Consequences of large-scale processes for the conservation of bird populations

1. Detailed studies of population ecology are usually carried out in relatively restricted areas in which emigration and immigration play a role. We used a modelling approach to explore the population consequences of such dispersal and applied ideas from our simulations to the conservation of wild birds. 2. Our spatial model incorporates empirically derived variation in breeding output between habitats, density dependence and dispersal. The outputs indicate that dispersal can have considerable consequences for population abundance and distribution. The abundance of a species within a patch can be markedly affected by the surrounding habitat matrix. 3. Dispersal between habitats may result in lower population densities at the edge of good quality habitat blocks and could partially explain why some species are restricted to large habitat fragments. 4. Habitat deterioration may not only lead to population declines within that habitat but also in adjacent habitats of good quality. This may confound studies attempting to diagnose population declines. 5. Although mobile species have the advantages of colonizing sites within metapopulations, dispersal into poorer quality territories may markedly reduce total populations. 6. There are two main approaches to conservation: one is to concentrate on establishing and maintaining protected areas, while the ether involves conservation of the wider countryside. If dispersal is an important process then protecting only isolated areas may be insufficient to maintain the populations within them.