Fine‐scale barriers to connectivity across a fragmented South‐East Asian landscape in six songbird species

Abstract

Habitat fragmentation is a major extinction driver. Despite dramatically increasing fragmentation across the globe, its specific impacts on population connectivity across species with differing life histories remain difficult to characterize, let alone quantify. Here, we investigate patterns of population connectivity in six songbird species from Singapore, a highly fragmented tropical rainforest island. Using massive panels of genome-wide single nucleotide polymorphisms across dozens of samples per species, we examined population genetic diversity, inbreeding, gene flow and connectivity among species along a spectrum of ecological specificities. We found a higher resilience to habitat fragmentation in edge-tolerant and forest-canopy species as compared to forest-dependent understorey insectivores. The latter exhibited levels of genetic diversity up to three times lower in Singapore than in populations from contiguous forest elsewhere. Using dense genomic and geographic sampling, we identified individual barriers such as reservoirs that effectively minimize gene flow in sensitive understorey birds, revealing that terrestrial forest species may exhibit levels of sensitivity to fragmentation far greater than previously expected. This study provides a blueprint for conservation genomics at small scales with a view to identifying preferred locations for habitat corridors, flagging candidate populations for restocking with translocated individuals and improving the design of future reserves.

Bird diversity on shelf islands does not benefit from recent land‐bridge connections

“…This short buffer distance puts the scale of overwater dispersal in Sundaic birds into perspective: although birds are thought to be one of the most vagile animal groups, this result suggests that overwater dispersal mostly occurs across relatively short distances among the resident regional birds. Many tropical species are reluctant to fly across ecological barriers such as waterbodies and in some, even just habitat fragmented by road (Cros, Ng, et al, 2020; Develey & Stouffer, 2001; Laurance et al, 2004; Moore et al, 2008; Sadanandan & Rheindt, 2015). The maintenance of diversity on islands is highly reliant on the presence of larger or stepping‐stone islands within close proximity.…”

Gene Flow in Volant Vertebrates: Species Biology, Ecology and Climate Change

“…Even volant vertebrates are not immune to habitat destruction and lack of gene flow and loss of genetic diversity is observed. Genetic differentiation, due to habitat destruction was observed in insectivores birds in the island of Singapore 15 . Due to habitat destruction, forest-dependent understorey birds are unable to move between forest patches 15 .…”

“…Genetic differentiation, due to habitat destruction was observed in insectivores birds in the island of Singapore 15 . Due to habitat destruction, forest-dependent understorey birds are unable to move between forest patches 15 . Similarly, in the Sholas of the Western Ghats, habitat loss has prevented the endemic White-bellied Shortwings from moving across recently fragmented habitats 71 .…”

“…NGS data has also helped in identifying various barriers to gene flow like physical features of the Earth (e.g rivers and oceans) as well as species attributes (e.g habitat preferences) 14 , 23 , 41 , 56 . For instance, unexpected fine-scale populations structure was revealed in forest-dependent birds within a small forested region of the island nation of Singapore when thousands of genomic markers were used 15 . Although, we have made great progress in utilizing NGS data for volant vertebrates, but our knowledge is still in its infancy especially for bats, where only a handful of studies exist.…”

Island Biogeography Revisited: Museomics Reveals Affinities of Shelf Island Birds Determined by Bathymetry and Paleo-Rivers, Not by Distance to Mainland

“…We focus on two widespread and characteristic Sundaic bird species complexes, the black-capped babbler ( Pellorneum capistratum ) and short-tailed babbler ( P. malaccense ), both sedentary rainforest denizens foraging in the understory ( Eaton et al 2016 ). Both these songbirds are known for their ubiquitous occurrence across a wide range of Sundaic lowland and hill rainforests and their general inability to cross even narrow nonforest gaps, especially open water ( Zakaria et al 2014 ; Sadanandan and Rheindt 2015 ; Cros, Ng, et al 2020 ). We characterized and compared variation in plumage patterns using a series of museum specimens to assess whether morphological differentiation is congruent with the population-genomic signal.…”