Data from: Islands within islands: two montane paleo-endemic birds impacted by recent anthropogenic fragmentation

Gene flow between populations is affected in historic time by natural processes and more recently by anthropogenic impacts. Habitat fragmentation is known to limit gene flow and can potentially drive extinction. Effects of habitat fragmentation on species that live in habitats with natural patchiness, such as species living on mountaintops or sky islands, have rarely been examined. We predicted that populations living in naturally patchy habitats would have high historic genetic differentiation as well as high contemporary isolation, while populations in anthropogenic fragments may have low historic differentiation. We sampled 218 individuals from two sister species in the Western Ghats. We examined historic and contemporary geneflow across natural and anthropogenic patches in these sky-island restricted, endemic birds using 14 microsatellites. We detected major genetic structuring by deep valleys and describe the location of one hitherto undescribed barrier. As predicted, we found strong effects of historic genetic differentiation across natural patches, but not across anthropogenic fragments. Contrastingly, contemporary differentiation was higher relative to historic differentiation in anthropogenic fragments. Simulations revealed that high contemporary differentiation and low historic differentiation as seen in anthropogenic fragments are observable in the context of relatively recent isolation. We suggest that anthropogenic fragmentation affects population connectivity in this landscape in addition to the natural patchiness, making anthropogenic fragments akin to islands within natural islands of montane habitat. Despite these genetic effects, we suggest that these remnant anthropogenic fragments may function as corridors for movement within production landscape matrix, and urge the urgent need for their conservation