Download Communities and Populations

Communities and Populations
Succession (Revisited)
• As an ecosystem changes, older inhabitants
gradually die out and new organisms move in,
causing further changes in the community =
ecological succession
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–
–
–
Primary succession = occurs on bare rock
Pioneer species = first species to populate an area (lichens)
Secondary succession = a disturbance changes an existing community
Climax community = mature, stable community after specific,
predictable stages of succession
• Biotic factors develop on abiotic factors
Succession
Do Now
• What may cause the size of a population to
grow?
• What may cause the size of a population to
decrease?
How populations grow?
• Since organisms are constantly interacting,
growth or decline of one population will effect
another population!
• Remember: Relationships in food chains show
effects of population growth or decline.
Characteristics of Populations
• Important characteristics of a population:
– Geographic distribution = “range” of area
inhabited by a population
– Density = number of individuals per unit area
– Growth rate = change in the number of individuals
over time
Population Growth
• Populations may stay the same size from year to
year, or may grow/decline rapidly due to the
removal/introduction of a predator or the
introduction/removal of prey.
• Population size is effected by:
– Number of births
– Number of deaths
– Number of individuals that enter or leave the
population
• Immigration = movement of individuals into area (growth)
• Emigration = movement of individuals out of population
(decline)
Exponential Growth
• If a population has abundant space and
food, and is protected from predators
and disease, then organisms in that
population will multiply and the
population size will increase.
• Exponential growth occurs when the
individuals in a population reproduce at
a constant rate
– Think of asexually reproduction:
population doubles over and over again
approaching an infinitely large size
– Results in “J”-shaped curve
• Under ideal conditions with unlimited
resources, a population will grow
exponentially.
Logistic Growth
• Exponential growth does not continue
in natural populations for very long.
• As resources become less available, the
growth of a population slows or stops.
• Logistic growth occurs when a
population’s growth slows or stops
following a period of exponential
growth
– Results in “S” shaped curve
– The largest number of individuals that a
given community can support = carrying
capacity
Quick Activity
• Analyze data
Interest Grabber continued
Section 5-2
Do Now
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?
Go to
Section:
Limits to growth
• An environmental interaction can change the growth
rate of a population by changing the relationship
between birthrate and death rate, or between rates
of immigration and emigration.
• A limiting factor = a factor that causes population
growth to decrease
• Some limiting factors include:
–
–
–
–
–
Competition
stronger effect as
Predation
population grows
Parasitism and disease
regardless of
Drought and other climate extremes
population size
Human disturbances
Figure 5-7 Wolf and Moose
Populations on Isle Royale
Section 5-2
60
2400
50
2000
40
1600
30
1200
20
800
10
400
0
1955 1960
0
1965
1970
1975
Moose
Go to
Section:
1980
Wolves
1985
1990
1995
Density-Dependent Factors
• A limiting factor that depends on population size including:
– Competition – organisms struggle for resources
• When organisms of different species compete, it forces evolutionary
change to decrease competition (evolve to occupy separate niches)
– Predation – predator-prey relationship controls population
– Parasitism – control population by weakening/killing host
– Disease - control population by weakening/killing host
• Density dependent factors become limiting only when the
population density (number of organisms per unit area)
reaches a certain level
• These factors operate most strongly when a population is
large and dense
Density-Independent Factors
• Affect all populations in similar ways, regardless of the
population size including:
–
–
–
–
Unusual weather
Natural disasters
Seasonal cycles
Human activities (damming rivers/clearing forests)
• Many species will show a characteristic “crash,” then the
population will build back up right away, or stay low for some
time
• Environments are always changing, and most populations can
adapt to a certain amount of change by growing or shrinking
in size.
• Major upsets in the ecosystem can lead to long-term declines
in certain populations (human activities)
Quick Activity
• Gray Wolf Population Reading
Human Population Growth
• Like other populations, the size of the human
population tends to increase with time.
– Long ago, the human population was limited by
food, disease, and survival to adulthood rates
were low
– About 500 years ago, the human population
began growing rapidly with agriculture and
industry making resources readily available,
improved sanitation, medicine and health care.
Human Population Growth
Section 5-3
Industrial
Revolution
begins
Agriculture
begins
Plowing
and
irrigation
Go to
Section:
Bubonic
plague
Patterns of Population Growth
• The human population cannot grow exponentially
forever, because resources are limited.
• In 1800s, Malthus predicted war, famine and disease
would limit human population growth
• Today, scientists study human population including
birthrates, death rates, and age structure to predict
growth rates = demography
Demographic Transition
• Demographers have developed a hypothesis to explain a
slowing of population growth using changing in birth and
death rates = demographic transition
– Initially, birthrate and death rate are equally high
– Then, advances decrease death rate, while birth rate remains high
(more births than deaths and population increases)
– Then, modernization decreases birthrate, and population growth
slows
– Eventually, birthrate and death rates are equally low and population
growth stops
Age Structure
• Population growth also depends on how many
people of different ages make up a given
population
• Demographers can predict future growth
using models that graph the numbers of
people in different age groups in a population
= age-structure diagrams or population
profiles
Figure 5-13 Age Distribution
Section 5-3
U.S. Population
Males
Go to
Section:
Females
Rwandan Population
Males
Females
Future Population Growth
• Demographers can predict worldwide human population
growth in future by analyzing age structures of every country
– By 2025, 7.8 billion
– By 2050, 9 billion
– However, by 2050, the growth rate may begin to slow in a
demographic transition
• Many ecologists suggest that if human population growth
doesn’t slow down, there could be serious and lasting damage
to the environment and global economy
• Other scientists believe that science, technology, and positive
changes in society will help control negative impacts of
humans
Quick Activity
• Analyze human population growth