Assortative Pollination by Red Wattlebirds in a Hybrid Population of Anigozanthos Labill. (Haemodoraceae)

Abstract

The specificity and spatial pattern of foraging movements of red wattlebirds (Anthochaera carunculata) were studied in a hybrid population of Anigozanthos manglesii D. Don and A. humilis Lindl in the shire cemetery at Gingin, W.A. Differences in phenology, nectar production, stem height and floral dimensions between F₁ hybrids and the two parental Anigozanthos species were also documented to assess their influence on foraging behaviour and interspecific pollen flow.

The red wattlebirds showed a 97 % fidelity for A. humilis at its seasonal peak in August 1976 and, a month later, an equally strong fidelity (97 %) for A. manglesii at its seasonal peak. Interspecific foraging movements constituted only 1.2% of the total of 925 observed during these two study periods. The spatial distribution of flowering individuals and plant stature appeared to be principal factors determining assortative pollination, presumably because of their influence on the energetics of foraging. It is suggested that the observed nearest-neighbour foraging pattern results in spatial restrictions on pollen flow and may be responsible for the confinement of hybrids to ecotonal zones where the parental species grow intermixed. Gene exchange between species is also restricted by differences in pollen deposition/retrieval sites arising from the divergent floral structures of A. hurnilis and A. rnanglesii.

It is proposed that honeyeaters have generated strong selective pressures influencing the stature, floral structure and phenology of these kangaroo paws.