COS 42-5
Global beta-diversity is more sensitive to loss of species with small versus large ranges

Tuesday, August 11, 2015: 2:50 PM
319, Baltimore Convention Center
Joshua Ladau, Gladstone Institutes, University of California San Francisco, San Francisco, CA
Jessica Green, Center for Ecology and Evolutionary Biology, University of Oregon, Eugene, OR
Katherine S. Pollard, Gladstone Institutes, University of California San Francisco, San Francisco, CA

Beta-diversity -- broadly defined as the variability of communities between locations -- can promote multiple ecosystem functions, insure against loss of function in communities, and impart ecosystem stability. Thus, understanding how beta-diversity will be impacted by ongoing extinction events is of high importance. Previous studies have shown that beta-diversity is more strongly correlated with the distributions of wide-ranged and abundant species than narrow-ranged and rare species. These observations suggest that beta-diversity will be impacted relatively little by incipient extinctions of threatened species, which tend to have narrow ranges and are rare. To investigate this hypothesis, we (i) use a database of the global distributions of almost all known amphibian, bird, and mammal species to empirically assess the relative impacts of extinctions on four classic measures of beta-diversity and (ii) develop a mathematical theory based on geometric probability to understand and predict these impacts.


Contrary to expectations, we find empirically that at global scales beta-diversity is more strongly impacted by extinctions of narrow-ranged species than wide-ranged species. As measured by the change in beta-diversity per species lost, the impacts can be over 1000 times greater for loss of narrow-ranged species than wide-ranged species. This sensitivity to extinctions of narrow-ranged species is evident across all of the taxa that we examined, and for all measures of beta-diversity and in almost all geographic regions that we examined. Our mathematical theory is highly predictive of these empirical observations, and it makes additional predictions about the relationships between beta-diversity and geometric properties of ranges, which we confirm, suggesting that the differential impacts of extinctions on beta-diversity stem from fundamental geometric constraints. Our results show that because loss of narrow-ranged species has an inordinate influence on beta-diversity, incipient extinctions of narrow-ranged species will disproportionately affect beta-diversity, with likely ramifications for the ecosystem services and functions provided by beta-diversity.