Is species richness increasing or decreasing?

Posted by Richard B. Primack, Abraham J. Miller-Rushing, and Vincent Devictor

“It takes two to speak the truth, - one to speak, and another to hear.” 

-Thoreau in A Week on the Concord and Merrimack Rivers

Conservation biologists have argued that we need to protect local species richness (i.e. the number of species found locally) for its value in providing ecosystem services, such as clean water, flood control, and pollination. Yet in a recent editorial in Biological Conservation, we report that many long-term ecological studies have found the surprising result that the number of species at sites around the world has remained stable or is even increasing. We have similarly found that the number of wildflowers in Concord, MA has increased from Thoreau’s time to the present.

A diversity of wildflowers grow in this Romanian meadow

How could this be true when hundreds of species have gone extinct, and thousands more are declining and threatened with extinction? The answer seems to be that the loss of species at the local scale is often balanced by the arrival and establishment of new native or nonnative species.

These findings highlight the need for conservation biologists to avoid oversimplification when selecting management indicators, such as species richness. Targeting only species richness ignores the ethical, cultural, and aesthetic values of certain local species and ecological communities, such as monarch butterflies and redwood forests. These aspects of biodiversity can still be damaged or lost, even as species richness remains steady or increases.

Richard Primack is a professor in the BU Biology Department.
Abraham J. Miller Rushing works for the National Park Service at Acadia National Park (and received his PhD at BU).
Vincent Devictor is a professor at the University of Montpellier in France.
A version of this article was originally published in the journal Biological Conservation.