Pollinators

Introduction

Pollinators are creatures that can move pollen from the pollen-producing portion of a flower to a portion of another flower where fertilization (pollination) will occur.

In the natural world, many creatures are pollinators; estimates range up to 200,000 species, most of which are insects. However, other cold- and warm-blooded creatures, including humans, are pollinators. Examples of pollinators include bees, wasps, butterflies, bats, primates, reptiles, and birds (including hummingbirds). Often they are attracted to the bright color of the plant, which has adapted to exploit the reproductive advantage gained by attracting pollinating insects and other species.

Some pollinators have also been efficiently designed for the task during their evolution. A good example is the honeybee, which can pick up pollen on specialized regions of its limbs during its foraging for nectar from plants. Upon visiting another plant the pollen can be deposited. Other creatures including humans are usually accidental pollinators, transferring pollen by brushing against plants. However, beekeepers and others who are interested in raising plants for commercial purposes or as a preservation strategy can be pollinators by choice.

Pollinators are essential for a healthy ecosystem, since only about 10% of flowering plants are able to transfer pollen without the assistance of pollinators. Although pollination can be achieved by wind, with the pollen alighting on a flower after drifting in the breeze, pollinators greatly increase the likelihood of pollination since their feeding deliberately takes them from flower to flower.

In another environmental role, pollinators that are migratory species can be an early indicator of environmental deterioration. For example, honeybee populations can decline markedly in number suddenly. One reason for this so-called colony collapse syndrome may be the infection of the population with a virus. As another example, the decline in numbers of Monarch butterflies following their winter migration in Mexico has been linked to climate change and loss of their habitat due to logging.

Historical Background and Scientific Foundations

Pollen is a powdery appearing material that is composed of grains that are termed microgametophytes. These are the sperm cells produced by the male portion of a plant called the anther. Pollinators function by transferring pollen from the anther to the carpel of another plant. The carpel contains the ovule, which is the part of the plant where the reproductive cells are located. In some varieties of plants, the target area of the carpel is known as the stigma, while in other types of plants it is called the micropyle.

The best-known pollinator is the bee. Images of a bee with a ball of adhering pollen on its rear limbs are a feature of many biology textbooks. The fuzzy texture of the limbs and body, and electrostatic charge, allow pollen to easily stick to the bee. As well, bees have specialized pollen carrying containers (“pollen basket”) on their rear limbs.

The transfer of pollen occurs when the creature lands or brushes against a flower. Often, this can be to acquire some of the flowers’ sweet nectar. When the same thing occurs on another plant, some of the pollen can be dislodged.

The deliberate human version of pollination is typically done using a brush or cotton swab to transfer the pollen. Just shaking a self-pollinating flower like the tomato can be sufficient.

Impacts and Issues

Pollinators are a vital part of the global ecosystem. Pollination is necessary for the production of seeds and fruit by about 80% of all the plants that produce a flower. This includes over 60% of the food plants in developed and underdeveloped regions of the world.

As well, pollinators are vital in maintaining the genetic diversity of plants, since their transfer of pollen is random. Genetic diversity is desirable especially for crop plants. For example, the deliberate creation of genetic uniform plant species (as is increasingly accomplished with genetically engineered crop plants) increases the risk that a disease that can infect the plant will decimate the population. With diversity, however, the population is less affected by disease, since some plants will survive and thrive.

Aside from their value to nature, pollinators can be sentinels of environmental change. For example, the decline in the Monarch butterfly population has been

WORDS TO KNOW

BIOMASS: The sum total of living and once-living matter contained within a given geographic area; or, organic matter that can be converted to fuel and is regarded as a potential energy source.

ECOLOGY: The branch of science dealing with the interrelationship of organisms and their environments.

ECOSYSTEM: The community of individuals and the physical components of the environment in a certain area.

HABITAT: The natural location of an organism or a population.

traced to its increased difficulty in overwintering in areas of Mexico. These regions have become colder in recent decades, perhaps due to the effects of global climate change. As well, the butterfly’s habitat has diminished due to logging of forests.

Because pollinators rely on the presence of flowers for their activity, climate changes that affect flowers will affect pollinators. A study that has been conducted in the Rocky Mountain region of the United States since 1973 has documented that the earlier blooming of plants in spring has occurred coincident with climate-related temperature increase. The altered blooming timing of the flowers may be disrupting pollinator activity, which, in the longer term, could threaten the survival of both the plants’ species and the pollinators.

Similar declines in plant and pollinator species have been documented in Britain and the Netherlands in a 2006 study published in the journal Science.

See Also Biodiversity; Habitat Loss

BIBLIOGRAPHY

Books

Belk, Colleen, and Virginia Borden. Biology: Science for Life with Physiology. New York: Benjamin Cummings, 2006.

Horn, Tammy. Bees in America: How the Honey Bee Shaped a Nation. Lexington: University of Kentucky, 2006.

Wasser, Nickolas, and Jeff Ollerton. Plant-Pollinator Interactions: From Specialization to Generalization. Chicago: University of Chicago Press, 2006.

Periodicals

Biesmeijer, J. C., et al. “Parallel Declines in Pollinators and Insect-Pollinated Plants in Britain and the Netherlands.” Science 313: 354–357 (2006).