Data from: Evolutionary dynamics of a rapidly receding southern range boundary in the threatened California Red-Legged Frog (Rana draytonii)

Populations forming the edge of a species range are often imperiled by
isolation and low genetic diversity, with proximity to human population
centers being a major determinant of edge stability in modern landscapes.
Since the 1960s, the California red-legged frog (Rana draytonii) has
undergone extensive declines in heavily urbanized southern California,
where the range edge has rapidly contracted northward while shifting its
cardinal orientation to an east-west trending axis. We studied the genetic
structure and diversity of these frontline populations, tested for
signatures of contemporary disturbance, specifically fire, and attempted
to disentangle these signals from demographic events extending deeper into
the past. Consistent with the genetic expectations of the
‘abundant-center’ model, we found that diversity, admixture, and
opportunity for random mating increases in populations sampled
successively further away from the range boundary. Demographic simulations
indicate that bottlenecks in peripheral isolates are associated with
processes extending tens to a few hundred generations in the past, despite
the demographic collapse of some due to recent fire-flood events. While
the effects of recent disturbance have left little genetic imprint on
these populations, they likely contribute to an extinction debt that will
lead to continued range contraction unless management intervenes to stall
or reverse the process.