Are Numbers of Species a True Measure of Ecosystem Health?

A coral reef near the Indonesian island of Bali. Shutterstock


Are Numbers of Species a True Measure of Ecosystem Health?

A recent study that found no general decline in the numbers of species in individual ecosystems has sparked controversy. Some scientists see it as evidence of how species adapt, while others see it as a sign that common invasive species, such as rats and mosquitoes, are the real winners.

By Fred Pearce • November 12, 2019


A great extinction is under way across most of the planet. From the forests of the Amazon to the suburban hinterlands of America, from the depths of the oceans to Southeast Asia’s mangrove swamps, millions of species are being lost. And as species disappear, the populations of those that remain are also plunging. North America has lost more than a quarter of its birds since 1970.

And yet the situation is more complex than at first sight. Many local ecosystems — at least as measured by “species richness,” the number of species they contain — appear to be in good health. The most comprehensive count ever attempted of species numbers in local ecosystems last month came up with two unexpected and controversial results…