The influence of geographic range on species persistence has long been of interest and there is a need for a better understanding of the genetic consequences for species with restricted distributions, particularly with the increasing rate of global species extinctions. However, the genetic effects of restricted range are often confounded by the impacts of population distribution. We compared chloroplast and nuclear genetic diversity and differentiation in two acacias, the restricted, patchily distributed Acacia atkinsiana and the widespread, semi-continuously distributed A. ancistrocarpa. Lower intra-population diversity and higher differentiation between populations were seen in A. atkinsiana compared to its widespread congener, A. ancistrocarpa. There was little evidence of geographical influences on population genetic structure in A. ancistrocarpa whereas A. atkinsiana exhibited nuclear genetic structure with isolation by distance, differentiation of near-coastal populations from those in the ranges, and differentiation of peripheral populations from those in the centre of the distribution. These results are consistent with expectations of the effect of geographic range and population distribution on genetic diversity, but indicate that distribution of populations rather than geographic range has influenced the observed genetic structure. The contrasting patterns observed here demonstrate that conservation approaches for species management and ecological restoration need to consider the distribution of populations in geographically restricted species.

Verticordia staminosa C.Gardner & A.C.George subsp. staminosa is an extremely rare shrub occurring as an isolated population of ~1200 plants on a granite outcrop in the semi-arid agricultural region of Western Australia, separated from its closest relative V. staminosa subsp. cylindracea by 400 km. We aimed to determine a hierarchy of causes for explaining the extremely restricted distribution of subsp. staminosa, and to determine the genetic relationships among populations within both subspecies. We measured allozyme variation in all known populations of the two subspecies. There were exceptionally high levels of genetic divergence between subsp. staminosa and subsp. cylindracea, including an apparent duplication of the gene encoding phosphoglucomutase, leading to an additional gene in subsp. cylindracea. These findings combined with UPGMA analysis indicate a very long period of historical separation, perhaps originating in the early Pleistocene. Genetic variation was partitioned mostly between rather than within populations, with very low levels of genetic variation within populations of both subspecies. For subsp. staminosa we quantified seed production for three consecutive years and demography for five consecutive years. We used transition matrix models to describe the shrub’s population dynamics and stochastic simulations to explicitly compare the effects of low rainfall and disturbance on population viability. Verticordia staminosa subsp. staminosa produces large numbers of seeds each year and has flower to fruit ratios greater than reported for related rare and common congeners. Seedling recruitment occurs in most years, with pulses in the wettest years. The mean finite population growth rate was 1.031. Elasticity analyses showed that population growth rate was more sensitive to stasis of established plants than to seedling recruitment. Population viability declined with lower rainfall and increased fire-related mortality of adult plants. Rarity in subsp. staminosa is best explained by evolutionary history and the interaction of climate change and disturbances such as fire that kill plants. Climatic fluctuations since the late Pliocene might have led to stochastic extinction episodes of populations on other granite outcrops, resulting in the currently restricted distribution. We discuss the implications of our findings for management of the species.

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.

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