为了能够帮助更多的
Narrator: Listen to part of a lecture in a botany class.
Professor: When we talk about pollination ecology, we are talking about the relationship between a plant and its pollinator. From the plants’ perspective, the ideal pollinator is an animal that is under-fed, ready to eat and in a hurry. The pollinator, on the other hand, wants to remain well-fed with as little effort as possible.
These factors help drive the evolution of plants and their pollinators, both of which depend on this balanced and delicate relationship. Sometimes only certain insects or birds can pollinate certain plant species. So to really understand pollination ecology, both the flower and its pollinators must be studied.
Let’s start with flowers. There are several important factors associated with pollination: when and how often a plan flowers, how long the flowering cycle lasts, and the number of flowers that open at the same time. For example, flowering may coincide with the migration of a certain animal species that pollinates the plant, or producing many flowers at once may increase the number of pollinators a plant attracts.
Other characteristics of flowers are also important. Features such as color, scent and shape attract pollinators, as does the reward in the flower, the pollen or the nectar, that feeds the pollinator. For example, flowers that attract bats tend to be green or cream-colored, because visibility is important. Bats are practically blind, remember. And these flowers bloom at night when bats are active.
Now, there’s a flower in the Amazon rainforest called a royal water lily and the characteristics of its flowers change during the pollination process. The royal water lily uses color, temperature and scent to attract the beetles that pollinate it. When the flowers of the royal water lily first open up, when they first bloom, they are white. They also emit a strong odor and their temperature rises. Producing heat serves two purposes.
It magnifies the scent of the flower and it helps the beetles maintain their body temperature. When a beetle arrives at the flower, the flower closes around it for about 24 hours so that the beetle becomes covered with pollen. Then when the flower opens, its color changes to red and it cools down. When the beetle flies out, it carries the pollen to a different, heated, white, fragrant flower.
As you can see, plants go to a lot of trouble to attract attention. So what kind of attention are they attracting? And why? Well, sometimes flowers provide shelter for insects, a place to lay eggs for instance.
But usually the attraction is food: nectar and pollen. Nectar is mainly a sugar solution, while pollen is a grain made up of part of the plant’s cell structure. In both nectar and pollen production, quality and quantity vary over time. But they are always related to the needs of the pollinator.
You can see that the relationship between pollinators and plants are delicate, so any number of factors can disturb them. Human development is one. And agriculture is generally believed to be the most harmful.
It can fragment habitats in a variety of ways, reducing the number of pollinators, which in turn may reduce the number or size of the flowers, which of course affects the animals that feed on them. Exotic plant species not native to the area can move in and compete. Even bees brought in to pollinate crops can alter natural pollen dispersal systems of rainforest plants.
On the other hand, recent studies have shown that the disruption of one aspect of the pollination cycle doesn’t usually lead to the extinction of other species. It turns out that plant-pollinator relationships are more adaptable to change than we thought. So really it is hard to know just how agriculture affects the pollination of plants.
以上就是小编整理的精彩内容托福tpo34听力文本，希望可以帮助托福考生，更多精彩内容尽在，预祝托福考生取得理想成绩!