copyright © 2003 pearson education, inc. publishing as benjamin cummings unit 5: populations...

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

UNIT 5: POPULATIONS

Environmental Science


Populations

• Population- all of the organisms within a species that interact in a specific area and at a specific time– Genetic Diversity- similar

but different due to DNA

– Affected by:

• Size

• Age distribution

• Density

• Genetic composition


Principles of Ecological Factors

• Abiotic Factors- all of the nonliving parts in an ecosystem

• Biotic Factors-all of the living factors in an ecosystem

• Range of Tolerance- any variation in the physical or chemical environment that an organism can withstand before it is killed/harmed

– Law of tolerance-the existence, abundance, and distribution of a species in an ecosystem are determined by whether the levels of one or more physical or chemical factors fall within the range tolerated by that species.


Regulating Population Growth

• Limiting Factors- a distinguishing chemical or physical factor that regulates the population growth of a species; more specific than any other factor

– Limiting Factor Principle- Too much or too little of any abiotic factor can limit or prevent growth of a population, even if all other factors are at or near the optimum range of tolerance.

• Niche- an organisms functional role within an ecosystem; everything that affects the survival and reproduction

– Range of tolerance; resources it utilizes (food, space); interaction with other biota and abiotic factors; its role in the food web/matter cycle


Figure 4-13 Page 73

Terrestrial Ecosystems Aquatic Life Zones

• Sunlight

• Temperature

• Precipitation

• Wind

• Latitude

• Altitude

• Fire frequency

• Soil

• Light penetration

• Water currents

• Dissolved nutrient concentrations (especially N and P)

• Suspended solids

• Salinity

Abiotic Factors That Impact Populations


The Biotic Components of Ecosystems

Fig. 4-16 p. 75Fig. 4-16 p. 75

Producers (autotrophs)

Consumers (heterotrophs)

Decomposers


Population Ecology

• Population- how to measure?

• Growth rates: J shaped, S shaped

• K, r, and reproductive strategies

• Human population


• Population density = number of individuals in a given area or volume

• count all the individuals in a population

• estimate by sampling

How are populations measured?


• mark-recapture method depends on likelihood of recapturing the same individual

Figure 35.2A


• The dispersion pattern of a population refers to the way individuals are spaced within their area

– Clumped -

– Uniform:

– Random: no pattern


Figure 35.2C


• Idealized models describe two kinds of population growth

1. exponential growth

2. logistic growth

How do populations grow?


• A J-shaped growth curve, described by the equation G = rN, is typical of exponential growth

– G = the population growth rate

– r = the intrinsic rate of increase, or an organism's maximum capacity to reproduce

– N = the population size


Figure 35.3A

0 5 10 15 20

0

500

1000

1500

Time (years)

Pop

ula

tion s

ize

r = 0.06

r = 0.02

r = 0

r = -0.05

high intrinsicrate of increase

low intrinsicrate of increase

zero populationgrowth

negative intrinsicrate of increase


2. Logistic growth is slowed by population-limiting factors

K = Carrying capacity is the maximum population size that an environment

can support

Figure 35.3B


• logistic growth curve

– K = carrying capacity

– The term (K - N)/K accounts for the leveling off of the curve

Figure 35.3C


declining birth rate or increasing death rate

• The regulation of growth in a natural population is determined by several factors

– limited food supply

– the buildup of toxic wastes

– increased disease

– predation

Multiple factors may limit population growth


– About every 10 years, both hare and lynx populations have a rapid increase (a "boom") followed by a sharp decline (a "bust")

Figure 35.5


• Survivorship curves plot the proportion of individuals alive at each age

• Three types of survivorship curves reflect important species differences in life history

Figure 35.6


• An organism's life history is the series of events from birth through reproduction to death

• Life history traits include

– the age at which reproduction first occurs

– the frequency of reproduction

– the number of offspring

– the amount of parental care given

– the energy cost of reproduction

Evolution shapes life histories


• Principles of population ecology may be used to

– manage wildlife, fisheries, and forests for sustainable yield

– reverse the decline of threatened or endangered species

– reduce pest populations

– IPM = Integrated Pest Management


• Integrated pest management (IPM) uses a combination of biological, chemical, and cultural methods to control agricultural pests

• IPM relies on knowledge of

– the population ecology of the pest

– its associated predators and parasites

– crop growth dynamics


• In 1890, a group of Shakespeare enthusiasts released about 120 starlings in New York's Central Park

The Spread of Shakespeare's Starlings


• Today: over 100 million starlings, spread over N. Amer.

Current

1955

1945

1935 1925

1925

1935

19151905

19251935

1945

1955Current


• The starling population in North America has some features in common with the global human population

– Both are expanding and are virtually uncontrolled

– Both are harming other species


• doubled three times in the last three centuries

• about 6.1 billion and may reach 9.3 billion by the year 2050

• improved health and technology have lowered death rates

THE HUMAN POPULATION


• The history of human population growth

Figure 35.8A


Figure 35.9B

RAPID GROWTH

Kenya

Male Female

Percent of population Percent of population Percent of population

SLOW GROWTH

United States

Male Female

ZERO GROWTH/DECREASE

Italy

Male Female

Ages 45+

Ages 15–44

Under15

Under15

Ages 45+

Ages 15–44

Also reveals social conditions, status of women

• The age structure of a population is the proportion of individuals in different age-groups


• The ecological footprint represents the amount of productive land needed to support a nation’s resource needs

• The ecological capacity of the world may already be smaller than its ecological footprint


• Ecological footprint in relation to ecological capacity

Figure 35.8B

U.S.

China

India

Russia

Japan

U.S.

China

India

Russia

Japan

Per capita CO2 emissions(metric tons of carbon)

Total CO2 emissions(billion metric tons of carbon)

0 1 2 3 4 5 6 0 0.5 1 1.5

5.48

0.75

2.65

2.51

0.29

1.49

0.91

0.39

0.32

0.28


34

Part 1: Population Growth


35

Current Birth and Death Rates

• Every second: about 4 children are born, while about 2 other people die

• Net gain: 2.3 humans added to the world population every second, 72 million added every year


36

Human Population Levels Throughout History

ADD FIG. 4.2


37

ADD TABLE 4.1


38

Part 2: Limits to Growth

Varying Perspectives

• Overpopulation causes resource depletion and environmental degradation

• Human ingenuity and technology will allow us to overcome any problems - more people may be beneficial

• Resources are sufficient to meet everyone's needs - shortages are the result of greed, waste, and oppression


39

Decisions on how many children to have are influenced by many factors, including culture, religion, politics, need for old-age security, and immediate family finances.


40

Part 3: Human Demography

• Demography - vital statistics about people, such as births and deaths

• Two demographic worlds

• Less-developed counties represent 80% of the world population, but more than 90% of projected growth

• Richer countries tend to have negative growth rates


41


42

By 2050, India will probably be the world's most populous country.

(297)


43

Fertility and Birth Rates

• Fecundity - physical ability to reproduce

• Fertility - the actual production of offspring

• Crude birth rate - number of births per year per thousand people

• Total fertility rate - number of children born to an average woman during her reproductive life

• Zero population growth (ZPG) - occurs when births + immigration just equal deaths + emigration


44

Regional Declines in Total Fertility Rates


45

China's one-child-per-family policy decreased the country's fertility rate from 6 to 1.8 in twodecades. However, the policy is very controversial.


46


47

As incomes rise, so does life expectancy.


48

Living Longer: Demographic Implications

• A population growing by natural increase has more young people than does a stationary population.

• Dependency ratio - the number of nonworking individuals compared to working individuals - declining in countries such as the U.S. and Japan

• If current trends continue, by 2100 the median age in the U.S. will be 60.


49


50

Part 4: Population Growth -Opposing Factors

Pronatalist pressures

• Factors that increase people's desires to have children

Birth reduction pressures

• Factors that tend to reduce fertility


51

U.S. Birth Rates: 1910-2001


52

Part 5: Demographic Transition

• Optimistic view - world population will stabilize during this century

• Pessimistic view - poorer countries of the world are caught in a "demographic trap" - helping poor countries will only further threaten the earth's resources

• Social justice view - overpopulation due to a lack of justice, not resources


53

Demographic Transition AccompanyingEconomic and Social Development


54

Fig. 4.13


55

Infant Mortality and Women's Rights


56

Part 7: The Future of Human Populations


Figure 2.10x

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