Recovery directions for monoecious and endangered 'Bertya ingramii' using autecology and comparisons with common 'B. rosmarinifolia' (Euphorbiaceae)

Abstract

There is much interest in the utility of incorporating a common congener in studies of rare plants, because differences between species may be informative for conservation management. We propose here that it is the similarities between such species and even the parameters in which the rare species is comparatively more successful that can provide much useful information and opportunities. This is a benefit not often recognised within these species' comparisons. 'Bertya ingramii' (Euphorbiaceae) is a threatened shrub known only from two small populations (<70 plants in each) in northern New South Wales, Australia. Both populations are in decline with grazed and senescing individuals and very few seedlings. In contrast, 'Bertya rosmarinifolia' is widespread and was found to produce five-fold more seedlings than 'B. ingramii'. A comparative study of these species involving pre- and post-seed release factors (bud to fruit ratios, flowering synchrony, breeding system, seed-set, seed viability and seed removal rates) was undertaken to determine whether there are key factors that reduce the pre- and post-dispersal reproductive potential in 'B. ingramii'. Both species are monoecious, self-compatible and flower from August to November. In both species female flowers appear first and last, with ca. 8 weeks of intermittent synchrony between female and male flowers. In 1996, 'B. rosmarinifolia' produced more than 100% more fruit than 'B. ingramii', which in part is due to bud production which is two-fold higher in B. rosmarinifolia. Seeds in both species exhibited ca. 97% viability. Germination treatments (80, 100°C , scarified and control) revealed that for both species manual scarification produced a higher germination rate than heat or controls. An additional treatment of GA3 improved germination rates of 'B. ingramii' seeds over most non-GA3 treatments, indicating that seeds of 'B. ingramii' contain a conditional dormancy mechanism. Almost 100% of 'B. ingramii' seeds were removed from experimental trays by ants and more 'B. ingramii' seeds were removed than 'B. rosmarinifolia'. To break the extinction vortex in which 'B. ingramii' is involved, we propose human-assisted seed dispersal to safe sites, the augmenting of populations with ex situ germinated seedlings and the exclusion of herbivores from 'B. ingramii' populations. The incorporation of the common congener 'B. rosmarinifolia' was useful because it revealed that it too experienced bud loss to moths and seed removal by ants. Threat abatement for 'B. ingramii', particularly of moth damage, could be trialled on common 'B. rosmarinifolia'.