On the meanings of nestedness: back to the basics

The ecological concepts of nestedness and beta-diversity first appeared more than five decades ago, but there is still controversy over their precise meaning and application. Here, we focus on the concept of nestedness, the ordered loss of species along environmental or ecological gradients. Because there is no species replacement if the distribution of species among a number of sites is perfectly nested, some studies have defined nestedness as the inverse of species turnover. We argue that such a redefinition relies on a misinterpretation of the original concept of nestedness as the inverse of species replacement. Such a narrow interpretation might result in misleading conclusions about the mechanisms regulating species distribution patterns. We argue, in particular, that any quantification of nestedness must be as explicit as possible about the gradient to be analyzed.