Abstract
The Afromontane mountains are a complex series of highlands that have intermittently been connected by habitat corridors during climatic cycles, resulting in a mosaic of range disjunctions and allospecies complexes in the present day. Patterns of community relatedness between geographic regions are often determined through single-species analyses or spatial analyses of diversity and nestedness at the species level. To understand patterns of Afromontane community evolution and to assess the effects of taxonomy on our understanding of biogeographic patterns, I concatenated three lists of Afromontane bird taxa divided into five taxonomic hierarchies. These lists were converted into a presence-absence matrix across 42 montane regions and analyzed using a variety of clustering techniques based on a replicable coding pipeline. I used these lists and methods to determine patterns of relatedness between montane blocks, to assess the consistency with which biogeographic regions were recovered, and to shed light on the patterns of connectivity within the Afromontane region. My results reaffirm the distinctiveness of many biogeographic regions (e.g., the Cameroon Highlands) while also clarifying regional relationships and the presence of 'transition zones' between regions. Differences between lists illustrated how our understanding of taxonomy and distribution in the Afromontane highlands can also change our understanding of Afromontane biogeography. Most notably, I found evidence for an Expanded Eastern Arc that included the Eastern Arc Mountains and highlands in Malawi, Mozambique, and Zimbabwe. This study presents a rigorous yet easily adjustable pipeline for studying regional biogeography from multiple taxonomic perspectives using both traditional and novel approaches.
Highlights
For hundreds of years, scientists have studied the ways in which montane communities are assembled and maintained (Rahbek et al 2019)
An example of both phenomena for birds is the Phasianidae genus Xenoperdix (Svendsen et al, 1994), a relative of the Southeast Asian genus Arborophila (Hodgson, 1837). This relict genus has persisted in the Eastern Arc Mountains of Tanzania, where the complex regional geography and climatic cycling has promoted the differentiation of two geographically proximate taxa that are often regarded as separate species (Dinesen et al 1994, Bowie and Fjeldså 2005)
I expanded this list by including species with endemic montane populations that are more widespread outside of the study region (e.g., Anthus similis; Jerdon 1840), species that are found in lower-lying montane regions that are more xeric (e.g., Columba oliviae in the Somalian Highlands; Clarke 1918), species that are geographically restricted around montane regions (e.g., Monticola rupestris; Vieillot 1818), and species that are elevational migrants within specific montane regions (e.g., Vanellus melanopterus; Cretzschmar 1829)
Summary
Scientists have studied the ways in which montane communities are assembled and maintained (Rahbek et al 2019). Cooper endemism appear to result from two complementary processes: (i) environmental changes that have allowed for ranges to expand and contract through time (e.g., the Turnover-Pulse Hypothesis sensu Vrba, 1993) and (ii) relatively stable climates in montane regions that allow for diversification while buffering against extinction (Prigogine 1987, Fjeldså and Bowie 2008, Fjeldså et al 2011, Couvreur et al 2020 ) An example of both phenomena for birds is the Phasianidae genus Xenoperdix (Svendsen et al, 1994), a relative of the Southeast Asian genus Arborophila (Hodgson, 1837). The consistency of overlap between Afromontane regions with respect to the distributions of species with varying levels of diversification suggest that similar colonization patterns led to modern distributions for a majority of taxa
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