Synchrony in metapopulations at multiple time scales: theory, experiments, and field data

Research context: Populations of the same species in locations hundreds of kilometers apart often fluctuate in unison or partly in unison, a phenomenon called synchrony. For instance, British aphid species, of economic importance because they are a major agricultural pest, outbreak 80% in synchrony over short distances and 50% in synchrony over distances of 200km, a huge distance for most aphid species. In fact, synchrony is widespread, and has been detected in birds, lemmings, fish such as cod, human pathogens such as measles, amphibians, and numerous other species. Many species exhibiting synchrony are of major conservation, economic, or health importance. Population synchrony has practical importance for several reasons. For instance, synchronized pest or disease populations require a coordinated response. An endangered species whose populations are synchronized is in accentuated danger of final extinction because populations are simultaneously low and might all go extinct by chance at once. An exploited synchronized species is periodically unavailable or less available across a wide area in many markets. Synchrony has been measured with methods that characterize the degree of synchrony between two populations only by a single number from 1 (perfect synchrony) down to -1 (perfect asynchrony). This approach is useful but limited: our results show synchrony is too complex to be captured with one number. Synchrony between two populations can occur mainly on short time scales, with little to no synchrony on long time scales; or on long time scales, with little or no synchrony on short time scales; or on any range of time scales. Synchrony between environmental variables in different locations has the same complexity. For instance, temperatures in London and Glasgow rise and fall largely together on annual time scales (seasonal variation) and multi-annual time scales (the North Atlantic Oscillation), but short-time-scale (day-to-day) temperature variation in London may resemble that in Glasgow much less. Different time scales of synchrony have different ecological and extinction-risk implications, and may have different implications for optimal control strategies for pests. In addition, new and important preliminary results show that the time-scale-specific structure of environmental synchrony is changing as part of climate change, and likely affects population synchrony, and thereby extinction risk. Research aims: We will use large spatio-temporal databases, new theory, and new lab experiments to obtain a broad time-scale-specific description of environmental and population synchrony, and to assess the implications of observed patterns for climate change, extinction risks, and inference of what mechanisms cause synchrony in the field. Applications: We will provide information about a newly observed and previously unrecognized aspect of climate change and a global assessment of its overarching importance for conservation and pest management applications and for ecological understanding.