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  • General

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  • 人口规模

    A flock of snow geese foraging in wetland areas of Kenai National Wildlife Refuge.

     

    How many geese are the right number for this area?
    ::这个区域有多少只鹅是正确的数字?

    As many as can survive and have healthy offspring! The figure above shows a flock of  snow  geese at the Kenai National Wildlife Refuge. Their  population  will tend to grow as big as it can for the resources it needs. Once it is too large, some of its members will die off. This keeps the population size at the right number.
    ::尽可能多的人能够生存并有健康的后代! 上图显示了肯奈国家野生动物保护区的一群雪雁。 他们的人口将尽可能增长, 以获得它所需要的资源。 一旦人口过多, 有些成员就会死亡。 这使得人口数量保持在正确的数量上。

    How Populations Grow
    ::人口增长情况

    A population usually grows when it has what it needs. If there’s plenty of food and other resources, the population will get bigger. Refer to the table below ( Table   ); it shows how a population of bacteria grew. A single bacteria cell was added to a container of  nutrients . Conditions were ideal. The bacteria divided every 30 minutes. After just 10 hours, there were more than a million bacteria! Assume the bacteria population keeps growing at this rate. How many bacteria will there be at 10.5 hours? Or at 12 hours?
    ::人口通常在拥有所需的食物和其他资源时增长。 如果有充足的食物和其他资源,人口就会增加。 参考下表(表 ) ; 它显示了细菌人口是如何增长的。 将一个单一细菌细胞添加到营养物容器中。 条件很理想。 每30分钟细菌就分裂一次。 仅仅10小时后就有100多万细菌! 假设细菌人口以这种速度增长。 有多少细菌将在10.5小时或12小时出现?

    Time (hours) Number of Bacteria
    0 1
    0.5 2
    1.0 4
    1.5 8
    2.0 16
    2.5 32
    3.0 64
    3.5 128
    4.0 256
    4.5 512
    5.0 1,024
    5.5 2,048
    6.0 4,096
    6.5 8,192
    7.0 16,384
    7.5 32,768
    8.0 65,536
    8.5 131,072
    9.0 262,144
    9.5 524,288
    10 1,048,576

    Population Growth Rate
    ::人口增长率

    The  population growth rate  is how fast a population is growing. The letter  r  stands for the growth rate. The growth rate equals the number of new members added to the population in a  year  for each 100 members already in the population. The growth rate includes new members added to the population and old members removed from the population. Births add new members to the population. Deaths remove members from the population. The formula for population growth rate is:
    ::人口增长率是人口增长速度的快。 字母 r 表示增长率。 增长率等于每100名已经在人口中的成员在一年内增加的新成员数量。 增长率包括人口增加的新成员和从人口中剔除的老成员。 出生增加了新的成员。 死亡使人口从人口中消失。 人口增长率的公式是:

    r  =  b - d , where
    ::r = b - d, 其中

    b  = birth rate (number of births in 1 year per 100 population members)
    d  = death rate (number of deaths in 1 year per 100 population members)

    If the birth rate is greater than the death rate,  r  is positive. This means that the population is growing bigger. For example, if  b  = 10 and  d  = 8,  r  = 2. This means that the population is growing by 2 individuals per year for every 100 members of the population. This may not sound like much, but it’s a fairly high rate of growth. A population growing at this rate would double in size in just 35 years!
    ::如果出生率高于死亡率,r是正数。这意味着人口正在增加。例如,如果b=10和d=8,r=2,则人口每年每100名人口增加2人。这听起来可能不怎么好,但增长率相当高。 以这一速度增长的人口在35年内会翻一番!

    If the birth rate is less than the death rate,  r  is negative. This means that the population is becoming smaller. What do you think might cause this to happen?
    ::如果出生率低于死亡率,r为负值。这意味着人口正在减少。你认为是什么原因导致这种情况发生?

    Carrying Capacity
    ::承承能力

    A population can’t keep growing bigger and bigger forever. Sooner or later, it will run out of things it needs. For a given  species , there is a maximum population that can be supported by the environment. This maximum is called the  carrying capacity . When a population gets close to the carrying capacity, it usually grows more slowly ( Figure   ). When the population reaches the carrying capacity, it stops growing.
    ::人口不可能永远长大。 它迟早会耗尽它需要的东西。 对于特定物种来说,环境可以支撑的最大数量。 这个最大数量被称为承载能力。 当人口接近承载能力时,它通常会增长更慢(图 ) 。 当人口达到承载能力时,它就会停止增长。

    Graph illustrating population growth over time, highlighting rapid growth and stabilization at carrying capacity.

     

    A population can’t get much larger than the carrying capacity. What might happen if it did?
    ::人口不可能比承受能力大得多。 如果有的话会怎样呢?

     

    Summary
    ::摘要

    • A population will grow as long as it has what it needs.
      ::只要人口拥有它所需要的,人口就会增长。
    • The carrying capacity of an environment is reached when the number of births equal the number of deaths.
      ::当出生人数与死亡人数相等时,环境的承受能力就达到。
    • A limiting factor determines the carrying capacity for a species.
      ::限制因素决定物种的承载能力。

    Review
    ::回顾

    1. What happens if a population exceeds its carrying capacity?
      ::如果人口超过其承载能力,会发生什么情况?
    1. Explain how a single bacterium can grow to a population of more than a million 10 hours later.
      ::解释一个单一细菌如何在10小时后成长到超过100万人口。
    1. What happens if the birth rate in a population is more than the death rate? What happens if it is less?
      ::如果人口出生率高于死亡率,会怎样?如果人口出生率低于死亡率,会怎样呢?如果人口出生率低于死亡率,会怎样呢?