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Aim Topographically complex areas are hypothesized to be mesic refugia in arid environments during periods of climatic change. We tested the hypothesis that an elevated and topographically complex range has been a historical refugium in an arid environment during Pleistocene climatic oscillations for a widespread eucalypt. Location Pilbara region, north-west Australia. Methods We evaluated genetic diversity and differentiation in chloroplast and nuclear genomes using microsatellite loci in 20 populations of Eucalyptus leucophloia from across the distribution in the Pilbara bioregion, including two ranges with differing topographical complexity and elevation. We evaluated phylogeographical structure using Permut and Network analysis, and assessed genetic structure using principle coordinate (PCoA) and Bayesian analyses. Results We found moderate levels of genetic diversity and low genetic differentiation among populations, typical of widespread eucalypts. There was no evidence of genetic structure across the sampled range. Populations in both the Hamersley and Chichester ranges showed higher levels of chloroplast haplotype and nuclear diversity than those in surrounding areas. Diversity was negatively correlated with evapotranspiration, and positively correlated with precipitation. Main conclusions Genetic signals of high diversity and low differentiation indicated population persistence throughout historical climate change in ranges, with a signal of expansion in surrounding areas. Our analysis was consistent with the hypothesis of the elevated, topographically complex Hamersley Range acting as a refugium, but revealed an unexpected result of the lower elevation, less rugged Chichester Range also being a refugium. Our results suggest refinement to expectations of environmental characteristics that facilitate persistence, where thresholds of mesic environments for refugia may be lower than expected and moisture availability may be an important contributory aspect of elevation and topographical complexity. In contrast to patterns in reptile species, lack of genetic structure associated with geological substrate and geomorphological features indicates dispersal is not impeded by these landscape features for this widespread eucalypt. [ABSTRACT FROM AUTHOR]

Species turnover and its components related to replacement and nestedness form a significant element of diversity that is historically poorly accounted for in conservation planning. To inform biodiversity conservation and contribute to a broader understanding of patterns in species turnover, we undertook a floristic survey of 160 plots along an 870 km transect across oligotrophic sandplains, extending from the mesic south coast to the arid interior of south-western Australia. A nested survey design was employed to sample distances along the transect as evenly as possible. Species turnover was correlated with geographic distance at both regional and local scales, consistent with dispersal limitation being a significant driver of species turnover. When controlled for species richness, species replacement was found to be the dominant component of species turnover and was uniformly high across the transect, uncorrelated with either climatic or edaphic factors. This high replacement rate, well documented in the mega-diverse south-west, appears to also be a consistent feature of arid zone vegetation systems despite a decrease in overall species richness. Species turnover increased rapidly with increasing extent along the transect reaching an asymptote at ca. 50 km. These findings are consistent with earlier work in sandplain and mallee vegetation in the south-west and suggests reserve based conservation strategies are unlikely to be practicable in the south-western Australia sandplains when communities are defined by species incidence rather than dominance. [ABSTRACT FROM AUTHOR]

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