Effects of population dynamics on genetics in mosaic landscapes

Most terrestrial landscapes consist of a mosaic of habitat patches of varying size and composition. This is perhaps most evident when the natural biome has been fragmented by human impact, as in the mixture of woodlots, cultivated fields and pastures so familiar to residents of eastern North America and northern Europe. One consequence of this patchwork of habitats is to subdivide many species into numerous localized collections of individuals. When an organism’s dispersal potential is limited relative to the dispersion pattern of the patches it can occupy, the landscape could be said to impose a population structure on the species. Here, a local population is being defined loosely as a collection of conspecifics more likely to interact with each other than with individuals from some other locality. The range of possible population structures can be described as a continuum, with highly interdependent populations connected by high rates of migration lying at one extreme and highly isolated, independent populations lying at the other. The way in which a particular landscape imposes a population structure depends on the movement ecology of the species in question, as well as on the spatial arrangement of patch types (Chapter 7). For example, the same landscape could impose very different population structures on snails and sparrows.