章节大纲

  • 常规

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  • 人口增长

    What you will learn
    ::你会学到什么

    • What is the population growth rate
      ::人口增长率是多少
    • Factors affecting the population growth rate
      ::影响人口增长率的因素

    Vintage luggage and baskets symbolizing the journey of immigrants at Ellis Island.

    What would old luggage have to do with population growth?
    ::旧行李与人口增长有什么关系?

    Moving into an area, or immigration , is a key factor in the growth of . Shown above is actual vintage luggage left by some of the millions of immigrants who came through Ellis Island and into the United States.
    ::进入一个地区,或移民,是增长的关键因素。 上面显示的是通过埃利斯岛进入美国的数百万移民留下的实际旧行李。

    Population Growth
    ::人口增长

    Populations gain individuals through births and immigration. They lose individuals through deaths and emigration . These factors together determine how fast a population grows.
    ::人口通过出生和移民而增加,因死亡和移民而丧失,这些因素加在一起决定人口增长速度。

    Population Growth Rate
    ::人口增长率

    Population growth rate ( r ) is how fast a population changes in size over time. A positive growth rate means a population is increasing. A negative growth rate means it is decreasing. The two main factors affecting population growth are the birth rate ( b ) and death rate ( d ). Population growth may also be affected by people coming into the population from somewhere else ( immigration , i ) or leaving the population for another area ( emigration , e ). The formula for population growth takes all these factors into account.
    ::人口增长率(r)是人口规模随时间变化的速度。正增长率意味着人口在增长。负增长率意味着人口在下降。影响人口增长的两个主要因素是出生率(b)和死亡率(d),人口增长也可能受到从别处进入人口(移民,i)或离开人口去另一个地区(移民,e)的影响。人口增长公式考虑到所有这些因素。

    r = ( b + i ) - ( d + e )
    ::r = (b + i) - (d + e)

    • r = population growth rate
      ::r = 人口增长率
    • b = birth rate
      ::b = 出生率
    • i = immigration rate
      ::i = 移民比率
    • d = death rate
      ::d = 死亡率
    • e = emigration rate
      ::e = 外迁率

    Dispersal
    ::分散

    Other types of movements may also affect population size and growth. For example, many have some means of dispersal . This refers to offspring moving away from their parents. This prevents the offspring from competing with the parents for resources such as light or . For example, dandelion seeds have “parachutes.” They allow the wind to carry the seeds far from the parents (see Figure ).
    ::其他类型的迁移也可能影响人口规模和增长,例如,许多类型的迁移具有某种分散手段,这是指后代离开父母,这妨碍后代与父母争夺资源,例如光或光。例如,dandelion种子有“降落伞 ” 。 它们允许风把种子运到远离父母的地方(见图 ) 。

    Dandelion puff releasing seeds into the air, illustrating seed dispersal by wind.
    Dandelion Seeds. These dandelion seeds may disperse far from the parent plant. Why might this be beneficial to both parents and offspring?

    Migration
    ::移徙移徙移徙

    is another type of movement that changes population size. Migration is the regular movement of individuals or populations each year during certain seasons. The purpose of migration usually is to find food , mates, or other resources. For example, many northern hemisphere migrate thousands of miles south each fall. They go to areas where the weather is warmer and more resources are available (see Figure ). Then they return north in the spring to nest. Some , such as elk, migrate vertically. They go up the sides of mountains in spring as snow melts. They go back down the mountain sides in fall as snow returns.
    ::移徙是个人或人口在特定季节每年的正常流动。移徙的目的通常是寻找食物、伴侣或其他资源。例如,许多北半球每年秋天向南迁徙数千英里。它们去的是天气比较暖和、资源比较丰富的地区(见图)。然后,它们返回春天的北边筑巢。有些,例如鹿,垂直移徙。随着雪雪的融化,它们会从山的两边向上移动。随着雪的回流,它们会从山的两边向下游。

    Map showing migration routes of Swainson’s hawks between North and South America.
    Swainson’s hawks migrate from North to South America and back again each year. This map shows where individual hawks have been identified during their migration.

     

     

     

     

    Summary
    ::摘要

    • Population growth rate is how fast a population changes in size over time.
      ::人口增长率是人口规模随时间变化的速度。
    • Population growth is determined by rates of birth, death, immigration, and emigration.
      ::人口增长取决于出生、死亡、移民和移民的增长率。

    Review
    ::回顾

    1. Define immigration and emigration.
      ::界定出入境的定义。
    2. What is migration? Give an example.
      ::移徙是什么?举个例子。
    3. Write the formula for the population growth rate. Identify all the variables.
      ::写入人口增长率的公式。 确定所有变量 。
    4. What is dispersal? State why dispersal of offspring away from their parents might be beneficial
      ::什么是分散?国家为什么将子女从父母分离出去可能有益?