Testing tropical biogeographical regions using the palm family as a model clade

Abstract

AbstractAimSince Wallace's and Engler's 19th‐century biogeographical schemes, biogeographers have sought to classify the world into biogeographical regions according to patterns in biotic distribution. Yet, while most of the world's plant biodiversity can be found in the tropics, basic phytogeographical relationships and boundaries within this zone remain debated. We investigated whether palms, a species‐rich, well‐studied pantropical family, reflect traditional floristic schemes or support a recently published phylogenetic regionalisation that contests the traditional views on phytogeographical tropical regions.LocationTropics and subtropics.TaxonPalm family (Arecaceae).MethodsWe use a species‐level dated phylogenetic tree of palms along with a dataset of all palm species distributions to calculate pairwise phylogenetic beta diversity among palm assemblages. From these pairwise dissimilarity values, we compute the relationship between assemblages in NMDS ordination space and use hierarchical clustering to define biogeographical units for palms.ResultsWe found a Neotropical versus Palaeotropical division of palm assemblages as the major biogeographical split. Two Neotropical and four Palaeotropical clusters were identified with the following relationships: ((Southern Neotropical, Northern Neotropical), ((Indian Ocean), ((African), (Eurasian‐Australian, Melanesian‐Pacific)))).Main ConclusionsOur analysis supports many delineations suggested in traditional floristic schemes, most importantly a clear Neotropical versus Palaeotropical division and units resembling Takhtajan's African, Indo‐Malesian, New Caledonian and Polynesian Palaeotropical subkingdoms. However, as recently suggested in phylogenetic regionalisation, our results also show a clustering of Southeast Asian and Australian assemblages, substantiating the suggestion of a combined Asian‐Australian region. Biogeographical regionalisation for palms does not support the existence of trans‐continental dry tropical or subtropical phytogeographical clusters that have recently been found in dicot trees, despite known Northern Hemisphere connections for palms. Further modern regionalisations based on multiple datasets with complementary strengths are needed to establish a credible set of phytogeographical regions for the tropics.