Spatial distribution pattern of taxonomic and phylogenetic diversity of woody flora in Andaman and Nicobar Islands, India

Abstract

Background: The insular nature and unique geographical set up of Andaman and Nicobar Islands has led to the evolution of variety of rare and distinct flora with high endemism. Despite several efforts to document the floristic richness of the islands, there are no efforts to understand the spatial patterns in the taxonomic and phylogenetic diversity, and thence to arrive at the biogeographic origin and evolutionary history of the vegetation of this Island archipelago. Methods: We used a fine scale spatial distribution and abundance data of woody plants documented from 841 grids along with their phylogenetic data and estimated metrics of taxonomic and phylogenetic similarity to identify taxonomically and phylogenetically distinct woody plant ‘phytoregions’ within Andaman and Nicobar Islands. We then arrived at the spatial patterns of the taxonomic richness and diversity and, of phylogenetic diversity across the entire Archipelago. Results: We found that taxonomic richness and diversity of woody flora is high in Andaman and low in Nicobar Islands, whereas Nicobar Islands have a more phylogenetically diverse woody flora compared to Andaman. We identified three distinct woody plant ‘phytoregions’ within Andaman and Nicobar Islands. The three identified ‘phytoregions’ broadly match with the geographically isolated Island groups such as Andaman, Car Nicobar and Great Nicobar Islands; these ‘phytoregions’ also highlight the existence of two broadly distinct biogeographic zones of woody plants within the Islands. Conclusion: Our analysis provides new insights into the spatial patterns of diversity of woody flora in Andaman and Nicobar Islands. We show that (i) both taxonomic and evolutionary affinities identify distinct ‘phytoregions’ closely segregated across the geographic distribution of the major islands of the archipelago, and (ii) there are two distinct biogeographic zones, i.e. Andaman flora most closely allied with flora of South western Burma and Nicobar more related with the flora of Malayan peninsula and Sumatra.