BACKGROUND INFORMATION:

Flowers and Reproduction

For a flowering plant to make its seeds and therefore reproduce, pollination must occur. Pollen must be carried from the anthers of one flower to the stigma of another. Pollen is most often carried by insects, but may also be carried by birds, bats, and even the wind. Once the pollen grains reach the stigma, the pollen germinates. One cell of the pollen grain grows into a pollen tube which reaches from the stigma, through the style and into the ovary. The other cell in the pollen grain divides into two sperm cells. One sperm fertilizes the egg, and the other joins with other cells in the flower's ovary to produce tissues that will feed and nourish the seedling until leaves form and photosynthesis can begin.

Reproductive Process of a Flowering Plant

(Click icon to see image.)

Variation and Adaptation

A variation is a trait or behavior that makes one plant or animal different from other of the same species. For example, flowers come in different colors and shapes. Some are white and some are red, some have fragrance and some don't, some are flat and wide and some are tall and narrow. Bean plants produce beans with different numbers of seeds. Some beans have only one or two seeds, and some beans have as many as nine or ten beans. Dogs come in different colors. Some are white, some are brown, and some are black. These variations can help plants and animals survive in their environment.

The color of dogs and the number of seeds in a bean pod are variations. Sometimes a variation will be an advantage because it may give the plant or animal a better chance for survival. When a variation gives a plant or animal a better chance for survival, it is called an adaptation. One good example of adaptation is the large feet of the snowshoe rabbit. These rabbits are hunted by wolves. The rabbit's large feet enable it to run faster in the snow, thereby escaping from the wolves. Occasionally, some snowshoe rabbits are born with small feet. Because they cannot run as fast on their small feet, they are more often caught by the wolves, and therefore do not reproduce as often. Therefore, not many snowshoe rabbits with small feet are born, because it is not helpful to their survival. Other examples of adaptations are listed in the chart below.

Plant or Animal Adaptation

Natural selection is the process where living things that are more well adapted to their environment are more likely to survive and reproduce, just like large-footed snowshoe rabbits are more likely to survive and reproduce than small-footed snowshoe rabbits,

Flowering Plants and Their Pollinators

Just what is it that makes bees attracted to some flowers and not others? Why does a bright red and orange flower attract butterflies? Flowering plants live thrive on every continent, in all kinds of environments--from snow-topped mountains to steamy rainforests. They come in every conceivable variety. How did this diversity--many differences--happen? And how did flowers come to grow in every habitat of the world?

According to geologic history, earth's earliest plants consisted of tiny plants floated on the water.

Pond Algae--Enlarged about 100 Times

About 400 million years ago, the first plants began to grow and develop on land. These early plants had no roots, leaves, or flowers. They reproduced by dropping spores on the ground which grew into new plants.

Early Plants

Geologic evidence shows plants next developed leaves and roots. Plants began using photosynthesis to supply their food, but still reproduced by dropping spores onto the ground that grew into new plants. Some of these early plants were known to be giant ferns. There are giant ferns that grow as tall as fifty feet still living today in tropical climates.

Giant Ferns

Following the ferns, fossil evidence shows that conifers were the next plants to grow and develop. These plants are called conifers because they grew cones (like pine cones) which were the first true seeds. The largest cones are female cones, and the smallest cones are male cones. The male cones release a yellow powder called pollen which is carried by the wind to the female cones. When pollen mixes with the spores in the female cones, seeds form.

Cones

The most recent type of plant to develop were the flowering plants. Flowering plants were more complex than any other plants that had grown previously, and came to be more diverse than any other plant family. Why?

As flowering plants were developing, insects and animals that could pollinate these flowering plants were developing as well. In fact, flowering plants and the insects and animals that pollinate them--their pollinators--seem to have developed in such a way that they both helped each other to survive throughout geologic time. How did geologists determine that flowers and their pollinators developed at the same time? Let's look at a specific example of how this could happen.

Birds are flowering plant pollinators. All birds see colors, but especially prefer red and other bright colors. A bird looking for nectar would choose brightly colored flowers rather than white flowers, and would choose flowers which are large enough for it to fit its beak into. As the bird feeds on the pollen, pollen sticks to its body and is carried to other flowers. Birds with long beaks would have more success in feeding on nectar that short-beaked birds. So long-beaked birds would survive and reproduce, and the number of long-beaked birds would increase. In a similar process, because the brightly colored flowers attract these long-beaked birds, they would also survive and reproduce because the long-beaked birds would choose them and therefore pollinate them. Over time both the population of long-beaked birds and brightly-colored flowers would increase because they help each other to survive. Because flowers and their pollinators help each other survive, over time their numbers would increase and they would grow and flourish everywhere. In this example, both the bright colors of the flowers and the long beaks of the birds are adaptations which affected the natural selection of these organisms as survivors.

If you look closely, you can tell what characteristics of other flowers and their pollinators have been helpful to their survival.

Butterflies have long, slender tongues, and will pollinate long, narrow flowers. However, butterflies still need a place to land while they are feeding on the flower's nectar, so these same flowers usually grow straight up and have clustered petals that give the butterfly a landing platform. In addition, butterflies seem to choose white, cream, yellow, pink and blue flowers in pastel colors.

Flowers that are open, shallow, and have a broad tube are preferred by bees and wasps. Why? Because bees and wasps have short tongues, and need easier access to the nectar. These flowers also have landing platforms, and usually have a sweet fragrance. Bees and wasps prefer white flowers, or brightly-colored yellow, orange, blue and violet flowers. They are not attracted to red flowers because many insects can see the color red.

Moths feed at night, and are therefore most attracted to white or pale-colored flowers that are more visible at night. Moths also prefer flowers with a strong, sweet smell. One moth, the Madagascar hawkmoth, has a tongue which is 22 centimeters long! This is the exact length of a species of orchid that grows in the same area--they help each other survive.

Many insects also prefer flowers that have nectar guides on the flower petals. These guides lead the insect to the source of the nectar, and different flower have very distinctive nectar guides. Many of these guides can only be seen under an ultraviolet light, a wavelength of light that can be seen by insect.

Hummingbirds are the most common bird pollinators. They choose large, tube-shaped flowers to match their long beaks. They choose flowers with lots of nectar because the hummingbirds needs lots of food energy to survive. The flower's anthers stick out above the petals so they are more likely to brush against the hummingbird and pick up pollen. Hummingbirds see red and yellow well, but have an underdeveloped sense of smell, so they often choose bright flowers with little fragrance.

As you have read, many characteristics of flowering plants are directly related to the insects and birds that pollinate them. The chart below lists some of those relationships:

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Last updated on December 22, 1999.