Landscape genetics Afromontane forest birds - microsatellite data

Species confined to naturally fragmented habitats may exhibit intrinsic
population complexity which may challenge interpretations of species
response to anthropogenic landscape transformation. In South Africa, where
native forests are naturally fragmented, forest‐dependent birds have
undergone range declines since 1992, most notably among insectivores.
These insectivores appear sensitive to the quality of natural matrix
habitats, and it is unknown whether transformation of the landscape matrix
has disrupted gene flow in these species. We undertook a landscape
genetics study of four forest‐dependent insectivorous songbirds across
southeast South Africa. Microsatellite data were used to conduct a priori
optimization of landscape resistance surfaces (land cover, rivers and
dams, and elevation) using cost‐distances along least‐cost pathway (LCP),
and resistance distances (IBR). We detected pronounced declines in
effective population sizes over the past two centuries for the endemic
forest specialist Cossypha dichroa and Batis
capensis, alongside recent gene flow disruption
in B. capensis, C. dichroa and Pogonocichla stellata. Landscape resistance modelling showed both native forest and dense thicket configuration facilitates gene flow in P. stellata, B. capensis and C. dichroa. Facultative dispersal of P. stellata through dense thicket likely aided resilience against historic landscape transformation, whereas combined forest‐thicket degradation adversely affected the forest generalist B. capensis. By contrast, Phylloscopus ruficapilla appears least reliant upon landscape features to maintain gene flow and was least impacted by anthropogenic landscape transformation. Collectively, gene flow in all four species is improved at lower elevations, along river valleys, and riparian corridors— where native forest and dense thicket better persist. Consistent outperformance of LCP over IBR land‐cover models for P. stellata, B. capensis and C. dichroa demonstrates the benefits of wildlife corridors for South African forest‐dependent bird conservation, to ameliorate the extinction debts from past and present anthropogenic forest exploitation.