Decline of Mammal Species Diversity Along the Yungas Forest of Argentina

OJEDA, R. A.; BARQUEZ, R. M.; J. STADLER; R. BRANDL

BIOTROPICA

BlackWell Publishing Inc

Lugar: Zürich 8092, Switzerland; Año: 2008 vol. 40 p. 515 - 521

0006-3606

The southernmost extension of tropical Andean–Amazonian forests protrudes into the arid to semiarid habitats in northwestern Argentina. We analyzed the declineof species richness of forest mammals along these Yungas forests. In particular, we tested whether species decline is due to a general latitudinal effect and whether thedrop of species from the assemblages was independent from species’ traits and environmental variables. For these tests, we estimated the geographic range edges of 39species of forest mammal and estimated the species richness with bands of 30. First, we compared the slope of the decline of species richness from north to south(5.8 species/degree) with the decline expected from the latitudinal species gradient (1–3 species/degree). The decline in species richness of forest mammals along theYungas was significantly steeper than expected. Second, with a null model assuming a random drop of mammal species we derived confidence limits for the expected species richness and number of range edges within the bands. None of the forest mammals reached the tip of the forest, in marked contrast to nonforest mammals. More range edges than expected from the null model fell within the bands 23◦30–24◦00 S and a band near the tip of the Yungas indicating a nonrandom drop of species. The correlation between vulnerability traits and range edges suggests that processes associated with the availability of resources influence the drop of species.We propose that a suite of macroecological attributes interacting with a decrease in habitat quality determines the pattern of species richness in the Yungas forest.