Abstract
We present the first extensive and integrative analysis of niche evolution based on climatic variables and a dated molecular phylogeny of a heterogeneous avian group of Southeast Asian scimitar babblers of the genus Pomatorhinus. The four main clades of scimitar babblers have species that co-occur in similar areas across southern Asia but some have diverged at different timeframes, with the most recently evolved clade harboring the highest number of species. Ecological niche models and analysis of contributing variables within a phylogenetic framework indicate instances of convergent evolution of members of different clades onto similar ecological parameter space, as well as divergent evolution of members from within clades. Pomatorhinus species from different clades occupying Himalayan foothills show convergence towards similar climatic tolerances, whereas within a clade, allopatric sister-species occurring in the Himalayas have diverged to occupy different climatic parameter spaces. Comparisons of climatic tolerances of Himalayan foothills taxa with species distributed further south in Assam/Burma and Burma/Thailand indicate convergence towards similar parameter spaces in several climatic variables. Niche overlap was observed to be lower among species of the youngest clade (ruficollis) and higher among species of older clades (ferruginosus). Analysis of accumulation of ecological disparity through time indicates rapid divergence within recent time frames. As a result, Himalayan taxa originating at different temporal scales within the four main scimitar babbler clades have differentiated ecologically only in recently diverged taxa. Our study suggests that the repeated orogenic and climatic fluctuations of the Pliocene and Pleistocene within mainland Southeast Asia served as an important ecological speciation driver within scimitar babblers, by providing opportunities for rapid geographic expansion and filling of novel environmental niches.
Highlights
Biogeography is at the interface between historical and ecological explanations for species distributions
One of the fundamental questions in biogeography is, how do species accumulate in different regions? Historical interpretations examine speciation patterns driven by processes such as vicariance and dispersal, while ecological explanations include environmental tolerance and niche partitioning
Highest species diversity was observed in the Himalayan foothills region of NE India, where up to 14 species in all four clades are predicted to occur in sympatry (Figure 1)
Summary
Biogeography is at the interface between historical and ecological explanations for species distributions. Historical interpretations examine speciation patterns driven by processes such as vicariance and dispersal, while ecological explanations include environmental tolerance and niche partitioning. We aim to address this critical question by integrating both historical and ecological inferences to examine the evolution of environmental niche occupancy using speciation patterns across different clades. Development of environmental niche modeling tools has led to numerous studies examining various aspects of species distributions including ecological determinants and historical limits of species distributions [1,2,3,4,5]. We used phyloclimatic analysis in a comparative context to determine ecological niche evolution across four separate but related clades of songbirds endemic to tropical Asia. Our main objectives were to examine how species in different clades come to occupy the same areas and evolve similar habitat requirements and contrast the ecologies of species colonizing novel areas
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