Dramatic recent changes in small mammal assemblages from Northern Patagonia: A caution for paleoenvironmental reconstructions

Abstract

Temporal differences in fossil assemblages of small mammals can generate important insights into associated environmental conditions. Moreover, byincluding modern assemblages in such comparisons, it may also be possible to identify the effects of recent human colonization on mammal communitiesand their habitats. To explore potential signals of European colonization in northwestern Patagonia, we compared fossil and modern assemblages ofsmall mammals from two newly characterized paleontological sites in the Limay Valley region of Río Negro Province, Argentina. The material analyzedconsisted of 18 species of small-bodied terrestrial mammals identified from a sample of 27,992 specimens. Fossil assemblages dating from 6453 to 1002calibrated years before present were relatively stable in taxonomic composition and displayed only minor differences in relative species abundances. Incontrast, the modern assemblages examined were clearly distinct, containing a different suite of numerically dominant taxa and lacking three previouslyabundant grassland species that are presumed to have gone extinct in the vicinity of our study sites. We suggest that these changes reflect substantialpost-colonization modifications of surrounding landscapes, including establishment of pine plantations, changes in fire regimes, and introductions oflivestock and invasive species of plants. If correct, this supposition raises important concerns regarding the use of modern assemblages as a baseline forreconstructing paleoenvironmental conditions. To avoid potential misinterpretations associated with the use of modern faunal assemblages, we suggesttwo potential alternative strategies for inferring temporal changes in environmental conditions.