大学英语精读听力第四册 unit2

[00:00.00]Unit Two
[00:21.73]Text
[00:23.22]Is there anything we can learn from deer?
[00:26.88]During the "energy crisis" of 1973-1974
[00:31.74]the writer of this essay was living in northern Minnesota
[00:35.29]and was able to observe how deer survive when winter arrives.
[00:39.39]The lessons he learns about the way deer conserve energy turn out applicable to our everyday life
[00:46.29]DEER AND THE ENERGY CYCLE      Aaron N. Moen
[00:51.88]Some persons say that love makes the world go round.
[00:55.85]Others of a less romantic and more practical turn of mind
[00:59.43]say that it isn't love; it's money.
[01:02.17]But the truth is that it is energy that makes the world go round.
[01:06.22]Energy is the currency of the ecological system
[01:09.56]and life becomes possible only when food is converted into energy,
[01:14.19]which in turn is used to seek more food to grow, to reproduce and to survive.
[01:20.48]On this cycle all life depends.
[01:23.33]It is fairly well known that wild animals survive
[01:27.12]from year to year by eating as much as they can during times of plenty,
[01:31.27]the summer and fall, storing the excess, usually in the form of fat,
[01:36.42]and then using these reserves of fat
[01:38.98]to survive during the hard times in winter when food is scarce.
[01:43.58]But, it is probably less well known that even with their stored fat,
[01:48.04]wild animals spend less energy to live in winter than in summer.
[01:52.33]A good case in point is the white-tailed deer.
[01:55.98]Like most wildlife, deer reproduce,
[01:59.14]grow,and store fat in the summer and fall when there's plenty of nutritious food available
[02:04.81]A physically mature female deer in good condition who has conceived in November
[02:10.09]and given birth to two fawns during the end of May or first part of June,
[02:14.82]must search for food for the necessary energy
[02:17.77]not only to meet her body's needs but also to produce milk for her fawns.
[02:23.10]The best milk production occurs at the same time that new plant growth is available.
[02:28.66]This is good timing,because milk production is an energy consuming process--
[02:33.91]it requires a lot of food.
[02:36.29]The cost can not be met unless the region has ample food resources.
[02:41.36]As the summer progresses and the fawns grow,
[02:45.20]they become less dependent on their mother's milk
[02:47.92]and more dependent on growing plants as food sources.
[02:51.47]The adult males spend the summer growing antlers and getting fat.
[02:55.93]Both males and females continue to eat high quality food in the fall
[03:00.56]in order to deposit body fat for the winter.
[03:03.80]In the case of does and fawns,
[03:06.23]a great deal of energy is expended either in milk production or in growing,
[03:11.29]and fat is not accumulated as quickly as it is in full grown males.
[03:16.26]Fat reserves're like bank accounts to be drawn on in the winter when food supplies are limited
[03:22.42]and sometimes difficult to reach because of deep snow.
[03:25.95]As fall turns into winter,other changes take place.
[03:30.00]Fawns lose their spotted coat.
[03:32.27]Hair on all the deer becomes darker and thicker.
[03:35.67]The change in the hair coats is usually complete by September
[03:39.90]and maximum hair depths are reached by November or December when the weather becomes cold
[03:45.57]But in addition, nature provides a further safeguard to help deer survive the winter--
[03:51.34]an internal physiological response which lowers their metabolism,
[03:56.49]or rate of bodily functioning,
[03:58.42]and hence slows down their expenditure of energy.
[04:01.97]The deer become somewhat slow and drowsy.
[04:04.72]The heart rate drops.
[04:06.52]Animals that hibernate practice energy conservation to a greater extreme than deer do.
[04:12.40]Although deer don't hibernate,
[04:14.33]they do the same thing with their seasonal rhythms in metabolism.
[04:18.48]Deer spend more energy and store fat in the summer and fall when food is abundant,
[04:24.28]and pend less energy and use stored fat in the winter when food is less available.
[04:29.95]When the "energy crisis" first came in 1973-1974,
[04:36.50]I was living with my family in a cabin
[04:38.88]on the edge of an area where deer spend the winter in northern Minnesota,
[04:43.19]observing the deer as their behavior changed
[04:45.93]from more activity in summer and fall to less as winter progressed,
[04:50.29]followed by an increase again in the spring as the snow melted.
[04:54.97]It was interesting and rather amusing to listen to the advice given on the radio:
[05:00.04]"Drive only when necessary," we were told.
[05:02.78]"Put on more clothes to stay warm,and turn the thermostat on your furnace down."
[05:07.93]Meanwhile we watched the deer reduce their activity,
[05:11.61]grow a winter coat of hair,
[05:13.46]and reduce their metabolism as they have for thousands of years.
[05:17.59]It's biologically reasonable for deer to reduce their cost of living
[05:22.09]to increase their chances of surviving in winter.
[05:25.27]Not every winter iscritical for deer ofcourse.
[05:28.54]If the winter has light snow, survival and productivity next spring will be high.
[05:33.58]But if deep snows come and the weather remains cold for several weeks,
[05:37.84]then the deer must spend more energy to move about,
[05:41.29]food will be harder to find,
[05:43.22]and they must then depend more on their fat reserves to pull them through.
[05:47.66]If such conditions go on for too long some will die,
[05:51.58]and only the largest and strongest are likely to survive.
[05:55.63]That is a fundamental rule of life for wild,
[05:58.87]free wandering animals such as deer.
[06:01.29]Yes, life -- and death, too -- is a cycle that goes round and round,
[06:06.05]and when animals die their bodies become food for other life forms to use
[06:10.78]by converting them into energy. And the cycle continues.