Comparative population genetic structure of the rare woodland shrub Daviesia suaveolens and its common congener D-mimosoides

Genetic (allozyme) variation and population genetic structure of the rare shrub Daviesia suaveo-lens, found in only a few large populations on the eastern escarpment of the southern tablelands of New South Wales, were compared to those of its abundant and widespread relative D. mimosoides at both spatially equivalent and rangewide scales. We hypothesized that the rare species is genetically depauperate relative to the common one. We also generated baseline data on D. suaveolens to provide management recommendations for its conservation. Both species had high variation relative to other widespread woody angiosperms. Rangewide, the rare species exhibited lower species-level genetic variation than its common relative but a similar level of variation to that found in D. mimosoides over an equivalent spatial scale. Population-level genetic variation was similar for the two species. Over its small geographic range, D. Suaveolens populations were three times as genetically differentiated as D. mimosoides over the same scale, showing a clear north-south genetic disjunction and as much interpopulation divergence as the common species exhibited range-wide. These results confirm that not all types of rarity have the same genetic implications. Conservation strategies for D. suaveolens need not be concerned about low population-level variation unless populations become significantly smaller than is currently typical. Of more importance is to maintain the high interpopulation differentiation by conserving populations from both the north and south of the species' range.