Decline of a biome: evolution, contraction, fragmentation, extinction and invasion of the Australian mesic zone biota

Abstract

Aim The mesic biome, encompassing both rain forest and open sclerophyllous forests, is central to understanding the evolution of Australia's terrestrial biota and has long been considered the ancestral biome of the continent. Our aims are to review and refine key hypotheses derived from palaeoclimatic data and the fossil record that are critical to understanding the evolution of the Australian mesic biota. We examine predictions arising from these hypotheses using available molecular phylogenetic and phylogeographical data. In doing so, we increase understanding of the mesic biota and highlight data deficiencies and fruitful areas for future research.Location The mesic biome of Australia, along the eastern coast of Australia, and in the south-east and south-west, including its rain forest and sclerophyllous, often eucalypt-dominated, habitats.Methods We derived five hypotheses based on palaeoclimatic and fossil data regarding the evolution of the Australian mesic biota, particularly as it relates to the mesic biome. We evaluated predictions formulated from these hypotheses using suitable molecular phylogenies of terrestrial plants and animals and freshwater invertebrates.Results There was support for the ancestral position of mesic habitat in most clades, with support for rain forest habitat ancestry in some groups, while evidence of ancestry in mesic sclerophyllous habitats was also demonstrated for some plants and herpetofauna. Contraction of mesic habitats has led to extinction of numerous lineages in many clades and this is particularly evident in the rain forest component. Species richness was generally higher in sclerophyllous clades than in rain forest clades, probably due to higher rates of net speciation in the former and extinction in the latter. Although extinction has been prominent in rain forest communities, tropical rain forests appear to have experienced extensive immigration from northern neighbours. Pleistocene climatic oscillations have left genetic signatures at multiple levels of divergence and with complex geographical structuring, even in areas with low topographical relief and few obvious geographical barriers.Main conclusions Our review confirms long-held views of the ancestral position of the Australian mesic biome but also reveals new insights into the complexity of the processes of contraction, fragmentation, extinction and invasion during the evolution of this biome.

Pleistocene divergence across a mountain range and the influence of selection on mitogenome evolution in threatened Australian freshwater cod species

“…Movement across the GDR by Maccullochella was most likely facilitated by extreme flooding in low elevation regions of the GDR (Nock et al, 2010;Unmack, 2013). Drainage isolation as a result of increasingly dry conditions through the Pleistocene and/or increased sea levels during interglacial periods may have led to divergence between the Mary River and eastern freshwater cod east of the GDR (Byrne et al, 2011;Faulks et al, 2015).…”

“…The GDR has a strong influence on the eastern Australian climate, with topographic relief leading to a typically arid/semi-arid climate inland and more mesic conditions (mean annual precipitation: evaporation ratio of 40.4) along the coast (Byrne et al, 2011). Despite the GDR acting as a strong barrier to fish movement, many species, and species with recent shared ancestries, are found on both sides of the GDR (Unmack, 2001;Faulks et al, 2015).…”

Multiple evolutionary origins of Australian soil-burrowing cockroaches driven by climate change in the Neogene

“…Soil burrowing then evolved between three and nine times independently (figure 3). Soil burrowing is likely to have been driven by aridification events in Australia, which caused the replacement of rainforest and wet sclerophyll habitats with dry sclerophyll and scrubland [15]. The transition of mesic to xeric habitats would have led to strong selection on wood-feeding taxa to adapt to these novel environments, as the availability of moist rotting wood diminished.…”

“…These periods of aridification affected large geographical areas, including much of the eastern seaboard of Australia, from northern Queensland down to southern New South Wales and Victoria, covering a distance of approximately 3000 km [15]. The aridification of mesic habitats in eastern Australia is likely to have had strong effects on the taxa distributed in these areas, providing conditions that were conducive to the parallel evolution of traits among related species.…”

“…The last approximately 20 Myr have seen significant climatic change in Australia, with four key periods of aridity occurring over this time frame, and relatively warm and wet conditions present in the intervening periods (reviewed by Byrne et al [15]). The mesic forests that dominated the continent during the Palaeogene (66-23 Ma) began to be replaced by sclerophyllous forests from about 25 Ma.…”