Transcript Populations

Part 2
Populations & Communities
Bell Work
You have just been hired for a summer job for the month of July.
You have two options on how you would be paid. You can be
paid $50/hour (Option A). Or (Option B) you can be paid one
cent on the first day of the month. Each day following, your pay
will be double what it was the previous day. Take a few minutes –
no calculators! – to write down some estimates as to how much
money you would earn on the tenth, twentieth, and final day of
July. Which option would you choose?
Where We Came From…
Where We’re Going.
• You learned about ecosystems in Part 1.
• What are some themes from that section?
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–
–
–
Biodiversity
Succession
What defines an ecosystem
What are the major terrestrial biomes and what distinguishes
them from on another.
• Life is interconnected: this is one that you should
remember.
• We are going to take this and couple that with another
theme of biology… how populations are quantified and
what influences them.
• Sustainable growth can only happen as long as there is
balance with everything else we share this Earth with.
• This is a fact of life that the human population is going to
have to come to terms with.
Objectives Populations
• Explain the importance of studying
populations.
• Compare exponential growth with logistical
growth.
• Identify factors that affect population sizes.
• Explain how science and technology have
affected human population growth.
Vocabulary
• Population
• Carrying capacity
Studying populations: A Case Study.
• In the 1850’s, a man introduced two dozen (24) rabbits were to
his new home in Australia, “to remind him of home”.
• There was an abundance of food and no predators.
• Sounds great for the rabbits!
• By the 1950’s there were over 6 million rabbits!
• Do you think that the rabbit population had an affect on their
new ecosystem?
• What do you think was affected by this new organism?
• Think about these for a minute.
What Is a Population?
• Studying populations and understanding population growth is
important because populations of different species interact and
affect one another, including human populations.
• A population is made up of a group of organisms of the same
species that live together in one place at one time and interbreed.
– Populations can be small or large.
– Some populations stay stable at nearly the same number for years.
– Some populations change from lack of resources, disease, man-made
influences, migrations, natural disasters, or predation.
– Other populations can grow rapidly, uncontrolled.
• Remember, life is almost always interconnected…
sometimes much more than is understood.
• This means that nearly every population in an ecosystem
affects the other around it.
Population Growth…How Populations Grow?
• Whether a population grows or shrinks depends on obvious
things like births & deaths, but organisms can enter or leave
populations too.
The four major ways organisms enter or leave populations:
 (1) Births +…
• (2) Immigration is the movement of individuals into a
population.
• & (3) Death +
• (4) Emigration is the movement of individuals out of a
population.
• Growth = (births + immigration) – (deaths + emigration)
• These are terms for all organisms.
• The result is that populations can grow (+Growth) or shrink (Growth).
I
Emigration
ration
Emigration
Emigration
Im
Emigration
Two Population Growth Models
• To study populations completely you need to understand the
population models and be able to interpret them.
• A simple population model describes the rate of population
growth as the difference between birthrate, death rate,
immigration, and emigration as a function of time.
J-shaped
S-shaped
Population Growth, continued
• Exponential growth occurs when
numbers increase by a certain factor
in each successive time period.
• For example:
– X2 (time) = Y (# of individuals)
• This type of increase gives the
J-shaped curve of exponential
growth.
• In exponential growth, population
size grows slowly when it is small. But
as the population gets larger, growth
speeds up dramatically.
Exponential Growth…Revisit the bell work.
•
•
•
•
•
If you start with 1 penny and double it every day after that.
How many pennies would you have after 5 days?
How many after 10 days?
How many after 15 days?
How many after 20 days?/25?/30?
1
2
4
8
16
32
64
128
256
512
1024
2048
4096
8192
16384
32768
65536
131072
262144
524288
Day 25 = $167,772.16
Day 30 = $5,368,709.12
• What would graph of time versus pennies look like? vs. $37, 200 @ $50/hr
What would graph of time versus pennies look like?
1 2 3 4 5 6 7 8 9 10
Number of Pennies (thousands)
Doubling every day.
Hourly
5
10
15
Days
20
Population Growth
• Logistic growth is population
growth that starts with a
minimum number of individuals
and reaches a maximum
depending on the carrying
capacity of the habitat.
There are three growth rates in
logistical growth.
1. Initial slow growth
2. A stage of exponential growth
3. Stabilization around the carrying
capacity.
Take note of the shape. What does
it look like?
What’s Limits
Population Growth?
• Eventually, (even with exponential growth)
population growth usually slows and may
stabilize or even crash.
• This is because an ecosystem can support
only so many organisms due to limited
resources such as water and food.
• Whatever the case, the largest population
that an environment can sustain (support
for long periods of time) at any given time
is called the carrying capacity.
• When the carrying capacity of an
ecosystem is reached, one characteristic
exists…
• death rate (& other negatives) equals the
birthrate (& other positives)
• Natural populations usually fluctuate as they
stabilize around the carrying capacity of the
environment and reach a balance between
the organisms and the resources in the area.
Two Population Growth Models
J-shaped
S-shaped
Concept Check
Choose the best
answer for these 4
questions.
1. Which time period shows the largest growth of the population?
a. A
c. C
b. B
d. D
2. During which time period are the birth rate and death rate equal?
a. A
c. C
b. B
d. D
3. During which time period does the growth of the population equal
zero?
a. A
c. C
b. B
d. D
4. During which time period does the population decrease?
a. A
c. C
b. B
d. D
Population Growth
• Things to consider:
• Growth causes organisms to come into contact more
often.
• Competition for food, shelter, and mates increases
between individuals of a population as it grows.
• Furthermore, the more of a certain type of prey will
mean more food to support predators.
• This infers that predator and prey populations are
interdependent.
• These causes affect the rate of growth and cause it to
slow until stability is reached.
Factors That Affect Population Size
• Most populations increase or decrease a little.
– Some change with the seasons.
– Others have good years and bad years.
• A combination of 4 factors cause populations to
grow and shrink.
• They include;
– Biotic Factors: Living things
– Abiotic Factors: Non-living things
– Density-Dependent Factors: How close an organism
is to another.
– Density-Independent Factors: Cause changes
regardless of proximity
Population Growth
• You learned that biotic and abiotic factors shape ecosystems and
influence population growth.
• Population growth is also controlled by two density-related
factors:
– Density refers to the number of organisms in a specific habitat
• Density-dependent factors are variables affected by the number
of organisms present in a given area.
– Examples include:
• nesting sites,
• amount of food/water.
• Density-independent factors are variables that affect a population
regardless of the population density.
– Examples of density-independent factors are
• weather,
• floods, and
• fires.
– These will happen regardless of how many organisms are alive there…these
are the wild-cards of population growth.
• What factor do you think disease is?
Factors Affecting Population
ABIOTIC FACTORS
Weather
Climate
Natural Disaster
DENSITY DEPENDENT
Non-living
How many individuals live in the area.
Nesting Sites
Water
Camouflage
Natural Disaster
Living
DENSITY INDEPENDENT
Food
Mates
Number of Offspring
Predation
BIOTIC FACTORS
Human Impacts That
Affect Populations
• There are always other factors…
• Humans affect populations of
many species as well.
• Most of the time, humans
cause populations to drop by
disrupting or destroying
habitats, introducing diseases,
or introducing nonnative
species (invasive species).
Human Population
• For most of human history, there
have been fewer than 10 million
people on the entire planet.
• Two thousand years ago, there
were only 300 million people.
• Around the time of the Industrial
Revolution, (the late 1700s) the
human population started to
accelerate rapidly, exponentially.
• Now, there are close to 7 billion
people, and some scientists think
that the population will grow to 9
billion in 50 years.
• What biotic & abiotic factors are going to be a significant
problem?
Human Population Growth. What type of growth is this indicative of?
Exponential Growth
Linear Growth
Human Population: Causes/Affects
• Humans are subject to the same factors that limit other
organisms growth but things are obviously different for
humans.
• What has affects on our growth curve?
• Science and technology are major reasons why the human
population is growing so rapidly.
• Advances in agricultural technology have allowed efficient
(but controversial) production of crops, livestock, and other
foods. More food supports more people but also contributes
to environmental sacrifices.
• Medical advances have also allowed the human population to
increase. Vaccines and antibiotics have lowered the death
rate. Other medical advances have allowed adults to live
longer lives.
• Better sanitation and hygiene, disease control, and
agricultural technology are a few ways that science and
technology have decreased the death rate of the human
population.
Human Population, What We Need to
Watch Out For…
• As more humans live on the planet, more resources
will be needed to support us.
• As demand for resources increases, more pressure
will be put on Earth’s ecosystems to provide them.
– For those interested, a study into food production in the
US is extremely interesting and informative…somewhat
frightening.
– See Food Inc.
• Will there be problems in the future for humans?
• Science already believes there will be.
An Interesting Comparison
• The human growth rate is unique in nature because
we haven’t found our ecosystem’s carrying capacity
yet.
• WE ARE UNIQUE IN NATURE!!!
– We keep increasing and increasing in numbers with no sign
of slowing.
– What is our ecosystem?
– What are abiotic factors that influence our growth?
• Global warming? Loss of land? Pollution/trash?
– What are the biotic factors that could have an influence?
• Lack of food or contaminated food? Disease?
– Is disease density-dependent or density dependent?
Population Pyramids
• Population pyramids break down populations by age and
sex to see exactly how these pieces of data compare to
other countries.
• They can indicate whether or not a population is growing,
shrinking or stabilized.
•
Factors to consider:
• Everyone will die
but how many
live to see old
age?
• The middle-aged
people are the
one who have
children.
• Children will soon
grow to
reproductive age,
contributing to
the population.
•
Population of a Stable Country
Population Pyramids
• Which country is stable?
• Which country is facing rapid growth?
Indication
of life spans
Babies eventually
grow to have babies.
Classwork/Home Work
• Human Populations Growth Graphing Analysis
– Lab (50pts)
– In groups of 2 (put both names on it!)
– One packet per group of two.
• (note that the instructions incorrectly tell you the
values for the x-axis is 0 A.D. to 2020 A.D.. This should
be 0 – 2100 A.D.. & the y-axis should be 0 – 8.25 billion,
not 0 – 20 million. Sorry. These instructions were for a
different set of data)
• “Population Growth” WS is homework.
Interpreting Graphs
Answer the following questions on a separate sheet of paper.
Use the graph below to answer questions 1–3.
Read each question, and write your answer in the space provided.
1. What type of population growth pattern is shown in the graph above?
2. Describe the growth of the hypothetical population shown in the graph, beginning with just a few
breeding pairs.
3. What is the probable eventual fate of the hypothetical population represented in the graph?
Use the graph below to answer questions 4–7.
Read each question, and write your answer in the space provided.
4. Between what years does this graph predict that the human population growth rate will start
slowing?
5. According to this graph, what will the world human population be in 2050?
6. From 1750 to 2000, which type of population growth model does this graph more closely
represent?
7. If you could continue the graph to the year 3050, predict the type of population growth model this
graph would represent. Explain your answer.
1. Exponential growth
2. In the beginning, there are just
a few breeding pairs. Growth
was slow and linear in the
beginning. At a certain point,
the population reached a point
of exponential growth.
3. Eventually, population will
stabilize around its carrying
capacity.
4. Roughly 2025.
5. Close to 9 billion.
6. Exponential growth.
7. Predicted out to 3050, based
upon the prediction that the
growth rate starts to slow, the
model will start to look more
like the logistical growth model
and the population may
stabilize around 9 million.
Plotting Data: Population Quick Lab
You can learn a lot about the concept of population growth by
plotting data on a graph and studying its changes. In this activity
you will plot the growth of a deer population.
Methods:
1.On the paper I provided you, plot the data from the table.
2.Title the graph and label the x & y axes.
3.Answer the questions.
Questions: Answer to the best of your ability as groups of two.
Each person must help and contribute but you may work with
the others at your table. We will go over the answers together,
Monday.
Graph 1. Title:
ID IV & DV.
Know the minimum and
maximum values for both
the independent and
dependent variables.
- Luckily, this graph is easy
as time is almost always
the independent variable
(the x-axis).
Set the values for each
interval the same so that all
information fits in the axis.
- This prevents
misinformation from
being presented in the
graph.
- Remember, a graph is
only as useful as it is set
up. We use graphs to
easily identify trends and
correlation.
Human Population Growth.
How do you set up your graph so it’s correct?
240
200
160
120
80
40
0
Population of Deer
260
280
Population growth HW
1930
’40
’50
’60
’70
Year
’80
‘90
Factors Affecting Population
ABIOTIC FACTORS
Weather
Climate
Natural Disaster
DENSITY DEPENDENT
Non-living
How many individuals live in the area.
Nesting Sites
Water
Camouflage
Natural Disaster
Living
DENSITY INDEPENDENT
Food
Mates
Number of Offspring
Predation
BIOTIC FACTORS
Population Pyramids Human Population
• Draw and label
Old Age
Young age