Download Unit 5

Environmental Science
UNIT 5: POPULATIONS
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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
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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.
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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
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Abiotic Factors That Impact Populations
Aquatic Life Zones
Terrestrial Ecosystems
• Sunlight
• Temperature
• Precipitation
• Wind
• Latitude
• Altitude
• Fire frequency
Copyright
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• Soil
Light penetration
• Water currents
• Dissolved nutrient
concentrations
(especially N and P)
• Suspended solids
Figure 4-13 Page
• Salinity
•
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The Biotic Components of Ecosystems
Producers (autotrophs)
Consumers (heterotrophs)
Decomposers
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Fig. 4-16 p. 75
Population Ecology
• Population- how to measure?
• Growth rates: J shaped, S shaped
• K, r, and reproductive strategies
• Human population
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How are populations measured?
• Population density = number of individuals in
a given area or volume
• count all the individuals in a population
• estimate by sampling
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• mark-recapture method depends on likelihood
of recapturing the same individual
Figure 35.2A
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• The dispersion pattern of a population refers
to the way individuals are spaced within
their area
– Clumped – Uniform:
– Random: no pattern
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Figure 35.2C
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How do populations grow?
• Idealized models describe two kinds of
population growth
1. exponential growth
2. logistic growth
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• 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
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Figure 35.3A
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high intrinsic
rate of increase
1500
Population size
1000
low intrinsic
rate of increase
500
r=0
zero population
growth
negative intrinsic
rate of increase
r = -0.05
0
0
5
10
Time (years)
15
20
2. Logistic growth is slowed by populationlimiting factors
K = Carrying capacity is
the maximum
population size
that an environment
can support
Figure 35.3B
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• logistic growth curve
– K = carrying capacity
– The term
(K - N)/K
accounts
for the
leveling
off of the
curve
Figure 35.3C
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Multiple factors may limit population growth
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
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– 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
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• 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
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Evolution shapes life histories
• 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
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• 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
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• 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
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The Spread of Shakespeare's Starlings
• In 1890, a group of Shakespeare enthusiasts
released about 120 starlings in New York's
Central Park
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• Today: over 100 million starlings, spread over
N. Amer.
Current
1955
Current
1955
1945
1935
1925
1945
1905
1915
1935
1925
1925
1935
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• 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
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THE HUMAN POPULATION
• 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
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• The history of human population growth
Figure 35.8A
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• The age structure of a population is the proportion
of individuals in different age-groups
RAPID GROWTH
SLOW GROWTH
ZERO GROWTH/DECREASE
Kenya
United States
Italy
Male
Female
Male
Female
Ages 45+
Ages 45+
Ages 15–44
Ages 15–44
Under
15
Percent of population
Male
Female
Under
15
Percent of population
Percent of population
Also reveals social conditions, status of women
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Figure 35.9B
• 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
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• Ecological footprint in relation to ecological
capacity
Figure 35.8B
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Per capita CO2 emissions
(metric tons of carbon)
0
1
2
3
U.S.
China
5
6
5.48
2.65
Japan
2.51
0.29
0
0.5
1
U.S.
Russia
Japan
India
1.5
1.49
China
0.75
Russia
India
4
Total CO2 emissions
(billion metric tons of carbon)
0.91
0.39
0.32
0.28
Part 1: Population Growth
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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
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Human Population Levels Throughout History
ADD FIG. 4.2
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ADD TABLE 4.1
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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
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oppression
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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.
39
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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
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(297)
By 2050,
India will
probably
be the
world's
most
populous
country.
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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
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+ emigration
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Regional Declines in Total Fertility Rates
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China's one-childper-family policy
decreased the
country's fertility rate
from 6 to 1.8 in two
decades. However,
the policy is very
controversial.
45
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As incomes rise,
so does life
expectancy.
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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.
48
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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
50
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U.S. Birth Rates: 1910-2001
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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
52
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Demographic Transition Accompanying
Economic and Social Development
53
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Fig. 4.13
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Infant Mortality and Women's Rights
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Part 7: The Future of Human Populations
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Figure 2.10x
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