The distribution of all animals on earth has been shaped by a combination of changing temperature, the rise of mountains, and shifting plate tectonics, reports a paper published online this week in Nature Ecology & Evolution. The study identifies clear boundaries that separate groups of mammals, birds and amphibians into different regions of the world, with more evolutionarily distinct groups found in areas separated by major geological events, and closely related groups separated by more recent climatic change.
Similar types of animals tend to occur together in the same areas of the world, known as biogeographical regions. For example, the Wallace Line recognizes a sharp boundary running through Indonesia with groups of animals on either side more closely resembling those found in either Australia or Asia. However, the forces that shape these boundaries across the globe have not previously been investigated.
In this study, Gentile Francesco Ficetola and colleagues compare the distribution of the world's land-based biogeographical regions to models of climate variation, mountain building, and tectonic movement, in order to evaluate the extent to which each of these factors may have created barriers to the movement of animals. They find that the deepest evolutionary divergences are found between neighbouring areas subjected to a combination of all three processes. For example, when the African, Asian, Arabian and Eurasian continental plates collided within the past 100 million years, major mountain chains like the Himalayas were formed, changing the regional climate and forming sharp divisions across the Old World. In contrast, the evolutionary relatedness of animal groupings found in North America, as well as those found in eastern Asia, are found to be unrelated to any tectonic activity, and most likely reflect preferences for different climatic conditions across these continents.
In an accompanying News & Views article, Alexandre Antonelli writes: “Naturalists have long documented major differences in the fauna and flora of different landmasses and regions… However, explaining these differences has often relied on untested hypotheses… Ficetola et al. present an explicit test of the main factors suggested to underlie the boundaries of the world’s terrestrial bioregions.”