Paula C. Dias, Jacques Blondel & Marcel M. Lambrechts

Dias, P.C., Blondel, J. & Lambrechts, M.M. 1999. Consequences of source-sink dynamics for passerine populations. In: Adams, N.J. & Slotow, R.H. (eds) Proc. 22 Int. Ornithol. Congr., Durban: 2967. Johannesburg: BirdLife South Africa

Habitat heterogeneity can affect the functioning of local populations, both from ecological and evolutionary points of view. Spatial differences in habitat quality are often associated with demographic differences. For a given species, a local demographic excess arises in good quality habitats (‘sources’), whereas lower quality habitats (‘sinks’) yield a demographic deficit. Within a landscape, permanent migration from sources to sinks may stabilise the overall demographic system. This situation requires a rethinking of some classical concepts such as niche and carrying capacity, and it can explain the persistence of local maladaptation, and improve conservation practice. The evolutionary stability of a source-sink system relies on the absence of adaptive evolution in sinks. The genetic processes occurring in source-sink systems remain to be fully explored, but sink populations probably contribute little to the genetic future of the species. The representation of the population dynamics of a species by source and sink habitats connected by asymmetric migration (mainly from source to sink) has received empirical support for a number of species. Multi-species implications of the source-sink concept are also being studied, and these promise an enhanced understanding of the determinants of community richness.