Demographic history
Different demographic histories may lead to divergent differentiation and diversity statistics. We examined whether differences in the magnitude of drift (e.g., due to smaller population sizes) could explain differentiation across species. Demographic histories as estimated in MSMC2 largely varied by species, and in some cases populations, but was largely consistent within populations of each species (Fig. 2D). Contemporary estimated effective population sizes varied between ~50,000 to 600,000. The Abyssinian Catbird generally had a low effective population size throughout the last 200,000 years. In contrast, the Abyssinian Thrush has maintained effective populations sizes > 400,000 throughout the last 200,000 years. The Rüppell’s Robin-chat is the only species sampled here with large-scale fluctuations in estimated population sizes, with large increases in population sizes from ~50 to 80 kya. The Ethiopian White-eye exhibited slight changes in population size over the past 200,000 years, with estimated NE varying between 200,000 and 400,000. Lastly, the populations of the Brown-rumped Seedeater and the Abyssinian Slaty Flycatcher exhibited distinct population histories on either side of the GRV. Generally, within individual bootstrap replicates showed slight variation in population sizes through time but generally corroborated the full dataset results (Fig. S4). Overall, there seem to be no general patterns of demographic history through time across species, with most trends appearing to be species-specific.