Browsing by Author "Johnson, S D"

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    Experimental evidence for bird pollination and corolla damage by ants in the short-tubed flowers of Erica halicacaba (Ericaceae)
    (Elsevier, 2012) Turner, R C; Midgley, J J; Barnard, P; Simmons, R E; Johnson, S D
    Unrelated plants pollinated by similar animals tend to show convergent evolution of floral traits. Floral syndromes have been used successfully to develop hypotheses about pollination systems but can be misleading when plants have unusual floral morphology or mechanisms of pollen transfer. A case in point is Erica halicacaba, a local endemic shrub on the Cape Peninsula of South Africa. Its short-tubed greenish-yellowish flowers with a narrow aperture have been considered to be insect pollinated. However, field observations, selective exclusion experiments and analysis of pollen loads all indicate that its primary pollinator is the Orange-breasted Sunbird (Anthobaphes violacea). These sunbirds were common visitors and netted individuals carried large numbers of E. halicacaba pollen tetrads on their culmens, rather than on their head plumage as is typical for Cape Erica species with longer tubular flowers. Plants of E. halicacaba from which vertebrates were excluded had a lower incidence of anther tripping and set significantly fewer seeds than those exposed to both birds and insect visitors. Nectar in E. halicacaba is present in small concentrated amounts and, typical of sunbird-pollinated plants, is dominated by sucrose. Flowers often had holes in their corollas and we identified ants, specifically Myrmicaria nigra, as the likely agents. This was supported by reduced rates of corolla damage on branches from which crawling insects such as ants were experimentally excluded. These findings indicate that considerable caution should be applied when attempting to predict pollinators from floral syndromes, and highlight the role that crawling insects can play in damaging flowers.
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    Insect pollination in the African cycad Encephalartos frederici-guilielmi Lehm
    (2009) Suinyuy, T N; Donaldson, J S; Johnson, S D
    Studies of the pollination ecology of the South African cycad, Encephalartos friderici-guilielmi Lehm, were carried out to determine the role played by insects and to identify the key pollinators. Surveys of insects on the male and female cones at the time of pollination indicated that three beetle species were present in sufficient numbers during pollination to be potential pollinators, i.e. an undescribed Erotylidae sp. (Cucujoidea), Metacucujus encephalarti (Cucujoidea), and Porthetes hispidus (Curculionidae). Pollen laden specimens of all three species were found on female cones with mean pollen loads ranging between 391 and 1019 pollen grains per beetle. In behavioural experiments, individuals of P. hispidus and M. encephalarti deposited fluorescent dye on the micropyles of receptive ovules. Enclosure of pollen laden specimens of P. hispidus, M. encephalarti, or Erotylidae sp. nov. on female cones resulted in seed set that was statistically similar to open controls and significantly higher than insect exclusion treatments. These data support the conclusion that E. friderici-guilielmi is insect pollinated and provide further evidence for the role of cucujoid (Erotylidae, Boganiidae) and curculionoid (Porthetes) beetles in the pollination of Encephalartos spp.