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Dispersal Models General – Module B2 Spatial Modelling in Ecology, 5 ECTS – – – – Develop programming skills Implement, apply and critically assess computer models Understand the role of spatial processes for ecosystem dynamics Confronting models with data Aims Content Implement, apply and critically assess computer models Importance of dispersal for migration and population persistence Approaches to modelling dispersal: Long-distance dispersal Fitting dispersal models to data Individual-based (e.g. random walk) Dispersal kernels (e.g. diffusion) Network approaches Methods – – Computer exercises - Programming (R language) - (group work) Literature study – Essay/report (8-12 pages incl. figures) Exam Time and Place Mo: 10:00-13:00 (S 123); We.: 14:00-19:00; Fr.: 09:00-12:00, S22 (GEO) (Jan 7 – Feb 8 2009) Overview • What is dispersal? • How does dispersal affect the spatial distribution of populations? – Metapopulation models Some terminology • Dispersal: The movement away from an existing population or away from the parent organism • Colonization: The foundation of a new population as a consequence of the dispersal of offspring to an unoccupied site, and the subsequent establishment of a population in this site. • Migration: The spread of a species into a region that previously was not part of its range Wikipedia, Biological dispersal Schurr, Frank (2005), PhD thesis, p. 2 Why dispersal matters • The dynamics of populations depends on the four demographic processes of birth, death, immigration and emigration. • This 'fact of life' defines - in the words of Begon, Harper and Townsend (1996) - 'the main aim of ecology: to describe, explain and understand the distribution and abundance of organisms'. • Dispersal determines two of the four demographic processes, namely immigration and emigration. Schurr, Frank (2005), PhD thesis, p. 1 Benefits of dispersal • Offspring survival is often (but not always) higher away from the parent (densitydependent predation or pathogens; competition with adults) • Reach favourable habitats (directed dispersal) • Colonize new habitats or regions (risk spreading) Costs of dispersal • Dispersal mortality • Reach less favourable habitats • Reduced local density (and competitiveness) Examples of dispersal • Seed dispersal – Wind, animals (fur, intestines), water, active selfdispersal (Impatiens spp.) • Dispersal across land surface (when continents where still together) • Animals „running, flying“ • Passive dispersal in animals: spiders (wind) Dispersal and the spatial distribution of species Glanville fritillary butterfly on Åland Islands (SW Finland) http://www.helsinki.fi/science/metapop/Field_sites/Aland.htm