Browsing by Subject "Nectar Robbing"

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    Crypsis in non-flying mammal pollinated Proteaceae: novel adaptations and evidence of nectarivorous bird avoidance
    (2019) Connolly, Alexandra; Midgley, Jeremy
    A defining feature of the non-flying mammal pollinated (NMP) syndrome is inflorescence crypsis whereby flowers are close to the ground and somewhat hidden within the canopy. A number of species in the Cape Proteaceae are NMP, two of which were chosen as focal species for this study: Protea amplexicaulis and Protea humiflora. This study investigated the two previously suggested hypotheses for crypsis: hidden flowers are more difficult for nectarivorous birds to access, or hidden flowers provide greater cover for small mammal pollinators from aerial predators. Using remote triggered cameras, P. amplexicaulis and P. humiflora inflorescences were observed over the 2017 flowering period, noting visitation by birds and small mammals and assessing the legitimacy of birds as pollinators. In the literature, bird visitation to exposed inflorescences is suggested to be rare, but this study showed that it is considerable. Observations of camera footage suggest that birds are in fact illegitimate pollinators and thus nectar rob. Bird visitation to exposed inflorescences was more than tenfold that of hidden inflorescences, suggesting that crypsis is likely a strategy to avoid nectar robbing by birds. Both P. amplexicaulis and P. humiflora have been observed to retain dead leaves, which may contribute to their cryptic nature. Alternative hypotheses for dead leaf retention in Proteaceae – that it may increase flammability or result in a below canopy spike in nutrients post fire (selfish fertilization) – were assessed and rejected. Sampling of eight local Protea species showed that dead leaf retention is not a consequence of prolonged live leaf retention, with P. amplexicaulis retaining dead leaves for up to 6 years. The removal of dead leaves in 30 P. amplexicaulis individuals resulted in a significant decrease in the number of inflorescences hidden from aerial view, thus suggesting that dead leaf retention may be a strategy to enhance crypsis and thus forms part of the NMP syndrome. This research expands on the knowledge of the NMP syndrome; providing evidence in support of an anti- nectar robbing crypsis function, discovering a novel crypsis adaptation regarding dead leaf retention, and casting doubt on the Restricted Distributions hypothesis for the evolution of the syndrome.
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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.