Perturbation drives changing metapopulation dynamics in a top marine predator

Metapopulation theory assumes a balance between local decays/extinctions
and local growth/new colonisations. Here we investigate whether recent
population declines across part of the UK harbour seal range represent
normal metapopulation dynamics or are indicative of perturbations
potentially threatening the metapopulation viability, using 20 years of
population trends, location tracking data ( n = 380), and UK-wide,
multi-generational population genetic data ( n = 269). First, we use
microsatellite data to show that two genetic groups previously identified
are distinct metapopulations: northern and southern. Then, we characterize
the northern metapopulation dynamics in two different periods, before and
after the start of regional declines (pre-/peri-perturbation). We identify
source–sink dynamics across the northern metapopulation, with two putative
source populations apparently supporting three likely sink populations,
and a recent metapopulation-wide disruption of migration coincident with
the perturbation. The northern metapopulation appears to be in decay,
highlighting that changes in local populations can lead to radical
alterations in the overall metapopulation's persistence and dynamics.