环境科学交叉关系学科——7章重点句和词汇

环境科学交叉关系学科——7章重点句和词汇
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第7章种群原理 Population Principles
A population can be defined as a group of individuals of the same species inhabiting an area。

Some important ways in which populations differ include natality (birthrate)，mortality (death rate)，sex ratio, age distribution, growth rates, density， and spatial distribution.
In human populations， natality is usually described in terms of the birthrate, the number of individuals born per l000individuals per year。

In human population studies, mortality is usually discussed in terms of the death rate，the number of people who die per 1000 individuals per year。

The population growth rate is the birthrate minus the death rate。

The sex ratio refers to the relative numbers of males and females。

The age distribution， the number of individuals of each age in the population, greatly influences the population growth rate.
Population density is the number of organisms per unit area。

When the population density is too great，all individuals within the population are injured because they compete severely with each other for necessary resources.
The carrying capacity of an area is the number of individuals of a species that can be maintained in an area， over time, without harming the habitat。

The combination of factors that sets the carrying capacity for an area is called environmental resistance.
For most populations, four categories of limiting factors are recognized as components of environmental resistance that set the carrying capacity。

These are： (1) the availability of raw materials，(2） the availability of energy, (3） the accumulation of waste products and their means of disposal， and (4） interactions among organisms。

K—strategists are organisms that typically reach a stable population as the population reaches the carrying capacity。

K-strategists usually occupy relatively stable environments and tend to be large organisms that have relatively long lives, produce few offspring，and provide care for their offspring。

The r—strategist is typically an organism that exploits unstable environments。

Typically， r-strategists are small organisms that have a short life, produce many offspring，and do not reach a carrying capacity。

Floods, droughts，fires, extreme cold, and similar events may affect the carrying capacity of an area, thus causing fluctuations in
population size。

Epidemic disease or increased predation may also lead to populations that vary in size from year to year。

Many endangered species have reduced populations because their normal environment has been altered either naturally or as a result of human activity。

Although local human populations often show fluctuations，the worldwide human population has increased continually for the past several hundred years。

Humans have been able to reduce environmental resistance by eliminating competing organisms, increasing food production， and controlling disease organisms。

The current worldwide rate of annual increase of about 1.3 percent will double the world human population in about 54 years. What does this very rapid rate of growth mean to the human species? As a species，humans are subject to the same limiting factors as all other specie.
Food production is becoming a limiting factor for some segments of the world's human population。

Malnutrition is a serious problem in many parts of the world because sufficient food is not available. Currently, about l billion people (one—sixth of the world's population）suffer from a lack of adequate food。

Currently， the world's human population depends on fossil fuels to raise food, modify the environment， and move from place to place。

When energy prices increase，much of the world’s population is placed injeopardy because incomes are not sufficient to pay the increased costs for energy and other essentials. New，less disruptive methods of harnessing this energy must be developed to support an increasing population.
Waste disposal is the third factor determining the carrying capacity for humans. Most pollution is, in reality, the waste product of human activity.
Lack of adequate sewage treatment and safe drinking water causes large numbers of deaths each year。

Some people are convinced that disregard for the quality of our environment will be a major limiting factor。

In any case, it makes good sense to control pollution and to work toward cleaning our environment.
The fourth factor that determines the carrying capacity of a species is interaction with other organisms。

We need to become aware that we are not the only species of importance。

When we convert land to meet our needs， we displace other species from their habitats. Many of these displaced organisms are not able to compete with us successfully and must migrate or become extinct。

What today seems like an unimportant organism, one that we could
easily do without， may someday be seen as an important link to our very survival.
It is also important to recognize that many organisms provide services that we enjoy without thinking about them。

People make decisions based on history, social situations, ethical and religious considerations，and personal desires。

People in all fields need to understand that the cause of the population problem has both biological and social components if they are to successfully develop strategies for addressing it。

As with all K—strategist species，when the population increases, density—dependent limiting factors will become more forceful。

No one knows what the ultimate human population size will be or what the most potent limiting factors will be，but most agree that we are approaching the maximum sustainable human population.
If the human population continues to increase, eventually the amount of agricultural land available will not be able to satisfy the demand for food.
Summary：
A population is a group of organisms of the same species that inhabits an area。

Population growth is determined by the combined effects of the birthrate and death rate.
The carrying capacity is determined by many limiting factors that are collectively known as environmental resistance. The four major categories of environmental resistance are available raw materials, available energy， disposal of wastes, and interactions among organisms。

K-strategists typically are large， long-lived organisms that reach a stable population at the carrying capacity.
The human population is increasing at a rapid rate. The Earth’s ultimate carrying capacity for humans is not known. The causes for human population growth are not just biological but also social, political, philosophical， and theological.
Key Terms： birthrate 出生率carrying capacity 容纳量death rate 死亡率environmental resistance 环境阻力K—strategists K-策略生物limiting factor 限制因子mortality 死亡率natality出生率population 种群population density 种群密度 population growth rate 种群生长率sex ratio 性别比
Review Questions：
2. List three characteristics populations might have。

5. List four factors that could determine the carrying capacity of an animal species.
8。

How do r-strategists and K-strategists differ？
9. As the human population continues to increase， what might happen to other species？。