Download 河 北 科 技 大 学 教 案 用 纸

河 北 科 技 大 学 教 案 用 纸
第
次课
7
2
学时
上次课复习
1. What is succession?
2. Describe Major Types of Terrestrial Climax Communities
3. Describe Major Aquatic Ecosystems
本次课题（或教材章节题目）
： Ch7
Populations
教学要求： 了解种群的特征和成长曲线；熟悉影响种群的限制因素；掌握种群繁殖策略和种群
波动
重
点：种群的限制因素
难
点：群繁殖策略和种群波动
教学手段及教具：利用多媒体进行课堂讲授，图文并茂，增加认知的直观性；进行课堂讨论，
活跃课堂气氛。
讲授内容及时间分配：
Revision
7.1 Population Characteristics
7.2 A Population Growth Curve
7.3 Factors That Limit Population
7.4 Categories of Limiting Factors
7.5 Carrying Capacity
7.6 Reproductive Strategies and Population Fluctuations
7.7 Human Population Growth
Summary
3 min
22min
5 min
10min
10min
10min
22min
5min
3min
课后作业
任选课后讨论题，完成 50-80 字英文短文。
参考资料
《Environmental Science》 Andrew R.W.Jackson．世界图书出版社，2001．
《Environmental Science》 William P.Cunningham．McGraw-Hill，1997．
注：本页为每次课教案首页
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一、 Population Characteristics
1. A population can be defined as a group of individuals of the same species inhabiting an area.
Influence factors:
natality and mortality
immigration and emigration
Population increased by: ?
Population decreased by: ?
2. Natality and mortality
Natality: the number of individuals added to the population through reproduction over a particular time
period.
Asexual reproduction: bacteria and other tiny organisms, sponges, jellyfish, worms, some insects and lizards
Sexual reproduction
Mortality: the number of deaths in a population over a particular time period.
For human: birthrate and death rate
Effect of Birthrate and Death Rate on Population Size For a population to grow, the birthrate must exceed the
death rate for a period of time. These three human populations illustrate how the combined effects of births
and deaths would change population size if birthrates and death rates were maintained for a five-year period.
(a) The Dall sheep is a large mammal that produces relatively few young. Most of the young survive, and
more susceptible to predation and disease.
(b) The curve shown for the white-crowned sparrow is typical of that for many kinds of birds. After a
period of high mortality among the young the mortality rate is about equal fro all ages of adult birds.
(c) Many small animals and plants produce enormous numbers of offspring. Mortality is very high in the
younger individuals, and few individuals reach old age.
3. Sex Ratio
Sex ratio refers to the relative numbers of males and females. (Many kinds of organisms, such as
earthworms and most plants, have both kinds of sex organs in the same body; sex ratio has no meaning
for these species.)
Types: ???
4. Age distribution
Age distribution refers to the number of individuals of each age in the population.
For example, ecologists may divide a population into pre-reproductive, reproductive, and
post-reproductive ages.
Individuals in the first category have the potential to produce offspring when they mature. Together
with the actually and potentially reproducing members in the second category, we count them as part of the
population reproductive base.
Types:
5. population density
 The number of individuals of a population that are living in a specified area or volume.
 Types:
 Density independent forces: ???
-Climate
-Topography
-Latitude
-Altitude
-Rainfall
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-Sunlight
In sum: abiotic factors
二、A Population Growth Curve
1. Biotic potential
Biotic Potential - Inherent reproductive capacity. Generally, biotic potential is much above replacement level.
Natural tendency for increase. All living populations follow an exponential growth curve.
Biotic Potential The ability of a species to reproduce greatly exceeds the number necessary to replace those
who die. Here are some examples of the prodigious reproductive abilities of some species
2.
Logistic
-Lag stage: the population grows very slowly because there are few births, since the process of reproduction
and growth of offspring takes time.
-Exponential growth stage: offspring begin to mate and have young, the parents may be producing a
second set of offspring. Since more organisms now are reproducing, the population begins to increase at an
accelerating rate.
-Stable equilibrium stage: the death rate and the birthrate will come to equal one another, and the
population will stop growing and reach a relatively stable population size.
三、 Factors That Limit Population Size
1. Extrinsic and intrinsic limiting factors
Some factors that control populations come from outside the population and are known as extrinsic
limiting factors.
However, the populations of many kinds organisms appear to be regulated by factors from within the
populations themselves, such limiting factors are called intrinsic limiting factors.
2. Density-dependent and density-independent limiting factors
Density-dependent limiting factors are those that become more effective as the density of the population
increases: predators.
Density-independent limiting factors are population-controlling influences that are not related to the
density of the population: rainstorm.
四、Categories of Limiting Factors
1.Limiting factors
The availability of raw materials
The availability of energy
The accumulation of waste products
Interactions among organisms
2. A Bacterial Growth Curve The initial change in population size follows a typical population growth curve
until waste products become lethal. The buildup of waste products lowers the carrying capacity. When a
population begins to decline, it enters the death phase.
五、Carrying Capacity
The carrying capacity is the maximum sustainable population for a area.
六、 Reproductive Strategies and Population Fluctuations
1. Strategists
 r-strategists
- Exploits unstable environments
- Small organisms that have a short life, produce many offspring, and do not reach a carrying
capacity
- The reproductive strategy of r-strategists is to expend large amounts of energy producing many
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offspring but to provide limited care (often none) for them. Consequently, there is high mortality
among the young.
 K-strategists
- typically reach a stable population as the population reaches the carrying capacity.
- 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.
- Their reproductive strategy is to invest a great deal energy in producing a few offspring that have
good chance of living to reproduce.
r-strategist
K-strategist
Climate needed
Variable and/or unpredictable
Fairly
constant
predictable
Mortality
Often catastrophic
Seldom catastrophic
Population size
Variable through time, seldom Fairly constant, approaches
reaching
carrying
capacity, carrying
capacity
and
disequilibrial
equilibrium
Ability to compete
Low
Selection favors
Rapid
development,
early Slow
development,
reproduction, small body size, postponed
reproduction,
single reproductive effort
large body size, repeated
reproduction
Length of life
Short, usually <1year
Long, usually >1 year
Leads to
High productivity
High efficiency
and/or
High
七、Human Population Growth
Major reason for increasing human population growth rate is an increase in medical care, and a
consequential decrease in death rates.
Doubling Time of a population (years) :
70 / Population Growth Rate (%)
( 70 / 2.0% = 35 years )
Doubling Time for the Human Population This graph shows the relationship between the rate of annual
increase in percent and doubling time. A population growth rate of 1 per year would result in the doubling of
the population in about 70 years. A population growth rate of 3 percent per year would result in a population
doubling in about 23 year.
The Historical Human Population Curve From A. D. 1800 to A. D. 1930, the number of humans doubled
from 1 billion to 2 billion and then doubled again by 1975 and could double again by the year 2025. How
long can this pattern continue before the Earth’s ultimate carrying capacity is reached?
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