Small mammal endemism patterns in Northwestern Argentina

María Leonor Sandoval Salinas


Quantitative evaluations of species distributional congruence allow assessing previously proposed biogeographic regionalization and even identify undetected areas of endemism. The geographic scenary ofNorthwestern Argentinaoffers ideal conditions for the study of distributional patterns of species. In this paper we applied a grid-based explicit method in order to recognize Patterns of Distributional Congruence (PDCs) and Areas of Endemism (AEs), and the species (native but non-endemic and endemic, respectively) that determine them, in order to examine the relationships of small mammal species endemism with major environmental units. Also, we relate these distributional patterns to traditional biogeographic divisions of the study region and with a very recent phytogeographic study and we reconsider what we previously rejected as ‘spurious’ areas. Finally, we assessed the generality of the patterns found. The analysis resulted in 165 consensus areas, characterized by 7 species of marsupials, 28 species of bats, and 63 species of rodents. Twenty-five percent of the species that characterize consensus areas are endemic to the study region and define six AEs in strict sense while 12 PDCs are mainly defined by widely distributed species. While detailed quantitative analyses of plant species distribution data does not result in units that correspond to Cabrera’s phytogeographic divisions at this spatial scale, analyses of animal species distribution data does. We were able to identify previously unknown meaningful faunal patterns and more accurately define those already identified. We identify PDCs and AEs that conform Eastern Andean Slopes Patterns, Western High Andes Patterns, and Merged Eastern and Western Andean Slopes Patterns, some of which are re-interpreted at the light of known patterns of the endemic vascular flora. Endemism do not declines towards the south, but do declines towards the west of the study region. Peaks of endemism are found in the eastern Andean slopes inJujuyand Tucumán/Catamarca, and in the western Andean biomes in Tucumán/Catamarca. The principal habitat types for endemic small mammal species are the eastern humid Andean slopes. Notwithstanding, arid/semi-arid biomes and humid landscapes are represented by the same number of AEs. Rodent species define 15 of the 18 GPs, and only in one they have no participation at all. Clearly, at this spatial scale, non-flying mammals, particularly rodents, are bigeographically more valuable species than flying mammals (bat species).

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