Population dynamics in migratory networks
Migratory animals are comprised of a complex series of interconnected breeding and nonbreeding populations. Because individuals in any given population can arrive from a variety of sites the previous season, predicting how different populations will respond to environmental change can be challenging. In this study, we develop a population model composed of a network of breeding and wintering sites to show how habitat loss affects patterns of connectivity and species abundance. When the costs of migration are evenly distributed, habitat loss at a single site can increase the degree of connectivity (mixing) within the entire network, which then acts to buffer global populations from declines. However, the degree to which populations are buffered depends on where habitat loss occurs within the network: a site that has the potential to receive individuals from multiple populations in the opposite season will lead to smaller declines than a site that is more isolated. In other cases when there are equal costs of migration to two or more sites in the opposite season, habitat loss can result in some populations becoming segregated (disconnected) from the rest of the network. The geographic structure of the network can have a significant influence on relative population sizes of sites in the same season and can also affect the overall degree of mixing in the network, even when sites are of equal intrinsic quality. When a migratory network is widely spaced and migration costs are high, an equivalent habitat loss will lead to a larger decline in global population size than will occur in a network where the overall costs of migration are low. Our model provides an important foundation to test predictions related to habitat loss in real-world migratory networks and demonstrates that migratory networks will likely produce different dynamics from traditional metapopulations. Our results provide strong evidence that estimating population connectivity is a prerequisite for successfully predicting changes in migratory populations.
KeywordsHabitat loss Costs of migration Migratory animals Migratory connectivity
CMT was supported by the National Science Foundation under grant no. 0434642 and DRN was supported by a Discovery Grant from the Natural Sciences and Engineering Research Council of Canada.
- Alerstam T (1990) Bird migration. Cambridge University Press, CambridgeGoogle Scholar
- Berthold P (1998) Bird migration: genetic programs with high adaptability. Zoology 101:235–245Google Scholar
- Brewer D, Diamond A, Woodsworth EJ, Collins BT, Dunn EH (2000) Canadian atlas of bird banding. Canadian Wildlife Service, Environment Canada, OttawaGoogle Scholar
- Cramp S, Simmons KEL (eds) (1977) Handbook of the birds of Europe, the Middle East, and North Africa: the birds of the Western Palearctic. Oxford University Press, OxfordGoogle Scholar
- Gross JL (1999) Graph theory and its applications. CRC, Boca RatonGoogle Scholar
- Marra PP, Norris DR, Haig SM, Webster MS, Royle JA (2006) Migratory connectivity. In: Crooks KR, Sanjayan M (eds) Connectivity conservation. Cambridge University Press, New YorkGoogle Scholar
- Norris DR, Marra PP, Kyser TK, Royle JA, Bowen GJ, Ratcliffe LM (2006) Migratory connectivity of a widely distributed Neotropical–Nearctic migratory songbird. Ornithol Monogr 61:14–28Google Scholar