Conservation biology of two endemic Beyeria species (Euphorbiaceae) from southern Western Australia

Abstract

Beyeria cockertonii Halford & R.J.F.Hend. and Beyeria villosa Halford & R.J.F.Hend. (Euphorbiaceae) are two short-range endemic monoecious congeners from southern Western Australia. We sought to determine whether life-history characteristics were responsible for their limited distribution and to identify aspects of their ecology that might render them vulnerable to current threatening processes. We investigated reproductive phenology in relation to climate, pollinator activity and synchronicity of male and female flowering. In addition seed dispersal, regeneration, demography and seed viability were examined and ex situ germination experiments conducted to determine seed-dormancy mechanisms. Flowering in the conservation-listed B. cockertonii was significantly correlated with temperature, whereas fruit set was correlated with pollinator abundance and movement; male and female flowering showed limited synchrony. The presence of soil-stored seeds lacking a caruncle at sites absent of adult plants of either species suggests that seed may be ant-dispersed (myrmecochory). Fresh seeds of B. cockertonii were significantly more viable than those of its more common congener, B. villosa (72 vs 0.5%, P < 0.001). Fresh B. cockertonii seeds would not germinate with an intact caruncle; caruncle removal elicited germination of 64% and 60% (10°C and 15°C, respectively). Aqueous smoke further stimulated germination to 72% and 83% germination (10°C and 15°C, respectively), providing a link between fire and germination. Beyeria villosa was affected by high levels of pre-dispersal predation (up to 70%) and seed abortion (88%) and appeared to have lower reproductive fitness than B. cockertonii. Life-history strategies did not explain the greater abundance and wider distribution of B. villosa than those of the conservation-listed B cockertonii, nor was the greater rarity of B. cockertonii fully explained by habitat specificity, with both species being restricted to ultra-mafic volcanic rock associated with Achaean greenstone. However, an apparent dependence of B. cockertonii on a specific insect pollinator from the family Miridae may render this species vulnerable to threatening processes.