Transcript Document

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Life
Ecology: Population
Growthon
& Regulation
Earth
What is Ecology?
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From the Greek meaning “a place to live”,
it refers to the study of interrelationships
between living things and their
environment (including the nonliving
things)
The environment includes:
An abiotic component – nonliving things
such as soil, water, and weather and
A biotic component – all forms of life 
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What is an Ecosystem?
All the organisms and their environment
(nonliving) within a defined area
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What is a Community?
All the interacting populations of organisms
within an ecosystem
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How Does Population Size Change?
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A population is the members of a single
species, capable of interbreeding, that
live in a specific area
The size of the population changes
depending on the number of Births and
Deaths, the number leaving (Emigration),
and the number coming in (Immigration).
(B - D) + (I - E) = change in population size

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If life in the ecosystem is ideal, the population
will increase according to its biotic
potential, that is, its maximum rate
However, resources are limited and
organisms interact with one another for
these resources
Therefore, the population's size is limited
according to …
environmental resistance 
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The rate at which a population size changes,
I
the rate of growth, is determined by: b - d = r
(birth rate – death rate = growth rate)
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L Furthermore, the number of individuals that are
new to a population within a certain time
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period is the growth rate (r) multiplied by the
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number of members in the population at the
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beginning of the time period (N): rN =
population growth within a given time period 
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If a population is growing at an everaccelerating rate, then the population is
experiencing exponential growth
(typically a population will double during
the same unit of time for EVERY
increment of time)
Exponential growth is graphed as a J-curve
Figure 39-1 
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Life
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(i) Reproduction
begins at 4 years
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(ii) Reproduction
begins at 6 years
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What Influences Biotic Potential?
The age at which the organism first
reproduces
The frequency with which reproduction
occurs
The average # of offspring produced each
time
The length of the organism’s reproductive
life span
The death rate of individuals under ideal
conditions 
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How Is Population Growth Regulated?
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Any given area can support only a certain
population size indefinitely
This size is the carrying capacity of the
ecosystem. Population numbers that have
reached carrying capacity can be graphed
as an S-curve
Figure 39-5 
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(environmental resistance)
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carrying capacity
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equilibrium
(biotic
potential)
exponential
growth: J-curve
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time
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Population numbers are affected by the course
of nature in ways that may or may not be due
to the size of the population
Populations that get too crowded or dense may
be adversely affected by density dependent
factors such as predation, parasitism,
disease, or intense competition
On the other hand, density independent
factors, such as weather, fire events, or
human activities, impact a population
regardless of its size 
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When an animal kills and eats another
organism, predation has occurred, and
the animal doing the killing and eating is
the predator
Predation is an important mechanism in
natural population control
However, predation not only controls the
size of the prey populations, but it also
serves to control the size of the predator
populations 
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As predators reduce the number of prey
available, they are, in effect, reducing their
own food resource
This results in a reduction in the predator
population
When predator numbers are reduced, the
prey population will increase again
Thus, predator populations and prey
populations undergo population cycles 
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When an animal feeds on another organism
without killing it, the animal is a parasite,
and the organism on which it is feeding is
its host 
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When population numbers increase,
competition for the resources on which the
organisms depend becomes more intense
If the competition occurs among members of
different species, interspecific competition
is occurring
However, if the competition is among members
of the same species, the more intense
intraspecific competition is occurring 
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How Is The Human Population Changing?
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The human population grew slowly for over
one million years
During that time, fire was discovered, tools
and weapons were fashioned, shelters
were built, and clothing was made to
protect individuals
Each of these "inventions" led to a cultural
revolution as the populations adapted to
these innovations 
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The domestication of crops and animals led to
an agricultural revolution, providing a more
dependable food supply
Once advances in medicine and health care
occurred the human death rate was reduced
dramatically
This industrial-medical revolution led to an
increase in population
How is the Human Population Currently
Growing? (Figure 39-10) 
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2003
1999
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1987
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1975
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1960
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1830
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12,000 11,000 10,000
B.C.
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9000
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7000
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5000
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B.C.
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B.C.
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Technical and cultural advances
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3000
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1000
B.C.
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B.C.
Agricultural advances
B.C./A.D.
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A.D.
A.D.
Industrial and
medical
advances
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In developed countries, the industrialmedical revolution also led …
to reduced birth rates, stabilizing their
population growth
In developing countries, however, reduced
birth rates …
have not occurred, primarily due to social
traditions and a lack of access to
education and contraceptives 
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The United States is experiencing the most
rapid growth among developed countries
(Figure 39-13)
U.S. fertility rate is only 2.03, actually below
Replacement Level Fertility (RLF) which is
2.1
Continued immigration to the United States
is a significant source of this population
growth 
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U.S. population (in millions)
(1790–2003)
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year
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This migration represents a redistribution of Earth's
human population
– it may have serious implications for the environment of
both the U.S. and the Earth, because …
– Americans consume far more resources and produce
far more pollution than the global average
One measure of this effect is the "ecological footprint“
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It is more than four times greater for U.S. residents than the
global average
There is compelling evidence that, because of our
consumption of nonrenewable fossil fuels and depletion
of groundwater reserves, humans have already
exceeded the Earth's carrying capacity
Furthermore, our overgrazing of grasslands,
deforestation, etc., may actually be decreasing Earth's
carrying capacity (Figure E39-3) 
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Life
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Summary: Major Points
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This chapter has covered:
1. Factors that control the size and rate of
growth of populations
2. How the environment plays a role in
controlling populations and how individual
interactions among members of the same
species, as well as among members of
different species, influence population size
3. How a population grows may depend on how
its members are distributed within a given
area, or it may depend on the number of
offspring that survive to reach maturity
4. These factors apply to the human population
as well 
Life
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Earth