Congruent biogeographical disjunctions at a continent-wide scale: Quantifying and clarifying the role of biogeographic barriers in the Australian tropics.

Robert D Edwards,Lyn G Cook,Dianne H Cook,Michael D Crisp,William Oki Wong

doi:10.1371/journal.pone.0174812

Robert D Edwards, Lyn G Cook + Show 3 more

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https://doi.org/10.1371/journal.pone.0174812

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Abstract

AimTo test whether novel and previously hypothesized biogeogaphic barriers in the Australian Tropics represent significant disjunction points or hard barriers, or both, to the distribution of plants.LocationAustralian tropics: Australian Monsoon Tropics and Australian Wet Tropics.MethodsThe presence or absence of 6,861 plant species was scored across 13 putative biogeographic barriers in the Australian Tropics, including two that have not previously been recognised. Randomizations of these data were used to test whether more species showed disjunctions (gaps in distribution) or likely barriers (range limits) at these points than expected by chance.ResultsTwo novel disjunctions in the Australian Tropics flora are identified in addition to eleven putative barriers previously recognized for animals. Of these, eleven disjunction points (all within the Australian Monsoon Tropics) were found to correspond to range-ending barriers to a significant number of species, while neither of the two disjunctions found within the Australian Wet Tropics limited a significant number of species’ ranges.Main conclusionsBiogeographic barriers present significant distributional limits to native plant species in the Australian Monsoon Tropics but not in the Australian Wet Tropics.

Highlights

Climatic and geographic barriers can play a major role in the diversification of organisms across landscapes by limiting species’ distributions, dispersal and gene flow
Two novel disjunctions in the Australian Tropics flora are identified in addition to eleven putative barriers previously recognized for animals
Not typically considered as part of the Australian Monsoon Tropics, we include the Pilbara (Western Australia) and coastal central Queensland because these areas experience monsoon-like rainfall patterns, Congruent biogeographic disjunctions in the Australian tropical flora even if rarely (Fig 2, modified from [17]), and because many plant species occurring in the traditionally recognised Australian Monsoon Tropics occur in these regions

Summary

Introduction

Climatic and geographic barriers can play a major role in the diversification of organisms across landscapes by limiting species’ distributions, dispersal and gene flow. Identifying such barriers has the potential to contribute to explanations of the geographic limits of species and, the genesis of species when isolation is sustained for prolonged periods of time. In Australia, up to 22 major zones of coincident turnover or common disjunction in species’ distributions have been identified as putative barriers to dispersal, primarily in vertebrates (e.g., [4,5,6]) and, while the timing and underlying causes have been robustly inferred for some (e.g., the uplift of the Nullarbor Plain dividing the temperate regions of southeast and southwest Australia [7], and the periodic connection and separation of Tasmania from the mainland [8,9]), most remain poorly defined and largely untested. Defining a stable framework that uses consistent locations, names, and definitions for putative biogeographic barriers is essential for constructing and testing hypotheses about the causes of these phenomena, as well as their role in speciation and community assembly [14]

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