Transcript Populations

Chapter 4: Population Ecology
Georgia Performance
Standards:
•Investigate the
relationships among
organisms,
populations,
communities,
ecosystems, and
biomes.
Essential Questions:
• EQ: How would changes in
populations affect the flow
of energy and matter in
the ecosystem?
• EQ: How are populations
regulated over time?
• EQ: How does the growing
human population
threaten the biosphere?
Chapter 4 Population Ecology
Section 1: Population Dynamics
Section 2: Human Population
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Warm-up:
• A laboratory jar containing a population of
beetle larvae (mealworms) has reached a
stable population size. We decide to add
twice as much food per day to the jar, but
this turns out to have no effect on population
size.
• What is the most likely explanation?
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Populations
• Defined by different
geographical
boundaries
appropriate to the
questions being asked
• Important characteristics:
– Density
– Geographical
Distribution
– Growth Rate
– Age Structure
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What is POPULATION DENSITY?
• The number of individuals
of a species per unit area or
volume.
• Three factors can affect
population size
– number of births
– number of deaths
– number of individuals that
enter or leave the
population
• Immigration (im-uh-grayshun), the movement of
individuals into an area,
is another factor that can
cause a population to
grow.
• Emigration (em-uh-grayshun), the movement of
individuals out of a
population, can cause a
population to decrease in
size.
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Chapter 4
Population Ecology
4.1 Population Dynamics
Population Density
 The number of organisms per unit area
Spatial Distribution
 Dispersion is the pattern of spacing of a
population.
Chapter 4
Population Ecology
Chapter 4
Population Ecology
4.1 Population Dynamics
Population Ranges
 A species might not be
able to expand its
population range because
it cannot survive the
abiotic conditions found in
the expanded region.
Common dolphin
Pupfish
EQ:
How are populations regulated
over time?
Warm-up: Population Limiting Factors
• Environmental factors that restrict population
growth.
• Some limiting factors depend on the size of the
population.
• Other limiting factors affect all populations in similar
ways, regardless of the population size.
Warm-up: Population Limiting Factors
1. Imagine a small island that has a population of five rabbits.
How might each of the following factors affect the rabbit
population?
a. climate
b. food supply
c. predation
2. Now imagine another small island that has a population of
500 rabbits. How would the same factors affect this
population?
3. Which of the factors depend on population size? Which
factors do not depend on population size?
Chapter 4
Population Ecology
4.1 Population Dynamics
Population-Limiting Factors
 There are two categories of limiting factors—
density-independent factors and densitydependent factors.
Chapter 4
Population Ecology
4.1 Population Dynamics
Density-Dependent Factors
 Any factor in the environment that depends
on the number of members in a population
per unit area is a density-dependent factor.
 Biotic factors
 Disease
 Competition
 Parasites
Population
Biology
5-2
A Section
Density-Dependent
Limiting Factor
Growth of Aphids
Exponential growth
Peak population
size
Rapid decline
Steady population
size
Steady population
size
Chapter 4
Population Ecology
4.1 Population Dynamics
Density-Independent Factors
 Any factor in the environment that does
not depend on the number of members
in a population per unit area is a densityindependent factor.
 Weather events
 Fire
 Human alterations of the landscape
 Air, land, and water pollution
Checkpoint!
1. Name 2 types of limiting factors for a population.
2. Of the following factors with the potential to limit
growth of a human population, which one is most
density-independent?
– Mass drowning caused by hurricane flood
– Freezing deaths due to a shortage of housing
Chapter 4
Population Ecology
4.1 Population Dynamics
Population Growth Rate
 The population growth rate (PGR) explains
how fast a given population grows.
 The natality of a population is the birthrate
in a given time period.
Chapter 4
Population Ecology
4.1 Population Dynamics
Exponential Growth Model
 Exponential growth
occurs when the
growth rate is
proportional to the
size of the population.
 All populations grow
exponentially until
some limiting factor slows the population’s
growth.
Chapter 4
Population Ecology
4.1 Population Dynamics
Logistic Growth Model
 The population’s
growth slows or
stops following
exponential growth,
at the population’s
carrying capacity.
Chapter 4
Population Ecology
4.1 Population Dynamics
A population stops increasing
when the number of births is less than
the number of deaths
when emigration exceeds immigration.
Chapter 4
Population Ecology
Chapter 4
Population Ecology
4.1 Population Dynamics
Carrying Capacity
 The maximum number of individuals in a
species that an environment can support for
the long term is the carrying capacity.
 Carrying capacity is limited by the energy,
water, oxygen, and nutrients available.
Concept Map
Population
Growth
can be
Logistic
growth
Exponential
growth
characterized by
No limits on
growth
Unlimited
resources
represented by
Constant
growth rate
J-shaped
curve
characterized by
Limits on
growth
which cause a
Falling
growth rate
represented by
S-shaped
curve
Checkpoint!!!
• Which of the following is NOT a condition
for a population to reach exponential
growth?
– presence of unlimited resources
– absence of predation and disease
– movement of individuals out of a population
Chapter 4
Population Ecology
4.1 Population Dynamics
 The rate strategy, or r-strategy, is an
adaptation for living in an environment where
fluctuation in biotic or abiotic factors occur.
 generally a small organism.
 Short life span
 Produces many offspring
Chapter 4
Population Ecology
4.1 Population Dynamics
 The carrying-capacity strategy, or kstrategy, is an adaptation for living in stable
environments.
 larger organism
 Long life span
 reproduce at an older age
 Produces few offspring
Chapter 4
Population Ecology
4.2 Human Population
Human Population Growth
 The study of human population size, density, distribution,
movement, and birth and death rates is demography.
Chapter 4
Population Ecology
4.2 Human Population
Technological Advances
 For 1000s of years, environmental conditions
kept the size of the human population at a
relatively constant number below the
environment’s carrying capacity.
 Humans have learned to alter the environment
in ways that appear to have changed its
carrying capacity.
Chapter 4
Population Ecology
4.2 Human Population
Human Population
Growth Rate
 Although the
human population
is still growing, the
rate of its growth
has slowed.
Chapter 4
Population Ecology
4.2 Human Population
Trends in Human Population Growth
 Population
trends can
be altered by
events such
as disease
and war.
 Human
population
growth is not the same in all countries.
Chapter 4
Population Ecology
4.2 Human Population
Zero Population Growth
 Zero population growth (ZPG) occurs when
the birthrate equals the death rate.
 #s at pre-reproductive, reproductive, and
post-reproductive ages being approximately
equal.
Chapter 4
Population Ecology
4.2 Human Population
Age Structure
 A population’s
age structure
is the number
of males and
females in
each of three
age groups:
pre-reproductive stage, reproductive stage, and postreproductive stage.
Chapter 4
Population Ecology
4.2 Human Population
Human Carrying Capacity
 Scientists are
concerned about the
human population
reaching or exceeding
the carrying capacity.
 An important factor is the
amount of resources from
the biosphere that are
used by each person.
Pop Quiz
1. Name 2 types of limiting factors for a population.
2. Of the following factors with the potential to limit
growth of a human population, which one is most
density-independent?
– Mass drowning caused by hurricane flood
– Due to overcrowding in Asian villages, many children did
not survive
Pop Quiz
3. Which of the following is NOT a
condition for a population to reach
exponential growth?
– presence of unlimited resources
– absence of predation and disease
– movement of individuals out of a population
Classwork:
• Complete chapter 4 study guide in class.