Modelling potential Pleistocene habitat corridors between Afromontane forest regions

The unusually high floral and faunal similarity between the different regions of the Afromontane archipelago has been noted by biogeographers since the late 1800s. A possible explanation for this similarity is the spread of montane habitat into the intervening lowlands during the glacial periods of the Pleistocene, allowing biotic exchange between mountain ranges. In this study, we sought to infer the existence and most likely positions of these potential habitat corridors. We focused on sixteen Afromontane endemic tree, shrub, and bird species in the Cameroon Volcanic Line, East African Rift and Great Escarpment. Species were chosen based on distribution above 1200–1500 m in at least two of the major Afromontane regions. Ecological niche models were developed for each species in the present and projected to the mid-Holocene and the last glacial maximum (LGM). Models were thresholded to create binary maps of presence/absence and then summed across taxa to estimate potential LGM and mid-Holocene distributions. We found widespread climatic suitability for our montane taxa throughout the lowlands of Central Africa during the LGM, connecting all regions of the Afromontane archipelago except the Ethiopian Highlands and the Dahomey Gap. During the mid-Holocene, we noted more limited climatic suitability for fewer species in lowland areas. Although we set out to test predictions derived from alternatively hypothesized corridors, we instead found widespread climatic suitability connecting Afromontane regions across the entire Congo Basin for all species.