The zoogeographical domains: a new conservation target at global scale

Zooregions are classifications of the Earth’s surface based on characteristic species assemblages. Consequently, zooregions reflect how ecological, evolutionary, and historical processes have been acting over millions of years, arguably making them the largest entities to conserve the uniqueness of the species assemblages on Earth. Because species are distributed along zooregions heterogeneously, to conserve zooregions adequately, we need to protect their characteristic areas (transition, core or endemic areas), what we call the zoogeographical domains. Here we propose a method to characterize the zoogeographical domains basing on four metrics, which are independently used in macroecological and biogeographical studies but have not been considered in combination before. These metrics are: (i) species turnover index, (ii) regional relative richness index, (iii) a species endemism index, and (iv) a species occupancy level index. To calculate these indexes, we used the delineation of the zooregions and the distribution of the characteristic and non-characteristic species within each zooregion. Then we used clustering methods to aggregate geographical areas with similar characteristics and defined the optimal number of zoogeographical domains using piecewise regression. We applied the proposed method to identify zoogeographical domains in mammals revealing seven distinct domains: four describing diverse types of core-endemic areas, and three describing diverse types of transitional areas. Additional analyses show how human impact and protected areas are heterogeneously distributed among these seven zoogeographical domains, what suggests an unbalanced protection of the species assemblages. Our approach offers a new conceptual framework to characterize the largest forms of organization on Earth and identify concrete targets to ensure the uniqueness of biodiversity at global scale.