Transcript Populations

Populations
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Population- the number of individuals of a species tha
inhabit a particular area at the same time.
2 characteristics of populations
1. Population Density
2. Population dispersal
Population Density
• The number of individuals of a population
that inhabit a certain area (land or water)
• Example) there is a population of 10 million
people in los angeles
• Give 3 examples of population density
Population Dispersal
• How individuals in a population are
dispersed or spread out in an area.
3 ways populations can be
dispersed
1. Random- location of organisms is random
and not dependent on other
members of the species
Ex) dandelion seeds being randomly spread in
a field
VERY RARE
2. Clumping – Individuals of a population clump
or flock together ** most common kind**
Ex) fish swim in schools or groups
In this kind of dispersion animals “clump” near resources
3. Uniform- members of population are
uniformly spread out in region or area
• results from competition for resources,
members of a population need to spread out
because of limited resources
• Farmers create artificial uniform distribution
Factors Controlling Distributions
Summer
In eastern Connecticut,
The Black-capped
Chickadee’s moves its
geographic range south
in winter (summer left,
winter right; darker
colors are denser
populations) because its
physiological need for a
warmer climate is
better met there.
Winter
You do!
• What are two important characteristics of
populations- explain each
• Name and describe three kinds of
population dispersion & explain them
• Population density and dispersal
• Random, uniform, clumping
Population Growth
Questions we need to be able to answer
• How do populations grow?
• What determines if populations grow or
not?
• What patterns are there for population
growth?
2 Factors that regulate population
growth
• Density-dependent factors- certain factors limit
growth. These include disease and availability
of food and living space. As populations
increase, mortality increases
• Density-independent factors- other factors
influence populations regardless of their size.
These include storms, forest fires, geologic
events, minimum winter temperatures and
snowfall amounts.
Two main kinds of populations:
r and K Strategists/organisms
r-selected/ r-strategist
K-selected/k-strategist
Reproduce early in life
High reproductive growth
Don’t care for young
(bacteria, amoebas)
Reproduce late in life
Have few young
Devote much time and
energy to survival of
young
Humans, tigers, dogs
Words and concepts we need to
know:
• Biotic Potential-The amount that a population
would grow if there were unlimited resources in
the environment
• Are there unlimited resources in an
environment? What keeps populations from
reaching their biotic potential?
• Resources ARE limited in ecosystems so
populations DO NOT reach their biotic
potential.
• Organisms reach “carrying capacity”
Carrying Capacity (K)
» The maximum population size that can
be supported by the available
resources in an area.
» Different ecosystems have different
Carrying capacities for different
species because all species have
different requirements for life!
You do
• In a forest what populations would have a high carrying
capacity? Why
• What is the difference between biotic potential and
carrying capacity?
• Give an example of an r-strategist
• Give an example of a K-strategist
• What species would have a lower carrying capacity- why?
4 stages of population growth
• 1. Lag phase- population grows slowly
• 2.Exponential Phase- population grows
rapidly/ exponentially (growth exceeds
death rate)
• 3.Stationary Phase – Population stops
growing and stays relatively stable. (equal
numbers of birth and death)
• 4.Death phase- more members are dying
than being born or moving in (immigration)
so the population is decreasing
Showing carrying capacity
RULE OF 70
• The rule of 70 tells us how long it will take a
population to double in size
• Formula - 70 divided by the current growth rate
• Example) The growth rate of a population is 5%
per year. How long will it take for the population
to double
• 70/5= The population will double in.
Everyone Practice!
• US population =311 million, growth rate is 0.883
How long will it take US to double?
• World population is 7 billion growth rate is 1.2
How long till we double?
• What happens then?
Patterns of Population Growth
1. Logistic Population Growth- population grows
fast at first then becomes stable and remains at
carrying capacity- S shaped curve
Population Growth
Population Size
70
60
---------------------------------------------------------------------------------- K
50
40
30
20
10
0
0
5
10
Day
15
Population cycles in ecosystems
In nature populations generally follow one of
two patterns
Boom and Bust cycle
Common among r-strategists
rapid decrease- cyclical
Rapid increase followed by
Predator prey cycle
Predator Prey Cycle
• Populations of predator and prey influence
each other
• Prey population grows rapidly
• Predator population grows after prey is
established
• Prey begin to die out
• Predators die out
• Cycle continues.
Your turn:
• Find the doubling rate for a population that
has a growth rate of 1.5
• What two cycles of population growth exist
in nature
• Name the 4 stages of population growth and
give an example of each
Human Population Dynamics
How do populations change
• Immigration – movement of people or species into
a population
• Emmigration – movement of people or other
species out of a population
** In general these are not significant factors in
population size& DO NOT affect global
population ***
Fertility Rates
• Replacement level fertility (RLF)
– Number of children a couple must have to replace
themselves
– 2.1 in developed countries (DCs) 2.5 in some lessdeveloped ones (LDCs)
– Have to take infant mortality into account
• Total Fertility Rate
The number of children a woman will bear
during her lifetime.
• Total Fertility Rate is decreasing globally
however world population is still increasing.
*** TFR = most significant addition to human
population******
Projected Birth Rates by
Region
World Population Growth Rate
Goal
• Total fertility rate = replacement rate
• Still does not equal zero population growth
because of people living longer
Factors that affect the growth rate of
Human Populations
Anything that impacts TFR (total fertlility rate)
impacts population growth.
Examples>
Availability of birth control
Demand for children in the labor force
Urbanization (rural communities have children for
labor)
Base level of education for women
Religious beliefs, customs and traditions
You do
• Identify and describe two factors that affect
TFR
• Explain the difference between TFR and
RLF
Factors not related to TFR that affect
population
DEATH RATE ALSO AFFECTS
population!!!!
The reason the worlds population has grown
in the past 100 yrs is due more to later death
rate than higher birth rate
Why are people living longer?
• Industrial Revolution improved standard of
living
• Clean water
• Better sanitation (fewer diseases)
• Dependable food supply
• Better health care
2 generalization about population
• The more industrialized or developed the nation
the longer the life span
• Overall health of a population can be estimated by
looking at lifespan AND mortality rate of infants.
Life span: Afghanistan = 44yrs. Japan = 80yrs
Infant Mortality: Afghanistan=121/1000
US= 6/1000
Age Structure pyramids
Exit ticket
• Name three factors that affect TFR
• What are two generalizations you can make
about populations?
• What can age structured pyramids tell yougive at least two things.
Age Structured worksheet here!
Demographic Transitions!
Demographic Transition Model
Used to predict population trends based on birth and death rates
of a population.
• Environmental Resistance- anything that
slows a population’s growth – such as
harsh living conditions, lack of clean
water, lack of medical care etc.
Zero population growth occurs when
either:
a. High birth rates and high death rates
b. Low birth rates and low death rates.
Demographic Transition - When a population
moves from situation a- to situation b
There are 4 stages that occur before
a demographic transition happens!!
1.
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Pre Industrial StateSlow growth
High birth rate
High death rate
Harsh living conditions
2. Transitional State• RAPID population growth
• High birth rates
• Lower death rates due to food, clean water,
and improved health care
3. Industrial State:
• SLOW population growth
• Birth rate drops
• Birth rate and death rate are close but not
equal
• *** Developing countries are in this state**
4. Post Industrial State
• Population approaches or reaches zero
population growth!!!!
• Populations can drop below zero population
growth (negative growth) (russia)
You Do
• Describe in your own words the stages of
the demographic transition model
• What stage has high birth and low death?
WHY
• Why do countries tend towards zero
population growth when industrialization
occurs? Identify and describe 2 reasons.
Endangered/extinction
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One reason so many big cats are endangered
Habitat destroyed
Prey dies
Predator has no food
Species without food go extinct