Spatial synchrony of a threatened shorebird: Regional roles of climate, dispersal and management

Correlated climate patterns, dispersal, and similar management practices may synchronise dynamics of populations in close proximity, which tends to reduce metapopulation persistence. However, synchronising and desynchronising mechanisms can act at multiple spatial scales, which means that for wide-ranging species, patterns of spatial synchrony and their causes might vary across the species' range. We examined the relationships of spatial autocorrelation in winter climate, dispersal distance and predator management to the spatio-temporal dynamics of the Western Snowy Plover Charadrius nivosus nivosus, a threatened shorebird that breeds along the Pacific coast of the United States. We investigated how signals and drivers of plover population growth dynamics vary among populations occupying northern, central, and southern regions of the species' U.S. range. Across the metapopulation and specifically the core of the species' range in the south, we found that plover populations within 132 km of each other exhibited detectable levels of synchrony, which fell within published estimates of dispersal distance. Furthermore, similar predator management among sites increased the degree to which nearby populations were synchronised. There was, however, no evidence of spatial synchrony in populations of the northern and central regions. Regional differences in synchrony were associated with different population drivers and structure; prolonged cold periods had the strongest influence on the growth of northern populations while predator management had the strongest influence on southern populations. Northern populations were also smaller than the south, which likely reduced our ability to detect spatial synchrony because of increased demographic stochasticity. Neither climatic nor management variables had a detectable influence on central populations. Although the primary objective of threatened and endangered species management is to increase populations to viable levels, we recommend that conservation biologists and land managers acknowledge region-specific processes when considering the long-term persistence of wide-ranging species and coordinate inter-agency efforts to manage neighbouring populations effectively.