Quote from : Ishmael: An Adventure of the Mind and Spirit Book

Diversity is a survival factor for the community itself. A community of a hundred million species can survive anything short of total global catastrophe. Within that hundred million will be thousands that could survive a global temperature drop of twenty degrees—which would be a lot more devastating than it sounds. Within that hundred million will be thousands that could survive a global temperature rise of twenty degrees. But a community of a hundred species or a thousand species has almost no survival value at all.