of the mass extinctions is the one claimed to be the dinosaurs, but we are currently in the midst of a human-created mass extinction. local diversity, on the other hand, is constantly increasing and decreasing at very short time scales. there are many factors that affect diversity, and the best natural circumstances are given here. human-generated, in, have always been negative, and are covered in the conservation issues section.