Dispersal and connectivity in metapopulations

This paper reviews characteristics of dispersal that influence metapopulation functioning, such as releasing factors, density dependence, timing and types and health of dispersers. Economic thresholds, intraspecific conflicts and avoidance of inbreeding arc often regarded as the key ultimate or proximate (or both) causes of dispersal, but there is no consensus about the most important mechanisms. Dispersing individuals arc often considered to differ genetically from the residents but good supporting evidence has only been presented for some insect species. Sex and age differences in dispersal rates are most common in polygamous species and in long-lived species with many litters per female. A bimodal distribution of dispersal distances, earlier thought to be a common pattern, is probably an artifact, caused by habitat heterogeneity and varying survival of settled individuals. Dispersal distances are longer in poor environments. Habitat specialists are more affected by boundaries during dispersal than generalists. Dispersal just before or during the early reproductive season is common in certain species occupying early successional habitats. Dispersal increased both population and metapopulation size and persistence in plants, insects and small mammals.