Spatially synchronous population dynamics: An indicator of Pleistocene faunal response to large-scale environmental change in the Holocene

Investigation of the population dynamics of animal species that survived the rapid climatic warming that marked the Pleistocene-Holocene transition may provide insight into the manner in which they will respond to future climate change. Among the large mammalian fauna that persisted in the far north following the warming at the end of the Pleistocene, caribou and wild reindeer have only recently become the focus of studies of population response to contemporary climate change. Here, we present analyses of the dynamics of multiple populations of Greenlandic caribou and Russian wild reindeer (both Rangifer tarandus) in relation to large-scale climatic fluctuation, the North Atlantic Oscillation (NAO). These populations, separated by a minimum of 3300 km and a maximum of 7500 km, displayed in some instances nearly perfectly synchronous dynamics, despite a lack of shared predators or opportunities for mixing. Non-linear statistical modeling indicated that the degree of synchrony among Greenlandic and Russian populations was a function of the strength of the influence of the NAO on the dynamics of these populations: populations influenced similarly by the NAO tended to be more synchronized in their dynamics, and vice versa. Moreover, the NAO influenced some populations positively and others negatively, indicating that responses to further changes in the NAO may not be consistent within this species throughout its distribution. Nonetheless, these results, together with those of other studies, indicate that this species-which has been of considerable importance to human settlement of the far north-is influenced by large-scale climatic change throughout its circumpolar distribution.