Distinguishing the effects of the Red Queen and Court Jester on Meiocene mammal evolution in the northern Rocky Mountains

Red Queen hypotheses maintain that biotic interactions are the must importa nt drivers of evolutionary change, whereas Court Jester hypotheses regard p hysical-environmental perturbations, such as climate change, as most import ant. Tests for the biotic effects of climate change that are conducted on t oo large a geographic scale can falsely reject the Court Jester because cli mate is so complex its manifestation is in opposite directions in different geographic areas. Consequently, faunal responses vary from place to place, and lumping of data from different climate zones averages out any local fa unal responses. Likewise, tests that are conducted at inappropriate tempora l scales will not be effective at distinguishing between the Red Queen and Court Jester. A test at a temporal and geographic scale that takes the above consideratio ns into account suggests a biotic response of mammals to a climatic warming event in the northern Rocky Mountains 18.5-14.0 Ma (the late-Early Miocene climatic optimum). During the environmental perturbation, mammalian specie s richness possibly increased, faunal turnover was pronounced, and taxa ada pted to warm, arid environments became mon abundant in numbers of species a nd density of individuals. The data are consistent with environmental chang e-the Court Jester-driving evolutionary change at sub-continental spacial s cales and temporal scales that exceed typical Milankovitch oscillations. Th e Red Queen may be active at smaller temporal and geographic scales.