In the 2012 President's Budget Request, the National Biological Information Infrastructure (NBII) is terminated. As a result, all resources, databases, tools, and applications within this web site will be removed on January 15, 2012. For more information, please refer to the NBII Program Termination page.
Not all animals that visit flowers are pollinators. Some of them may collect nectar or pollen, but because of a morphological mismatch with the flower, don't encounter the reproductive parts of the flower. Such visitors are sometimes referred to as nectar or pollen thieves, as they remove the resources that make the flowers attractive to pollinators. It may take careful observation or experimental studies to confirm whether a flower visitor is also a pollinator.
Another category of visitors that can be detrimental for plants is nectar or pollen robbers. These visitors make holes in the flowers in order to obtain floral resources. Carpenter bees (Xylocopa sp.) and some bumble bees (e.g., Bombus occidentalis) will forage as nectar robbers, and some hummingbirds or other flower-visiting birds (e.g. slaty flower piercer (Diglossa plumbea)) will also rob nectar. This behavior allows the robbers to extract nectar that they might otherwise not be able to reach (e.g., because they have a short tongue and the flower has a long corolla or flower tube). Once the holes have been made in flowers, some other insects (secondary nectar robbers) will learn to locate and use the holes too.
References: Inouye, D. W. 1980. The terminology of floral larceny. Ecology 61:1251-1253.; Inouye, D. W. 1983. The ecology of nectar robbing. Pages 153-173 in T. S. Elias and B. L. Bentley, editors. The Biology of Nectaries. Columbia University Press, New York; Maloof, J. E. and D. W. Inouye. 2000. Are nectar robbers cheaters or mutualists? Ecology 81:2651-2661.
What is a Pollinator?
A tachinid fly (Family: Tachinidae) on catnip. Photo copyright Beatriz Moisset.
A pollinator initiates fertilization of a plant by moving pollen from the male anthers of a flower to the female stigma of a flower. As pollinators get their food from the flower of the plant, they brush up against the male anthers which are covered in pollen. The pollen sticks to the pollinator, and as feeding continues from flower to flower, the pollinator rubs pollen onto the female stigma. Once fertilized, a plant will produce fruit and/or seeds that will lead to plant reproduction.
Many plants have evolved special characteristics to attract certain pollinators. Hummingbirds, for example, are attracted to brilliantly colored red to orange-red flowers that are in bloom during daylight hours.
How Does That Flower Work?
This figure of a mature flower identifies individual flower parts. Figure by Mariana Ruiz, available on Wikipedia.
Pollination is defined as the transfer of pollen, containing the male gametes, from the anther of a flower to the stigma, the female part of the flower. But just what are an anther and a stigma? Use the diagram above and the definitions below to help unlock the secrets to how pollination occurs.
The flower is the reproductive part of a plant that contains the male pollen and/or the female ovule. It consists of the calyx on the outside, the corolla lying inside the calyx, the stamens enclosed by the corolla, and the pistil in the center of the flower. The outermost whorl of a flower, called the calyx, is made up of small green leaf-like structures at the base of the flower called sepals. The calyx encloses and protects the inner whorls. Inside the calyx is the corolla, the whorl made of petals that protects the stamen and pistil. Petals serve to attract pollinators, as they are often brightly colored and sometimes scented and nectar producing. Collectively, the calyx and the corolla are called the perianth. The male reproductive part of the plant is the stamen. The stamen produces pollen grains and is made up of the filament and anther. The anther is the pollen bearing portion of the stamen and the filament bears and supports the anther. The innermost whorl is the pistil, the female reproductive part of the plant. It consists of the ovary, style, and stigma. The ovary contains the ovules and matures to become a fruit. The style bears the stigma, the receptive surface for pollen grains. Ovules contain an egg cell and, after fertilization, develop into a seed.
Additional flower parts are the pedicel, the flower stalk; the nectary, a gland-like organ that secretes nectar; the floral axis, the flower stem containing reproductive organs; articulation, the space on a stem between two nodes; and microsporangium, the structure producing microspores.
The NBII Program is administered by the Biological Informatics Program of the U.S. Geological Survey
