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

1. Detailed studies of population ecology are usually carried out in relati vely restricted areas in which emigration and immigration play a role. We u sed a modelling approach to explore the population consequences of such dis persal and applied ideas from our simulations to the conservation of wild b irds. 2. Our spatial model incorporates empirically derived variation in breeding output between habitats, density dependence and dispersal. The outputs ind icate that dispersal can have considerable consequences for population abun dance and distribution. The abundance of a species within a patch can be ma rkedly affected by the surrounding habitat matrix. 3. Dispersal between habitats may result in lower population densities at t he 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 th at 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 m etapopulations, dispersal into poorer quality territories may markedly redu ce total populations. 6. There are two main approaches to conservation: one is to concentrate on establishing and maintaining protected areas, while the ether involves cons ervation of the wider countryside. If dispersal is an important process the n protecting only isolated areas may be insufficient to maintain the popula tions within them.