The checkered landscapes of the Dorset Heathlands demonstrate that the world is a patchy place (see Figure 9.7).

The patchy nature of the landscape ensures that for many species, areas of suitable habitat do not cover large, continuous regions, but rather exist as a series of favorable sites that are spatially isolated from one another.

refers to a population of populations, but it is usually defined in a more particular sense as a set of spatially isolated populations linked to one another by dispersal (FIGURE 9.15). In some metapopulations, certain populations are sources (from which the number of individuals that disperse to other populations is greater than the number of migrants they receive) while other populations are sinks (which receive more immigrants than the number of emigrants they produce).

FIGURE 9.15 TheMetapopulationConcept A metapopulation is a set of spatially isolated populations linked by dispersal. (A) Seven patches of suitable habitat for a species are diagrammed, four of which are currently occupied and three of which are not. The area outside of these seven patches represents unsuitable habitat. (B) Satellite image of a group of lakes in northern Alaska that are sometimes connected to one another by temporary streams that form after the snow melts or after periods of heavy rainfall. View larger image