Chapter 3 Population 第三章 种群

1 Population Biology Concepts 种群生物学概念

1.1 Population Change 种群变动

种群的大小、密度、分布和年龄结构随着其生存环境中生物和非生物条件的变化而变化。

Populations in communities change in size, density, distribution, or age structure in response to changing biotic and abiotic conditions in their environment. These factors will include the availability of nutrients (nitrogen, phosphorus, water, sunlight), abundance of predators or competing species, or human activities.

1.2 Change in Population Size 种群大小的变动

种群大小的变化是比较容易计算的，一般用新增个体数量减去死亡和移居的个体数量。公式如下：

Change in Population Size =N = (birth + immigration) - (death + emigration)

有很多生物因素和非生物因素都在影响种群的大小。

1.2.1 Biotic Factors 生物因素

Some significant biotic factors that affect population growth include:

a. Food食物：Both the quantity and the quality of food are important. Snail, for example, cannot reproduce successfully in an environment low in calcium, no matter how much food there is, because they need this mineral for shell growth.

b. Predators捕食者：As a prey population becomes larger, it becomes easier for predators to find the prey. If the number of predators suddenly falls, the prey species might increase in number extremely quickly.

c. Competitors竞争者：Other organisms may require the same resources from the environment, and so resources from the environment and so reduce the growth of a population. For example, all plants compete for light. Competition for territory and for mates can drastically reduce the growth of individual organisms.

d. Parasites寄生物：Parasites may cause disease, and slow down the growth and reproductive rate of organisms within a population.

1.2.2 Important Abiotic Factors 重要的非生物因素

Important abiotic factors affecting population growth include:

a. Temperature气温：Higher temperatures speed up enzyme-catalysed reactions and increase growth.

b. Oxygen availability氧气有效度：Oxygen availability affects the rate of energy production by respiration.

c. Light availability光有效度：For photosynthesis. Light may also control breeding cycles in animals and plants.

d. Toxins and pollutants 毒素和污染物：Tissue growth can be reduced by the presence of, for example, sulphur dioxide, and reproductive success may be affected by pollutants such as oestrogen like substances.

1.2.3 Use Environmental Resistances to Manage Population利用环境阻力来控制人口

People use their understanding of environmental resistances to manage population. For example:

a. Predators are eliminated from farm situations．消除农场中的捕食者

b. More food is made available to domestic animals．提供更多食物给家畜

c. Nitrogen fertilisers and artificial light are used to boost plant growth．合理施肥，用人工光照来促进植物的生长

d. Predators may be used to control pests．用捕食者来控制害虫

e. Anaerobic conditions or low temperatures are used to prevent populations of microbes from consuming our food．用厌氧或低温条件抑制微生物生长

f. Competitors are eliminated from crops using pesticides．用农药来消除农作物的竞争者

1.3 Factors Affecting Population Change 影响种群变动的因素

种群大小和种群生长之间的关系（图1—3—1）：

● Distribution分布：种群分布在空间上可分为随机分布、群聚分布和均匀分布。

The three general patterns are random, clumped, and uniform. For most communities, populations living together in clumps or patches.

Reasons: Organisms gather around nutrients or resources that may also be in one area or organisms group together for protection, cooperative hunting, or possible collaborative care of their young. Some organisms may demonstrate a uniform or random distribution pattern but this is rare.

● Age structure 年龄结构：种群年龄结构指各年龄段个体数目占种群数目的比例。通过该年龄结构可以预测种群未来的大小变化（图1—3—2）。

The number of individuals in a population parsed into age cohorts by gender can predict the future change in size of the population. A majority of individuals in the pre-reproductive or reproductive age cohorts, is predictive of a population likely to grow. A majority of individuals in the post-reproductive years is predictive of a population likely to decrease in size.

a. Exponential (geometric) growth指数增长：Populations that grow at their intrinsic rate of increase (r), not limited by resources increase by a fixed rate each year.

b. Logistic growth逻辑斯蒂增长：After initial rapid growth the population size levels off due to declining resources or increasing competition.

c. Carrying capacity (K)承载能力：The upper limit for logistic growth—past this point the population will die back.

●Reproductive strategies 生殖策略：主要有两种，即r-strategist和K-strategist。

r-strategist: Numerous, small offspring; reach reproductive maturity early; fluctuate wildly above and below carrying capacity; adults are typically small in size; little to no parental care of offspring. (Survivorship: Early Loss Species)

K-strategist: Few, large offspring; reach reproductive maturity later; population stabilizes near carrying capacity; adults are typically large in size; give some type of parental care for offspring. (Survivorship: Late Loss Species)

二者的特点比较如表1—3—1所示：

2 Human Population 人口

2.1 Human Population Dynamics 人口动态

世界人口已经接近70亿（7 billion）且仍在不断增长。其中1/3的人口居住在中国和印度两大发展中国家，美国是第三大人口国家，拥有3亿（300 million）人。

2.1.1 Growth of the Human Population人口的不断增长

As with other organisms, the growth of the human population can be presented as a population growth curve. The number of humans increases, by reproduction, until the carrying capacity of the environment has been reached. Human have the ability to alter their environment to raise the carrying capacity.

Three major changes in human activities led to significant surges in the world population. As shown below.

人类活动的三个主要变化导致世界人口激增。如图1—3—3所示：

Agricultural revolution 农业革命：Human settlers became more efficient in their farming. More food became available and this part of environmental resistance to the human population was reduced.

Industrial revolution 工业革命：The development of machinery increased agricultural efficiency and improved housing conditions. More people earned enough money to be able to afford larger families, and the number of births increased.

Medical revolution医学革命：Improvements in sanitation and the control of infectious diseases reduced the number of deaths.Relative terms相关术语

Total fertility rate总生育率：the average number of children born to a woman during her lifetime

Replacement-level fertility替代水平生育：the average number of children a couple must bear to replace themselves in the population

The average is slightly higher than two children per couple because some children die before reaching reproductive age.

Infant mortality rate婴儿死亡率：the number of babies out of every 1,000 births who die before reaching their first birthday

Crude birth rate粗出生率：the number of births per 1,000 people in a population

Crude death rate粗死亡率：the number of deaths per 1,000 people in a population

Immigration迁入：the migration of people into a population

Emigration迁出：the migration of people out of a population

The Rule of 7070法则：For estimating the doubling time of a population. Divide 70 by the annual growth rate of the population expressed as a percent. The result will be the time (in years) required for the population to double.

2.1.2 Demographic Transition 人口过渡（图1—3—4）

人口过渡是指一个国家或地区的人口增长模型。一般一个国家都会从最初的高出生、高死亡、低增长阶段到高出生、低死亡、高增长阶段，最后进入低出生、低死亡、低增长阶段。

Demographic transition refers to a model for the population growth pattern of countries as they become industrialized nations. A country with a relatively small, stable population enters a demographic transition, and after many decades or centuries of rapid population growth, its population stabilizes at a significantly higher level.

2.1.3 Age-structure Diagrams 年龄结构图

人口年龄结构是将同一个国家或地区不同时间点上的人口年龄结构进行对比，从而推测该国家或地区的社会发展趋势和规律。

Age-structure diagrams are useful for determining the future change in size of a population. The number of females in the reproductive and pre-reproductive age groups is crucial because the total fertility rate of these women will determine the number of births in the population. Census figures show how many people of each group are present in a population. These figures may be plotted to give a population pyramid, as shown here（图1—3—5）.

年龄结构的作用

a．通过对比同一个国家或地区多年的人口年龄结构，可以预测该国家或地区的未来人口增长率。

By comparing the age-structure diagrams for one country over many years, it is possible to infer social changes that occurred in the country, and predict future changes to the population growth rate of the country.

b．通过对比不同国家或地区的人口年龄，可以推测出不同国家的社会状况、经济发展程度。

By comparing the age-structure diagrams of different countries to one another, it is possible to infer differences in the social conditions within the countries and the relative population growth rates of those countries.

2.1.4 Birth and Death Rates Affect Population Growth 出生率和死亡率影响人口增长

Both are expressed as percentages, so that:

Birth rate = number of births during year/original population at start of year ×100

Death rate = number of deaths during year/original population at start of year ×100

2.2 Population Size 人口规模

2.2.1 Human Population Growth is a Barrier to Sustainable Resource Use 人口增长阻碍了资源的可持续利用

Human population growth is responsible for most of the environmental problems confronting the world today.

2.2.2 Empowerment of Women 赋权于女性

Empowerment of women is an important strategy for slowing the rapid population growth in much of the developing world.

●Population in China 中国人口

a. One-child policy 独生子女政策

Implemented during the 1970s, one-child policy decreased the country's total fertility rate by more than one-third, from nearly six, to less than two children per woman in approximately 35 years.

b. Larger middle class 中产阶级的扩增

With slower population growth, and an increased GNP, the per capita wealth in China has grown, adding hundreds of millions of new middle class citizens to the world. The lifestyles of more affluent individuals require more resources to maintain or keep pace with their social status.

c. Male-dominant population 重男轻女

Due to cultural preferences for male children, Chinese population is male-dominant.

●Population in India 印度人口

a. Larger middle class中产阶级的扩增

With increased industrialization, participation in the high-tech industry and a population over one billion, India is adding tens of millions of people annually to the middle class.

b. Living in poverty生活贫困

In contrast to China, the population growth of India has not slowed significantly and the number of people living in poverty continues to grow. A population living in poverty comes with many environmental costs, including the degradation of forests, fisheries, soils, and waterways as a result of desperate attempts to survive.

2.3 Impacts of Population Growth人口增长的影响

2.3.1 Food Distribution 食物分布

More than enough food is produced to meet the basic nutritional needs of every person on earth; however, the areas of food production are unevenly distributed amongst the population.

2.3.2 Hunger 饥荒

Several factors contribute to malnutrition, for example: poverty, droughts, limited carrying capacity, political instability and wars, pestilence and foreign investment.

2.3.3 Resource Use and Habitat Destruction 资源利用和生境破坏

Measure net primary productivity.

Estimate how much impact humans have had on Earth.

Examine finite resources and from that draw conclusions on increasing productivity.

●Several factors may influence resource utilization．影响资源利用的因素各种各样。

For example：

a. Energy resources

b. Environmental degradation

c. Carrying capacity

d. Extinction of animal and plant species

e. Population size

f. Population density

g. Poverty

h. Technological development

2.3.4 Infectious Diseases 传染病（表1—3—2）

传染病的传播直接影响了人口密度和人口数量。

Infectious diseases spread more quickly in densely populated areas. The modern city is an ideal environment for the spread of old (influenza, cholera, and the common cold) and newly emergent (SARS, HIV/AIDS, and West Nile fever) diseases. An outbreak of an infectious disease that is limited to one area or region is known as an epidemic. However, if this disease spreads globally it is referred to as a pandemic.