Bird and Mammal pollen vectors in Banksia communities at Cheyne Beach, Western Australia

Abstract

A study of several autumn-flowering plants at Cheyne Beach was undertaken to compare pollen loads of their bird and mammal vectors and to investigate hypotheses concerning adaptations for bird and mammal pollination in Banksia. New Holland honeyeaters, white-cheeked honeyeaters, western spinebills and honey possums were all found to carry pollen of species of Banksia, Adenanthos, Lambertia (Proteaceae), Beaufortia and Calothamnus (Myrtaceae), whereas southern bush rats and house mice carried virtually none. Honeyeaters carried significantly larger pollen loads of the Proteaceae species than did honey possums. The honey possums carried the largest loads of Myrtaceae pollen. The loads on honey possums and southern bush rats may have been underestimated because these mammals were live-trapped and may have preened themselves prior to sampling for pollen. It was found that the two dominant banksias had divergent floral characteristics, some of which previous authors had suggested were adaptations to either bird or mammal pollination (e.g. straight styles in B. baxteri as against hooked styles in B. occidentalis). However, birds and mammals appeared to feed without preference on, and carry the pollen of, both species. The net effect of the divergent characteristics of the two banksias was that B. occidentalis transferred more pollen to vertebrate vectors and set more seed per inflorescence than did B. baxteri. Further work is needed to clarify the functional roles and adaptive significance of floral characteristics in these and other banksias.