4.4 The relationship between Ne and genetic diversity
According to the neutral model (Kimura, 1983), larger populations are expected to exhibit greater levels of genetic diversity than smaller ones. However, empirical support for this theory has been conflicting. Some studies report a correlation between population size and diversity (Aho et al., 2006; Hague & Routman, 2016; Knaepkens et al., 2004) while others fail to do so (Bazin et al., 2006; Lonsinger et al., 2018). The present results are generally in line with the neutral model (Figure 6a). The variation is large, however, and in some meta­populations we find no correlation between N e and the level of heterozygosity Figure 6a).
There is no apparent correlation between expected retention of heterozygosity over 100 years and N e (Figure 6b). Most of this lack of correlation is explained by the fact that heterozygosity is increasing in many of the populations monitored. The increase is likely due to genetic connectivity among populations with systems, and can also be due to connectivity with populations that we have not been able to detect in this screening. When considering only populations where heterozygosity is observed to decrease over the 40-year monitoring period we find a pattern which appears relatively consistent with expectations, i.e., that populations with highN e tend to exhibit a higher degree of retention of H E (Figure 6b).