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Seasonal Variation in Flowering Intensity and Pollination Limitation of Fruit Set in Four Co-Occurring Banksia Species

B. J. Copland and R. J. Whelan
Journal of Ecology
Vol. 77, No. 2 (Jun., 1989), pp. 509-523
DOI: 10.2307/2260766
Stable URL: http://www.jstor.org/stable/2260766
Page Count: 15
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Seasonal Variation in Flowering Intensity and Pollination Limitation of Fruit Set in Four Co-Occurring Banksia Species
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Abstract

(1) Patterns of flowering, levels of fruit set and pollination limitation of fruit set were examined over four years in a group of four co-occurring Banksia species (Proteaceae) in south-eastern Australia. (2) Mean numbers of inflorescences per plant varied markedly between years, but the timing of onset, peak and completion of flowering was relatively consistent among years for all species. (3) Three of the four species studied flowered in winter, and flowering times for these three overlapped substantially. (4) Fruit set in the three winter-flowering species varied both within and between years. Variation was caused by differences in the proportions of inflorescences successfully setting fruit and not by differences in numbers of fruits produced per inflorescence. (5) Fruit set in Banksia ericifolia was examined in detail. The proportion of inflorescences setting fruit was generally lower in late-season samples than earlier each year. Resource limitation probably explained this because experimental additions of outcross pollen failed to increase fruit set in late-season inflorescences in any year. (6) Pollen-supplementation did increase fruit set in B. ericifolia on one occasion: peak flowering in 1985. This was the time of highest flowering intensity during the four years of the study. Fruit set in B. spinulosa and B. paludosa was also increased by pollen supplementation in this year. These results indicate that pollination was limiting fruit set in 1985. Further, they suggest that interspecific competition among plants for pollination may be occurring and should be examined directly. (7) Approximately half of the inflorescences produced by the B. ericifolia plants studied over the four years of the study appeared during peak flowering in 1985. The greatest contribution to the seed bank, which is stored in the canopy until released by a future fire, therefore occurred at this time. (8) Limitation of fruit set by ineffective pollination, although it may occur only rarely, can thus have a disproportionately large impact on reproductive success over a relatively long inter-fire period.

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