Abstract
THE last two or three decades have witnessed great progress in the studies of ecological and geological factors of distribution of plants and animals, but the results of these studies have had little influence on biogeographers, whose work is still mainly concerned in the parcelling out of the globe's surface into regions, provinces, etc., characterized by statistical ratios of endemic forms and those common to several divisions. The methods of biogeographical work remain generally the same as in the time of Wallace, and a great proportion of literature (zoogeographical in particular) is devoted to discussions of the exact boundaries between formal divisions. When, however, two types of fauna or flora, different in their geological origin and adjusted to different ecological conditions, have to develop in close geographical proximity, there can be no linear boundary between them. Their various elements will penetrate more or less deeply into the main area occupied by the other type, this process being usually favoured in the case of one of the types by slow climatic changes in a certain direction. When such changes, for example, favour the spread of forests over a steppe area, some ‘islands' of steppe with their characteristic plant and animal population will still remain as evidence of former conditions. Usually, in calculating statistical ratios, such inclusions of alien fauna, or flora, are not distinguished from the elements of the dominating population, which is obviously incorrect.
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UVAROV, B. A New Method in Biogeography. Nature 139, 492–494 (1937). https://doi.org/10.1038/139492a0
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DOI: https://doi.org/10.1038/139492a0