Mammalian responses to Middle Holocene climatic change in the Great Basin of the western United States

In spite of decades of intense research directed toward understanding the climates and ecology of the Great Basin (western United States) during the past 10,000 years, the responses of mammals to the extreme aridity of the Middle Holocene (c. 8000-5000 years ago) in this region have been poorly understood. Using a well-dated small mammal sequence from Homestead Cave, north-central Utah, I show that the Middle Holocene small mammal faunas of this area underwent a decrease in species richness and evenness, driven largely by a series of local extinctions and near-extinctions coupled with a dramatic increase in the abundance of taxa well-adapted to xeric conditions. At the end of this period, some taxa that require relatively mesic habitats began to increase in abundance immediately, others did not rebound in abundance until several thousand years later, while still others have not returned at all. This suite of responses has been difficult to detect because climatic change at the beginning of the Middle Holocene was so much more substantial than that which occurred toward its end.