Pollination ecology of Tetratheca species from isolated, arid habitats (Banded Iron Formations) in Western Australia

Abstract

Pollination and reproductive ecology of arid zone species in Australia are neglected topics. This is particularly true of rare species, some of which are threatened by mining operations. The bee community at Windarling Range in southern Western Australia and the pollination ecology of four rare Tetratheca taxa with distributions restricted to Banded Iron Formation inselbergs in the arid south-west were examined in winter and spring to understand if pollination rate was affecting the reproductive ecology of the plants. The bee fauna on the Windarling Range was sampled using coloured pan traps at three landscape positions of ridge (where Tetratheca paynterae subsp. paynterae occurs), slope and flats and the insect visitors to T. paynterae subsp. paynterae were quantified by direct observation. The bee fauna varied over the two years with average richness higher in 2010 than 2011 and was higher on the ridge compared with the slope and flats below the inselberg. The Tetratheca species are buzz pollinated and T. paynterae subsp. paynterae is only visited by a subsection of the bee fauna, mainly Lasioglossum species, which were shown to be relatively faithful to the species in terms of the pollen they carried. Flowering mainly occurs after the winter wet season, but may occur at other times when there has been substantial rain. This may not coincide with bee activity. In the winter flowers may be poorly serviced if maximum daytime temperatures are below 20°C. However, in spring when temperatures are higher the majority of flowers were pollinated and there was no significant difference in proportion of pollinated flowers between the four taxa examined. As T. paynterae is outcrossing the propensity for bees to attend few flowers on a visit to each plant, often on the outer part of the plant canopy, will likely ensure a high success rate for seed formation. High seed set in such an arid environment with few suitable sites for seedling establishment is essential so some propagules can find safe sites for establishment to maintain population numbers.