Late-Holocene environmental conditions revealed by a small mammal assemblage in mountain areas of Northwestern Argentina

Based on a diverse Late-Holocene (1889-1743 cal yrs BP) small mammal assemblage (14 species, 204 individuals) resulting from the trophic activity of owls, we reconstruct the paleoenvironmental conditions of Las Chacritas area, Catamarca Province, northwestern Argentina. Twenty modern and one additional Late-Holocene samples from the region were used as comparative parameters in the paleoenvironmental reconstruction. Through direct comparison with a present-day assemblage from Las Chacritas, and using Nonmetric Multidimensional Scaling, spatial and temporal beta diversity (employing the Sorensen dissimilarity index), and the temporal beta diversity index (TBI) including all the small mammal samples, we quantitatively reconstruct the relationships among modern and Late-Holocene assemblages. Direct comparison showed significant differences, with relative abundances changing markedly over time, with several species of the Late-Holocene assemblage absent in the modern sample whereas many species frequent in the modern community absent in the Late-Holocene. NMDS analysis associated the Late-Holocene assemblage with modern samples of western drier environments. Beta diversity was low for presence-absence and moderate for abundance data, with higher contribution of turnover than nestedness, although for abundance data the proportion of nestedness was higher. TBI showed high variation among both Holocene sites and their present-day counterparts, whereas species gains dominated in modern samples. Our results suggest that the habitats surrounding Las Chacritas have modified markedly since the Late-Holocene. Presence of species today frequent in arid environments and absence of forest-dwelling species suggest that open, dry and relatively rocky habitats characterized this area in that interval.