La búsqueda del centro de origen en Biogeografía Histórica

Abstract

We study the application of the concept ‘centre of origin’ in Historical Biogeography through the predictions of a commonly used biogeographic model, here defined as “symmetric model”: i) local appearance of new species, followed by ii) expansion of the range of the distribution area of the new species. The first prediction occurs only in island species: a) the local appearance of new species has not been documented in not insular regions; b) the centre of origin cannot be accurately located for not insular species, and c) the criteria for infer it do not converge. The second prediction applies only for invasive species, after opening pre-existent barriers, showing their intrinsic capacity for linear expansion of the area at approximately constant speed and not controlled by external factors. The symmetric model assumes a symmetrical biogeographic dynamics: 1st) local origin, 2nd) gradual expansion, 3rd) stasis, 4th) gradual contraction and 5th) extinction. Diverse data refute this symmetrical model: a) the endemic species, the only ones who have a local distribution, show incapacity for expansion of their area; b) the “taxon cycle” in insular species shows that the area of the colonizing species always tend to decrease while differentiation occurs; c) the entries and exits of the guide species in the fossil record show an asymmetric pattern, with very rapid, quasi-synchronic appearance at regional scale and very slow, diachronic extinction along their distribution area; and d) the chronological asymmetry of the paleobiogeographic history of taxa, showing a wide distribution area at the beginning and a slow trend towards area contraction and fragmentation at the end, before extinction. Therefore, the data refute the applicability of the centre of origin concept and point to an asymmetric model of biogeographic dynamics: 1st) sudden appearance of the taxon in a wide area, 2nd) stasis, 3rd) slow contraction and 4th) extinction, frequently after previous fragmentation of the area.