Abstract
ObjectivesIdentify patterns of change in species distributions, diversity, concentrations of evolutionary history, and assembly of Australian rainforests.MethodsWe used the distribution records of all known rainforest woody species in Australia across their full continental extent. These were analysed using measures of species richness, phylogenetic diversity (PD), phylogenetic endemism (PE) and phylogenetic structure (net relatedness index; NRI). Phylogenetic structure was assessed using both continental and regional species pools. To test the influence of growth-form, freestanding and climbing plants were analysed independently, and in combination.ResultsSpecies richness decreased along two generally orthogonal continental axes, corresponding with wet to seasonally dry and tropical to temperate habitats. The PE analyses identified four main areas of substantially restricted phylogenetic diversity, including parts of Cape York, Wet Tropics, Border Ranges, and Tasmania. The continental pool NRI results showed evenness (species less related than expected by chance) in groups of grid cells in coastally aligned areas of species rich tropical and sub-tropical rainforest, and in low diversity moist forest areas in the south-east of the Great Dividing Range and in Tasmania. Monsoon and drier vine forests, and moist forests inland from upland refugia showed phylogenetic clustering, reflecting lower diversity and more relatedness. Signals for evenness in Tasmania and clustering in northern monsoon forests weakened in analyses using regional species pools. For climbing plants, values for NRI by grid cell showed strong spatial structuring, with high diversity and PE concentrated in moist tropical and subtropical regions.Conclusions/SignificanceConcentrations of rainforest evolutionary history (phylo-diversity) were patchily distributed within a continuum of species distributions. Contrasting with previous concepts of rainforest community distribution, our findings of continuous distributions and continental connectivity have significant implications for interpreting rainforest evolutionary history and current day ecological processes, and for managing rainforest diversity in changing circumstances.
Highlights
Descriptions of the origins and survival of rainforest on the driest habitable continent on earth have, like the rainforest, shifted through time
Diversity measures We identified continental scale patterns of species distributions and richness for the woody component of the rainforest flora by representing species richness as raw data derived from species presences in the 10610 km grid cells (Fig. 1; and see Fig. 2)
To test the efficacy of our allocation of areas to regions and show the relations between regions we used non-metric multidimensional scaling ordination and the Sorensen distance measure (Primer v6) [50]. Outputs from these analyses showed that the merging and expansion of several regions with strong floristic affinities and similar biogeographic history (e.g. Northern Territory and Western Australia; Eungella-Proserpine and Central Queensland; Northern New South Wales and Southeast Queensland) was well founded (Fig. S1 in Appendix S1)
Summary
Descriptions of the origins and survival of rainforest on the driest habitable continent on earth have, like the rainforest, shifted through time. The massive contraction that followed occurred as a consequence of palaeogeographic and palaeoclimatic factors [5] that increased aridity and reduced the extent of the ancestral rainforest. 30 Ma increasing aridity [6] interacted with topographic and edaphic gradients [7,8] and the increasing incidence of fire to shape the area of available habitat for broad-leafed mesic vegetation [9]. The lack of major topographic relief reduced the potential buffering effect of altitude (and moist sub-montane habitats) [10] on the impact of aridity and the distribution of rainforest over much of the continent. The result was a rainforest distribution constrained mostly to the eastern side of the Great Dividing Range in eastern Australia, and a reduction in rainforest species and lineages [9,11,12]
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