“Diversify your portfolio” is great advice—and not just for investments. The math that backs it up turns out to explain much more than stock market returns.
Biologists came up with the idea of a “portfolio effect” more than 15 years ago, as a useful model—borrowed from finance—to explain the relationship between diversity and stability in living systems. The more species there are in an ecosystem, the more stable it should be. A finance analogy is also helpful because animal populations sometimes crash like stock prices do. Now, a new paper in the Proceedings of the National Academy of Sciences (PNAS) may make it easier to investigate why these ecosystem crashes happen, by amassing into one place 75 years of data about fish, marine mammals, birds, reptiles, and others.