Conservation genetics of an island-endemic lizard: low Ne and the critical role of intermediate temperatures for genetic connectivity

Island populations are at higher risk of extinction than mainland
populations. Therefore, understanding the factors that facilitate
connectivity is particularly pressing for the conservation of island taxa.
Sceloporus occidentalis becki, the Island Fence Lizard, is an endemic
taxon restricted to the Northern Channel Islands, part of a nearshore
archipelago in Southern California, USA. Since the Last Glacial Maximum,
fence lizard habitat on the Northern Channel Islands has decreased with
rising sea levels and increasing temperatures that have reduced the
availability of woody vegetation. More recently, the introduction (and
subsequent removal) of invasive ungulates over the last 170 years
and recovery of vegetation has resulted in further dramatic habitat
modification. Given the potential for genetic bottlenecks, the history of
habitat alteration, and topographic and landscape complexity, we used
landscape and population genetic approaches to characterize patterns of
genetic diversity and structure of Island Fence Lizards on Santa Cruz
Island, the largest of the Northern Channel Islands. Our analyses revealed
shallow population structure across the island, low effective population
size (Ne = ~200), and evidence for a recent genetic bottleneck. Landscape
genetic analyses showed that connectivity is facilitated by tree canopy
cover and shrubland, as well as by intermediate temperatures, emphasizing
the importance of woody vegetation and habitats with variable thermal
regimes as the climate warms. Combined, these population and landscape
genetic analyses suggest that the Island Fence Lizard is of greater
conservation concern than currently appreciated, and increased
conservation management focus is warranted for this island endemic.