SPATIAL ASYNCHRONY AND PERIODIC TRAVELING WAVES IN CYCLIC POPULATIONSOF FIELD VOLES

We demonstrate evidence for the presence of travelling waves in a cycl ic population of field voles in northern Britain by fitting simple, em pirical models to spatially referenced time series data. Population cy cles were broadly synchronous at all sites, but use of Mantel correlat ions suggested a strong spatial pattern along one axis at a projection line 72 degrees from North. We then fitted a generalized additive mod el to log population density assuming a fixed-form travelling wave in one spatial dimension for which the density at each site was offset in time by a constant amount from a standard density-time curve. We assu med that the magnitude of this offset would be proportional to the spa tial separation between any given site and the centroid of the samplin g sites, where separation is the distance between sites in a fixed dir ection. After fitting this model, we estimated that the wave moved at an average speed of 19 km yr(-1) heading from West to East at an angle of 78 degrees from North. Nomadic avian predators which could synchro nize populations over large areas are scarce and the travelling wave m ay be caused by density-dependent dispersal by field voles and/or pred ation by weasels, both of which act at a suitably small spatial scale.