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).