Monthly Archives: August 2013

#006 Pollination in Tropical Rainforests

Pollination is an essential service provided by invertebrates and vertebrates that supports the survival of rainforest plants. Flowers of rainforest plants are known to flower at slightly different times of the year, a phenomenon called sequential flowering. Sequential flowering has evolved by coevolution to avoid competition from pollinators, and means that at any one time a limited number of species will be in flower. This ensures that there is always nectar available for the rainforest organisms that require it and limits the intensity of competition between plants.

Rengefo et al. (2006) documented a compression mechanism in the flowers of Aphelandra runcinata. The flowers of this plant are able to shorten the length of their corolla tubes, permitting access by long and short billed birds. The classic characteristics of the ornithophilous syndrome are: yellow to red in colour; elongated corollas; narrow throat; and stamens arranged so that pollen is deposited on the visiting bird’s bill, forehead and crown. Ornithophilous flowers are also characterised by rigid corollas, to prevent damage caused by pollinators. Aphelandra runcinata however departs from the norm in this case however, as its corolla is “transversely wavy-rugose”, making it flexible. This allows species with both short and long bills to access the pollen and as a result allows the plant to be pollinated by a much wider range of species. It also perhaps decreases the risk of nectar robbing, when birds with shorter bills and limited access to the nectar of flowers with long corollas will pierce the flowers at the base, stealing nectar without performing pollination.

Bats are also important pollinators but the flowers of bat-pollinated plants display a very different syndrome to those of bird-pollinated plants. These flowers only open at night and so colour is less important, instead they tend to have a very strong scent. The energy invested by bats in foraging is large, flowers tend to only have a small amount of nectar and so bats have to visit numerous flowers per night. Tschapka and Helversen (2007) found that all flowers on an inflorescence of Werauhia gladioliflora open in the same direction, despite initial bud formation being in two rows with the flowers facing opposite directions. It is thought this may allow the bats to travel the same route to obtain nectar every night. By having a route it can follow every night, the orientation cost for the bat is reduced which may increase the pollination success of the plant.

Anoura fistulata can extend its tongue up to 8.5cm which is double the extension of any other nectar bat. This bat is able to store a large amount of nectar in its thoracic cavity.

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Rengifo, C. Cornejo, L. Akirov, I. 2006. One Size Fits All: Corolla Compression in Aphelandra runcinata (Acanthaceae), an Adaptation to Short-Billed Hummingbirds. Journal of Tropical Ecology. Vol. 22, No. 6, pp. 613-619.

Tschapka M. v Helversen, O. 2007. Phenology, nectar production and visitation behaviour of bats on the flowers of the bromeliad Werauhia gladioliflora in a Costa Rican lowland rain forest. J Trop Ecol 23:385-395.