4.5 Genetic diversity trends in protected areas
Several studies have reported similar levels of genetic diversity in populations located within and outside protected areas (PAs - Caló et al., 2016; Hedenäs, 2018; Novello et al., 2018; Wennerström et al., 2017; Zechini et al., 2018), but none of those studies consider the temporal aspect. Araguas et al. (2017) examined genetic diversity and introgression in brown trout populations within PAs in north-western Spain, with samples taken at more than two points in time. They observed diversity fluctuations within localities over time (albeit without statistical testing), but no general trend among localities. We have also observed significant fluctuations in genetic diversity within some of the subpopulations and/or metapopulations over time. In seven of the eight separate water systems where more than one population was identified we find decrease in genetic diversity in some subpopulations, and increase in others. Clearly, we would need to continue monitoring these systems in coming decades to see if such fluctuations of genetic diversity within and between populations are random within systems, and if they vary among populations over time.
We observe a general trend of small local N e, but with higher metapopulation N e, and migration rates between subpopulations are crudely estimated as ~0.5-2.5 individuals per generation (assuming an island model of migration). These findings suggest that the metapopulation structure buffers the systems against loss of genetic diversity and that protected areas need to be large enough to support a large meta-N e (cf. Jorde & Ryman, 1996; Gompert et al., 2021).