Universal scaling of beta-diversity across taxa and terrestrial and marine ecosystems

Background/Question/Methods

Characterizing and understanding geographic patterns of biodiversity is fundamental to ecology: geographic patterns of biodiversity are used to develop ecological theory, establish conservation priorities, and manage ecosystem services.   That useful geographic patterns of biodiversity exist is a direct consequence of spatial turnover of ecological communities, or beta-diversity.  Thus beta-diversity occupies a central position in ecology.  Despite its importance, the drivers of beta-diversity are just beginning to be studied and no universal laws of beta-diversity are documented.   Here, we show how beta-diversity is determined by the shapes of species ranges at a global scale, and that this scaling between beta-diversity and shapes of ranges is universal for all described amphibians, birds, and mammals.

Results/Conclusions

Using IUCN range maps of all described amphibian, bird, and mammal species, we observed that a fundamental component of beta-diversity, the number of species occurring in exactly one a pair of sampling locations, depends linearly on the total perimeter of species ranges with a scale factor of approximately 0.6 for all three sets of species and across terrestrial and  marine ecosystems.  We also observed that key measures of beta-diversity, the Sorenson and Jaccard indexes, depend linearly on the ratio of the mean range perimeter to range area, with universal scale factors of approximately 0.3 and 0.6, respectively across these same taxa and ecosystems.  We develop a theory using geometric probability that predicts that these scale factors are 2/π=0.6366, 1/π=0.3183, and 2/π=0.6366, respectively.   The theory shows that the universal scaling likely arises from universal features of species ranges and fundamental properties of geometric translations.  These findings suggest that ecological processes act on beta diversity via effects on range shapes, and that the actions are governed by remarkably simple, yet not immediately obvious, rules.  The linkages additionally suggest unrecognized conservation value in regions of high beta-diversity because threatened species tend to persist near range boundaries.