Inter-population variation in demographic parameters: a neglected subject?

Demographic parameters and population growth rates vary among populations of the same species. Such variation can be extensive, as shown by a comparison of nine published studies of black-legged kittiwakes Rissa tridactyla. We argue that rather than being a nuisance, inter-population variation can improve our understanding of population dynamics. Analysis of data from several geographically dispersed studies can aid detection of causal relationships between demographic parameters and environmental factors and thus improve our understanding of impacts of e.g. climate change, and help elucidate mechanisms of population regulation. Extensive inter-population variation also adds another perspective to studies of life history evolution and should be taken into account in across-species comparisons.