托福official34听力lecture3 Plants And Pollinators原文解析+翻译音频

[00:00.00]NARRATOR: Listen to part of a lecture in a botany class.[00:04.49]FEMALE PROFESSOR: When we talk about pollination ecology, we are talking about the relationship between a plant and its pollinator. [00:12.86]From the plants' perspective, the ideal pollinator is an animal that is under-fed, ready to eat and in a hurry. [00:21.13]The pollinator, on the other hand, wants to remain well-fed with as little effort as possible.
[00:27.10]These factors help drive the evolution of plants and their pollinators, both of which depend on this balanced and delicate relationship. [00:35.86]Sometimes only certain insects or birds can pollinate certain plant species. [00:41.82]So to really understand pollination ecology, both the flower and its pollinators must be studied.[00:49.01]Let's start with flowers. [00:51.47]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. [01:05.78]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.[01:20.88]Other characteristics of flowers are also important. [01:24.11]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. [01:34.58]For example, flowers that attract bats tend to be green or cream-colored, because visibility is important. [01:42.89]Bats are practically blind, remember. [01:45.23]And these flowers bloom at night when bats are active.
[01:48.86]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. [01:59.48]The royal water lily uses color, temperature and scent to attract the beetles that pollinate it. [02:06.39]When the flowers of the royal water lily first open up, when they first bloom, they are white. [02:12.34]They also emit a strong odor and their temperature rises. [02:16.94]Producing heat serves two purposes.
[02:20.18]It magnifies the scent of the flower and it helps the beetles maintain their body temperature. [02:26.65]When a beetle arrives at the flower, the flower closes around it for about 24 hours so that the beetle becomes covered with pollen. [02:35.67]Then when the flower opens, its color changes to red and it cools down. [02:41.45]When the beetle flies out, it carries the pollen to a different, heated, white, fragrant flower.[02:48.51]As you can see, plants go to a lot of trouble to attract attention.[02:53.19] So what kind of attention are they attracting? And why? [02:57.58]Well, sometimes flowers provide shelter for insects, a place to lay eggs for instance.
[03:04.00]But usually the attraction is food: nectar and pollen. [03:07.74]Nectar is mainly a sugar solution, while pollen is a grain made up of part of the plant's cell structure. [03:15.46]In both nectar and pollen production, quality and quantity vary over time. [03:21.44]But they are always related to the needs of the pollinator.[03:24.82]You can see that the relationship between pollinators and plants are delicate, so any number of factors can disturb them. [03:32.79]Human development is one. And agriculture is generally believed to be the most harmful.
[03:39.11]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. [03:51.49]Exotic plant species not native to the area can move in and compete. [03:56.81]Even bees brought in to pollinate crops can alter natural pollen dispersal systems of rainforest plants.
[04:04.39]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. [04:14.66]It turns out that plant-pollinator relationships are more adaptable to change than we thought. [04:20.65]So really it is hard to know just how agriculture affects the pollination of plants.