Predominant colonization of Malesian mountains by Australian tree lineages

Abstract

Abstract Aim: Massive biota mixing due to plate‐tectonic movement has shaped the biogeography of Malesia and during the colonization process, Asian plant lineages have presumably been more successful than their Australian counterparts. We aim to gain a deeper understanding of this colonization asymmetry and its underlying mechanisms by analysing how species richness and abundance of Asian versus Australian tree lineages in three Malesian subregions change along environmental gradients. We hypothesize that differing environmental histories of Asia and Australia, and their relation to habitats in Malesia, have been important factors driving assembly patterns of the Malesian flora. Location: Malesia, particularly Sundaland, the Philippines and Wallacea. Taxon: Seed plants (trees). Methods: We compiled plot‐level data of environmental variables and tree abundances from three Malesian subregions. For each species, we inferred its geographical ancestry (Asian or Australian) based on published phylogenetic studies and the fossil record. We used proportions of Australian versus Asian species and individuals per plot to test how they are related to environmental parameters and geographical position using logistic regression models. Results: Proportionally more Australian (and fewer Asian) tree species and individuals occurred (a) at higher elevations, (b) on sites over ultramafic parent material and (c) closer to their source region Australia with a significant increase of Australian elements east of Wallace's line. The trend was stronger for individuals than for species. Main conclusions: Long‐term environmental similarities between source and sink habitats have shaped the assembly of the Malesian flora: Tree lineages from tropical Southeast Asia predominantly colonized the Malesian lowlands and rich soils, whereas trees from montane refuges in Australia were more successful in the newly emerging Malesian mountains and on poorer soils. The biogeographical patterns caused by the Malesian Floristic Interchange point to the importance of phylogenetic biome conservatism in biotic interchanges and resemble