Spatial synchrony of local populations has increased in association with the recent Northern Hemisphere climate trend

Abstract

According to ecological theory, populations whose dynamics are entrained by environmental correlation face increased extinction risk as environmental conditions become more synchronized spatially. This prediction is highly relevant to the study of ecological consequences of climate change. Recent empirical studies have indicated, for example, that large-scale climate synchronizes trophic interactions and population dynamics over broad spatial scales in freshwater and terrestrial systems. Here, we present an analysis of century-scale, spatially replicated data on local weather and the population dynamics of caribou in Greenland. Our results indicate that spatial autocorrelation in local weather has increased with large-scale climatic warming. This increase in spatial synchrony of environmental conditions has been matched, in turn, by an increase in the spatial synchrony of local caribou populations toward the end of the 20th century. Our results indicate that spatial synchrony in environmental conditions and the populations influenced by them are highly variable through time and can increase with climatic warming. We suggest that if future warming can increase population synchrony, it may also increase extinction risk.

Fig. 1.

Caribou population dynamics and response to NAO over two centuries in Greenland. (a) Dynamics of caribou populations, as indexed by fur trading and harvest data, between 1810 and 1981. Each color represents the same population in both periods. (b) Coefficients quantifying the strength of the NAO's influence on population dynamics in a plotted against the latitudes of these populations for the periods 1810–1865 (□) and 1910–1981 (○).

Fig. 2.

Variation in caribou population synchrony with temperature synchrony in Greenland. (a) Relation between pairwise population correlation for caribou populations Nuuk and Paamiut and pairwise temperature correlation for local winter temperatures measured at stations on the ranges of those populations, 1908–1981. Pairwise correlations were calculated for 25-year windows moved down each time series in 1-year steps. (r² = 0.64). (b) Indices of spatial synchrony of local winter temperatures (red) and caribou populations (blue) in western Greenland (see Materials and Methods). (c) Partial residual plot of the relationship between winter temperature synchrony and caribou spatial synchrony from the GAM. The solid line represents the nonlinear spline function, and the dashed lines are the 95% confidence intervals.

Fig. 3.

Relations between local temperature synchrony, winter temperatures, and the NAO in western Greenland. (a) Partial residual plot from the GAM of spatial synchrony of local winter temperatures as a function of mean winter temperature (in tenths of a degree Celsius) in western Greenland. (b) Relation between the winter NAO index and mean winter temperature in western Greenland; shown is the partial correlation plot from the multivariate generalized linear model (partial r² = 0.40) that also included Northern Hemisphere temperature anomalies and year. The solid line represents the nonlinear spline function, and the dashed lines are 95% confidence intervals.