Alfred Russel Wallace’s (1876) map of zoogeographical regions of the world was a milestone of 19th century biogeography. Based on the distributions and taxonomic relationships of mammalian families, Wallace’s classification became a foundation of modern biogeography. An international group of biogeographers, including Gary Graves (Division of Birds), recently published a next-generation map of Wallacean zoogeographic regions, incorporating phylogenetic and distributional data for >20,000 terrestrial vertebrate species. This study, published in Science (4 January 2013), is the first to combine evolutionary and distributional data for most living species of birds, mammals, and amphibians.
In 1876, Alfred Russel Wallace published the first map of global terrestrial zoogeographic regions based on the distribution and taxonomic relationships of mammalian families (Fig. 1). Wallace’s classification became a cornerstone of modern biogeography and a reference for biodiversity studies and conservation science. Wallace divided the world into six terrestrial zoogeographic units largely delineated by what we now know as the continental plates. Wallace’s original regionalization scheme implicitly considered ancestral relationships among species, but subsequent schemes during the past century generally used data only on the contemporary distributions of species without explicitly considering phylogenetic relationships.Google Earth application (kmz file) and a comprehensive summary of the analyses can be downloaded (pdf).
The Australian, Madagascan, and South American regions support the most phylogenetically distinctive assemblages of terrestrial vertebrates. These evolutionarily unique regions harbor radiations of species from several clades that are either restricted to a given region or found in only a few regions. The combined taxa map (Fig. 2) differs from previously published global zoogeographic maps derived exclusively from data on the distribution of vertebrate species. For example, central and eastern Siberia are phylogenetically more similar to the arctic parts of the Nearctic region than to other parts of the Palearctic. As a result, the newly defined Palearctic realm extends into the northern part of the Western Hemisphere.
The new classification of zoogeographic regions exhibits some interesting similarities with Wallace’s original classification, as well as some important differences. For example, Wallace classified islands east of Borneo and Bali in his Australian region, which is analogous to our Oceanian and Australian realms combined. In contrast, at least some of these islands (e.g., Sulawesi) belong to our Oriental realm, which spans Sundaland, Indochina, and India. Moreover, our Oceanian realm is separate from the Australian realm and includes New Guinea together with the Pacific islands, whereas Wallace lumped these two biogeographic units into the Australian region. The strait between Borneo and Sulawesi, now known as “Wallace’s Line,” was a major barrier to dispersal that greatly inhibited exchanges between the Australian and Asian land masses. Much debate subsequently arose regarding the precise location of the principal faunal divide between Wallace’s Oriental and Australian realms. Our analyses lend the strongest support to the hypothesis of Weber (1902), who positioned this boundary east of Sulawesi, corresponding to the zoogeographic boundary separating our Oriental and Oceanian realms. However, our taxon-specific geographic delineation for birds is more consistent with Wallace’s line than Weber’s.
The delineation of and relationships among our zoogeographic regions differ among taxa (Fig. 3). We found more distinctive regions for mammals (n = 34 regions) than for amphibians or birds (both n = 19 regions). A comparison of pβ matrices across the three vertebrate taxa revealed that amphibian assemblages located in the northeastern Arctico-Siberian, southern African, and Madagascan regions are more phylogenetically distinct than those of birds or mammals for the same regions. Moreover, the Australian region harbors more phylogenetically distinct assemblages of amphibians and mammals relative to birds.
The new delineation of the zoogeographic regions of the world appears robust to the type and quality of distributional and phylogenetic data used. Inclusion of additional phylogenetic information on branch length or improved resolution of the phylogenetic trees has the potential to facilitate a finer delineation of regions within realms. The inclusion of data (when they become available) on reptiles and invertebrates may also affect the boundaries of zoogeographic realms and regions. Nevertheless, the maps presented here delineate robust zoogeographic units for vertebrates that can be scaled within specific continents and/or taxonomic clades. Due to these qualities, our analytical approach and zoogeographic maps provide a baseline for a wide variety of comparative ecological, biogeographic, evolutionary, and conservation-based studies.
Ben G. Holt, Jean-Philippe Lessard, Michael K. Borregaard, Susanne A. Fritz, Miguel B. Araújo, Dimitar Dimitrov, Pierre-Henri Fabre, Catherine H. Graham, Gary R. Graves, Knud A. Jønsson, David Nogués-Bravo, Zhiheng Wang, Robert J. Whittaker, Jon Fjeldså, and Carsten Rahbek. 2013. An Update of Wallace's Zoogeographic Regions of the World Science 339 (6115), p74-78, published online 20 December 2012 (10.1126/science.1228282).