Spatial patterns of demography and genetic processes across the species\u27 range: Null hypotheses for landscape conservation genetics

Compared with populations near the core of a species\u27 range, edge populations tend to be characterized by low density and high temporal variation. Based on empirical studies quantifying this pattern, we show that effective population size (Ne) could be 2 to 30 times greater near the core of the species\u27 range than near the edge of the range. Hence, the rate of genetic drift may be 2 to 30 times greater near the edge of the range. Despite these strong spatial patterns in Ne, empirical findings indicate that peripheral populations sometimes have less but sometimes have more genetic diversity than core populations. Our analysis indicates that this variation can be explained by uncertainty in spatial patterns of migration rates. Nevertheless, our analysis: (1) provides a framework or null hypothesis for empirically assessing how spatial patterns of migration or selection influence large-scale spatial patterns of genetic diversity, (2) highlights the potential importance of contemporary processes, such as spatial patterns in Ne (cf. historical phenomena, such as range expansion) in the development and maintenance of large-scale spatial patterns in genetic diversity, and (3) provides new context for understanding the conservation value and vulnerability of peripheral populations. The conservation of ecological/evolutionary processes requires understanding large scale spatial patterns of demographic and genetic processes such as that described here