Loss of diversity makes everything verse

OK, the pun was terrible. But the point is important. Why does life survive mass extinctions, and why does it take longer in some cases to recover species diversity than in other cases? Scientists looking at the Permian-Triassic extinction, 250 MYA, say they can trace cause and effect. Loss of diversity begets more loss of diversity, and recovery is slower when there are fewer species (in other words, fewer respoitories of unique genomes) to work with. It may be worse when it's the big (apex) predators and herbivores are the ones to go. As Prof Jessica Whitesides, concerned about modern extinctions, puts it, “We’re showing that low-diversity systems take a long time to recover. When you destroy links in the food web, effects exist that are difficult to see. Normally when people think of extinctions, it’s of single species. This is a systems approach.”