Synchronous population fluctuations among geographically distant populations are ubiquitously observed and studied in many taxa, at distances of up to thousands of kilometers. This synchrony is known to be important for ecosystem functioning, for population rescue and extinction, and for the management of pests and diseases. However, the biogeography of synchrony – geographic patterns in the strength and nature of synchronous fluctuations – is little studied. A priori, synchrony may be stronger in some areas than others, or may occur on different timescales, or out to greater distances. Via novel applications of spatial statistics and new Fourier methods, we developed a worldwide biogeography of synchrony for the enhanced vegetation index (EVI) and for MODIS measurements of chlorophyll-a in the ocean; and we illuminated environmental causes of this biogeography.
Results/Conclusions
Patterns of synchrony for EVI and ocean chlorophyll have a pronounced biogeography, with some areas synchronized to very different degrees than others. Ocean chlorophyll synchrony is stronger in the centers of oceans, and at lower latitudes. EVI synchrony was strongest in southern Africa, Eastern Brazil, Northern Europe, Saharan Africa, and Australia. The biogeography of synchrony is timescale specific. For instance, ocean chlorophyll synchrony along the equator occurred almost exclusively on short timescales (<4 yrs), whereas Pacific Ocean synchrony away from the equator was primarily on long timescales (>4 yrs). EVI synchrony in the Sahara and on the Atlantic coast of Brazil occurred mostly on long timescales, whereas inland Brazilian synchrony had a larger short-timescale component. Formal comparison of the detailed biogeographies of synchrony of chlorophyll and EVI with those of potential environmental drivers via spatial statistics allowed us to identify Moran effects driving synchrony and its biogeography. Temperature and precipitation were primary Moran drivers, but other drivers were also involved, and Moran effects could be timescale dependent, or heterogeneous among continents or ocean basins. For some areas, temperature or precipitation synchrony drove nearly all of synchrony in EVI or chlorophyll, making it possible to produce scenarios of future synchrony in primary production as extensions of global circulation models.