Barn Swallow

Abstract

We develop an integrated population model (IPM) to study the demographic causes of synchrony in population dynamics, i.e., coincidence in the changes in demographic rates and of population growth in multiple populations. The model requires that component data sets are sampled at different sites and during time periods that must overlap at least partly. All data sets are analyzed within a single IPM that specifies process models that are structurally identical for all sites. The demographic rates are modeled with linear mixed models such that the spatio-temporal variance is decomposed into a common temporal variance and a site-specific temporal variance term. As a measure of synchrony, we use the intraclass correlation for each demographic rate computed as the ratio of the shared temporal variability to the total temporal variability. We estimate synchrony in the population growth rate in an additional step where we apply a linear mixed model to all posterior samples of the population growth rates, which themselves are based on the population size estimates in the main model fit as usual by Markov chain Monte Carlo methods. We apply this IPM to data sets of barn swallows ( Hirundo rustica ) collected at nine Swiss study sites over a total of 7-year period. We found strong synchrony in the probability of double brooding, weak synchrony in fledging success, and rather weak synchrony in the population growth rate; however, uncertainties due to the fairly short study duration were considerable. The concepts showcased in this chapter could also be extended to the modeling of multiple species at the same or at multiple sites, allowing the study of community synchrony.