Population Biology 

种群∶一个区域内的所有属于同一物种的相同生物

Population density: the number of individuals of a population that inhabit a certain area

种群变动∶

Change in population size (N)=(birth + immigration)-(death +immigration)

生物因素∶ food, predators, competitors, parasites

非生物因素∶temperature, oxygen availability, light availability, toxins and pollutants

控制种群数量∶

1. Predators are eliminated 

2. More food

3. Nitrogen fertilizers and artificial light 

4. Predators

5. Anaerobic conditions or low temperatures 

6. Pesticides

影响种群变动的因素∶

1.Distribution

Types: random, clumped (most), and uniform

Reasons: gather around nutrients or resources; group together for protection, cooperative hunting, care the young

2. Age structure

Pre-reproductive & reproductive → grow

Post-reproductive → decrease

3. Reproductive strategies

Population growth model： 

Exponential(geometric) growth:

Populations that grow at their intrinsic rate of increase (r), not limited by resources. 

J-shaped curve

Logistic growth:

A population whose growth is initially exponential, but slows as the population approaches the carrying capacity of the environment (K).

Carrying capacity (K): the upper limit of logistic growth.

S-shaped curve

Population cycle:

Boom-and-bust cycle

The rapid changes may be linked to predictable cycles in the environment.

Predator-prey cycle

The predator population changes after the prey population does.

Ecological footprint: the environmental impact of a population

IPAT model: I(the total impact)=P(population size)×A(affluence)×T(level of technology)

物种的濒危和灭绝∶

Extinction > endangered > threatened

Background extinction rate: the natural rate of extinction

Destruction of animal and plant habitats:

1. Habitat fragmentation when building roads and cities

2. Habitat degradation when adding pollutants to the environment 

3. Invasive species

4. Direct hunting or overexploitation for animal products

Biodiversity hot spot: a highly diverse region that faces severe threats

相关法案∶

Marine Mammal Protection Act: protect marine mammals from falling below their optimum sustainable population levels

Endangered Species Act Program: prohibited the commerce of those species considered to be threatened 

CITES: bans the capture, exportation or sale of endangered and threatened species

HUMAN POPULATION

人口激增的原因∶

Agricultural revolution: more food becomes available

Industrial revolution: the development of machinery increases agricultural efficiency and improved housing conditions

Medical revolution: improvements in sanitation and the control of diseases reduce the mortality rate

人口变动的因素∶

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

Replacement-level fertility: slightly higher than two children per couple

Infant mortality rate: the number of babies out of every 1000 births who die before 1 year old

Crude birth/death rate: the number of births/deaths per 1000 people in a population

Immigration: foreigners move into 

Emigration: residents more out

The Rule of 70: 70/ annual growth rate (%)= doubling time

注意如果题目中给的是 crude rate，先把干分率换为百分率，然后进行计算。

影响生育率的因素∶

The availability of birth control

The demand for children in the labor force 

The base level of education for women

The existence of public and/or private retirement systems 

The population's religious beliefs, culture, and traditions

Demographic transition 人口过渡

Pre-industrial∶高出生率，高死亡率，低自然增长率

Transitional∶ 高出生率，死亡率开始下降，自然增长率和总人口大大增加

Industrial∶出生率开始下降，死亡率降到更低，自然增长率减慢但仍为正数，总人口缓慢增加

Post-industrial∶出生率继续下降，死亡率保持较低水平，自然增长率下降，总人口保持稳定或负增长

Age-structure pyramids/diagrams 人口金字塔

人口金字塔通过对比不同年龄的人口数量，可以推出未来的人口发展趋势和规律。

A∶增长型人口，金字塔底部人口数量最多，说明了高出生率，未来人口会不断增加

B&D∶稳定型人口，除最上部外各年龄层人口数量相似，自然增长率较低，未来人口会比较稳定

C∶衰退型人口，底部人口数量少，老龄化严重，自然增长率为负，未来人口数量可能会减少

作用∶

Predict future changes to the population growth rate of the country or region Predict the social condition of the country or region

关于人口问题的计算公式∶

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%

人口增长的影响∶

1. Food distribution: unevenly distributed 

2. Hunger: malnutrition

3. Resource use and habitat destruction

4.Infectious diseases: spread more quickly in densely populated areas 

Epidemic →limited to one area or region; pandemic → spread globally

e.g. influenza(most deadly), HIV(second-most deadly), malaria, diarrnheal diseases, tuberculosis, measles, SARS, West Nile virus