I DEA AND PERSPECT IVE Navigating the multiple meanings of b diversity: a roadmap for the practicing ecologist

Marti J. Anderson,* Thomas O. Crist, Jonathan M. Chase, Mark Vellend, Brian D. Inouye, Amy L. Freestone, Nathan J. Sanders, Howard V. Cornell, Liza S. Comita, Kendi F. Davies, Susan P. Harrison, Nathan J. B. Kraft, James C. Stegen and Nathan G. Swenson Abstract A recent increase in studies of b diversity has yielded a confusing array of concepts, measures and methods. Here, we provide a roadmap of the most widely used and ecologically relevant approaches for analysis through a series of mission statements. We distinguish two types of b diversity: directional turnover along a gradient vs. nondirectional variation. Different measures emphasize different properties of ecological data. Such properties include the degree of emphasis on presence ⁄ absence vs. relative abundance information and the inclusion vs. exclusion of joint absences. Judicious use of multiple measures in concert can uncover the underlying nature of patterns in b diversity for a given dataset. A case study of Indonesian coral assemblages shows the utility of a multi-faceted approach. We advocate careful consideration of relevant questions, matched by appropriate analyses. The rigorous application of null models will also help to reveal potential processes driving observed patterns in b diversity.