The influence of pollinators on fruit positioning in the Australian
shrub Telopea speciosissima (Proteaceae).
Goldingay, R. L., Whelan, R. J.
Dept of Biological Sciences, Univ. of Wollongong, NSW 2522, Australia.
Oikos 1993. 68: 501-509
CAB Abstract 950312234
The waratah, T. speciosissima, produces more than 60% of fruits in the top third of its inflorescences where the flowers are the last to complete anthesis. Field studies were conducted during anthesis of a dense population of waratahs in the Barren Grounds Nature Reserve, Australia, in 1987-89, to test the following 3 hypotheses which may account for this positioning of fruits: the flowers at the bottom of inflorescences have only a male function; fruit abortion occurs more commonly at the bottom of inflorescences; and pollination is greater in the top third of an inflorescence. Hand-pollinations of flowers in the bottom third of inflorescences showed that these flowers had the same capacity to develop into fruits as the flowers in the top third. Contrary to the prediction of the second hypothesis, fruit abortion was greatest in the top third of inflorescences where most fruits were initiated, suggesting that pollination levels were also greatest there. Exclusion of pollinators from the top third of inflorescences eliminated fruit set in that region and resulted in a larger number of inflorescences failing to produce fruits. Plants were unable to compensate by maturing more fruits in the lower portions of inflorescences. Therefore the preponderance of fruits in the top third of waratah inflorescences is most likely caused by the behaviour of pollinators, probably because of a greater number of visits by pollinators to inflorescences at this stage of opening. Birds were the most abundant floral visitors and their numbers were closely related to the abundance of open inflorescences. These results are discussed in relation to the various proximate and ultimate hypotheses which attempt to account for the low fruit:flower ratios in hermaphroditic plants.