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For a long time people thought that living organisms were created in ‘centres of origin’ or creation spots, from which they moved towards the most diverse areas of the planet. In this way, people explained why kangaroos exist only in Australia, why lions are exclusive of Africa or why the highest diversity of pines is found in North America. Nonetheless, we now understand that species originate in a very different way. Charles Darwin, one of the most prominent naturalists, was interested in understanding how species originated. The presence of ostriches in Africa and that of other very similar birds in South America, the rheas, drew his attention. He reasoned that if these birds were related, then, could South America and Africa be related? The theory of continental drift and the movement of the tectonic plates gave the answer. Life and earth evolve together. Nowadays, biogeography is the result of the integration of several areas of science, such as evolution, geography and palaeontology. This multidisciplinary approach allows us to understand the distribution of living organisms on the planet.
In 1858 Sclater, and later Wallace (1876), divided the world in several biological regions, which were characterised by the biota they contained. In 1920, Augustin de Candolle divided the world in 20 regions, which represented the different plants on the planet. Natural barriers, such as oceans, deserts, temperature changes and ecological barriers, demarcated these regions. In this way, the planet was divided into biogeographic regions that can potentially explain the distribution of current and extinct taxa. These regions also reflect the history of the planet, told by the biota itself.
Very interestingly, Mexico seems to be the point where two types of biota diverge: the Nearctic and the Neotropic ecozones. This area of divergence was recognised by Halffter (1962) as the Mexican zone of transition. This zone exhibits a hybridisation of the biological components of both ecozones.
Therefore, if taxa have similar distributions, one can say that they have been subjected to the same historical patterns of dispersion, so that their current distribution is the result of common histories. This is fundamental in order to understand the resulting geographic space used by the biota and is the focus of the research of Miguel Rivas Soto, a current student at the spatial analyses laboratory, at the Institute for Biology, of the National Autonomous University of Mexico. Miguel is using the distribution of several beetle taxa (Scarabaeidae) used by Halffter (1962) himself, in order to test and demonstrate the limits of the biotic regionalisation on Central- and North America. Miguel is also testing how the hypotheses of spatial homology of beetles can be contrasted and compared to those proposed for other taxa.
Biogeographic studies are important, not only because they can account for the history of the planet, as told by living organisms, but because they can explain the occurrence of some of the biological diversity of a given region. It gives us the historical tools that we need in order to implement conservation areas, biological corridors or to plan a sustainable use of natural resources. The more taxa is used to test these hypotheses, the more we will be closer to answer the ‘what, when and where’ questions on the planet’s biodiversity; we will be more prepared when facing the global biodiversity’s crisis, caused by overexploitation, demographic growth and global weather change.
