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Web Ecology An open-access peer-reviewed journal
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Volume 18, issue 1 | Copyright
Web Ecol., 18, 47-54, 2018
https://doi.org/10.5194/we-18-47-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Standard article 28 Mar 2018

Standard article | 28 Mar 2018

Why so many flowers? A preliminary assessment of mixed pollination strategy enhancing sexual reproduction of the invasive Acacia longifolia in Portugal

Manuela Giovanetti, Margarida Ramos, and Cristina Máguas Manuela Giovanetti et al.
  • Center for Ecology, Evolution and Environmental Changes (cE3c), Faculdade de Ciências da Universidade de Lisboa, Lisbon, 1749-016, Portugal

Abstract. Acacia longifolia, a native legume from Australia, has been introduced in many European countries and elsewhere, thus becoming one of the most important global invasive species. In Europe, its flowering occurs in a period unsuitable for insect activity: nonetheless it is considered entomophilous. Floral traits of this species are puzzling: brightly coloured and scented as liked by insects, but with abundant staminate small-sized flowers and relatively small pollen grains, as it is common in anemophilous species. Invasion processes are especially favoured when reshaping local ecological networks, thus the interest in understanding pollination syndromes associated with invasive plant species that may facilitate invasiveness. Moreover, a striking difference exists between its massive flowering and relatively poor seed set. We introduced a novel approach: first, we consider the possibility that a part of the pollination success is carried on by wind and, second, we weighted the ethological perspective of the main pollinator. During the flowering season of A. longifolia (February–April 2016), we carried on exclusion experiments to detect the relative contribution of insects and wind. While the exclusion experiments corroborated the need for pollen vectors, we actually recorded a low abundance of insects. The honeybee, known pollinator of acacias, was relatively rare and not always productive in terms of successful visits. While wind contributed to seed set, focal observations confirmed that honeybees transfer pollen when visiting both the inflorescences to collect pollen and the extrafloral nectaries to collect nectar. The mixed pollination strategy of A. longifolia may then be the basis of its success in invading Portugal's windy coasts.

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If during a sunny day you spot the thousands of bright yellow flowering acacias on the coast of Portugal, then ask yourself who is spreading all of that pollen around! Even if the most common answer would be bees, when the acacia flowers it is still quite cold for them. This study highlights the so far neglected role of wind in acacia seed setting, arguing the influence this may have on acacia invasiveness and theories of pollination strategy evolution.
If during a sunny day you spot the thousands of bright yellow flowering acacias on the coast of...
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