We revise concepts, definitions and examples of biogeographical transition zones to help develop a conceptual framework and differentiate them from other transitions that occur in the geographical space. A biogeographical transition zone is defined as a geographical area of overlap, with a gradient of replacement and partial segregation between biotic components (sets of taxa that share a similar geographical distribution as a product of a common history). It is an area where physical features, environmental conditions and ecological factors allow the mixture and the co‐occurrence of two or more biotic components, but also constrain their distribution further into one another. The biogeographical affinities of the taxa are the most fundamental information to consider to analyse biogeographical transition zones accurately. By plotting the frequency of different distribution patterns on maps, gradual changes in their relative contribution to a given area can be perceived. Thus, the most heterogeneous places in terms of distributional patterns can be defined numerically on strictly geographical grounds. Biogeographical transition zones can occur at every hierarchical level of a biogeographical regionalization as long as different biotic components come into contact geographically. Ecological boundaries or ecotones when characterized only by differences in dominance of some species, life forms or sets of characteristic species (not endemic) are not biogeographical transition zones as defined herein. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 113, 1–12.

The recognition of areas of endemism (AEs) is important for conservation biology and biogeographical regionalization. Our objective was to quantitatively identify AEs and distributional congruence patterns of native rodents at the tropical/temperate transition in the central Andes. We analysed 6200 geo-referenced distributional records of 80 species in north-western Argentina using NDM/VNDM software. We found 20 AEs defined by 22 endemic species (27% of the total rodent fauna) and 34 patterns of distributional congruence in non-endemic rodents. Geographical range congruence follows two main patterns running parallel along the Andes. One is related to the humid eastern slopes of the Andes (Argentinean Yungas forest) and the other to the high Andes (Argentinean Puna plateau). Endemism was mainly restricted to the southernmost part of the Yungas forest and adjacent dryer valleys (Monte desert). Species diversity was highest in the northern sector of the Argentinean Yungas forest, where several species reach their southern distributional range. This incongruence among hotspots of diversity and endemism has also been also noted in diversity studies at continental and global scales. Our results provide a starting point for conservation planning in the southernmost Central Andes, which combines the taper of tropical diversity and range-restricted species endemic to the tropical–temperate transition.Fil: Sandoval Salinas, Maria Leonor. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales E Instituto Miguel Lillo. Programa de Investigación de Biodiversidad Argentina; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Ferro, Luis Ignacio. Universidad Nacional Autónoma de México; México. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

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