Where does environmental stochasticity most influence population dynamics ? An assessment along a regional core-periphery gradient for prairie breeding ducks / Richard E. Feldman, Michael G. Anderson, David W. Howerter, and Dennis L. Murray.

Includes bibliographical references (pages 902-903).

Aim Geographical disparities in the effect of the environment on population
dynamics have been shown to follow a core-periphery gradient when peripheral
populations are less abundant and occur in marginal habitat.Whether the gradient
in environmental influence occurs in the absence of a gradient in abundance is not
known.We tested whether duck populations on the periphery of their main breeding
region were more strongly affected by environmental stochasticity and less
abundant than at the core.
Location The Prairie Pothole Region of central United States and Canada
Methods We used the North American Waterfowl Breeding Population and
Habitat Survey to model the dynamics of 10 duck species at 1059 sites spanning
1961–2012.We used the North American Breeding Bird Survey to measure abundance
at the same sites, averaged over the same time span. We used structural
equation models to characterize relationships among a site’s distance from the
regional centre, a site’s abundance, and the degree to which a site’s ducks were
affected by environmental stochasticity.
Results Environmental stochasticity never strongly contributed to population
dynamics in the region’s core. However, we did not find a linear increase in environmental
stochasticity with increasing distance from the core. For seven species,
we found that environmental stochasticty was stronger in sites of lower abundance.
For only two species did average abundance decline from the region’s core to
periphery.
Main conclusions Variability in the magnitude of environmental stochasticity
follows coarse spatial differences in wetland productivity. Yet, among peripheral
sites, the contribution of the environment to population dynamics varies, possibly
reflecting the importance of the local environment and dispersal.