Ecology Unit
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Part A What is ecology?
Everything that surrounds a living thing makes up its environment. Living things are
affected by their environments. Living things also have an effect on their environments.
The study of livings things and their environments is called ecology. Scientists who study
ecology are called ecologists. Ecologists study the relationships between living things
and their environments. They also study haw living things are adapted, or suited, to
their environments.
All living things need materials to carry out their life processes. Organisms get all
the materials they need from their environments. Some materials, called nutrients, are
used by living things for growth and energy. Green plants get nutrients and water from
the soil. They take carbon dioxide from the air. They use sunlight and carbon dioxide to
grow and make food for energy. Plants also need oxygen. Some animals get nutrients
and energy from eating plants. Some animals eat other animals. Most animals get
oxygen form the air. Fish get oxygen that is dissolved in the water.
Look at the picture above. It shows an area that may be found on the edge of a
field or wood. There are many different kinds of organisms that live in this type of
environment. The organisms in this environment interact, or act upon each other. The
organisms also interact with the non-living parts of the environment. The rabbit eats
grass that is growing in the soil. The wastes produced by the rabbit enrich the soil. The
enriched soil makes the grasses grow better. The grasses, soil, and rabbit each have an
effect on each other. An interaction also takes place between the fox and the rabbit.
The fox eats rabbits. If there are many foxes hunting the rabbits, the number of rabbits
will go down. With fewer rabbits, some of the foxes will die from lack of food. As a
result, the number of foxes will go down.
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Name:_________________________
Date:__________________________
Part A What is Ecology Review
1. What will happen to the number of rabbits if the fox population goes
down?
2. What is the study of living things and their environments called?
3. What is the name given to materials that living things use for growth
and energy?
4. What is the name of the specialist that studies the relationships
between living things and their environments?
5. What need would a green plant not be able to get growing in a dark
cellar?
Fill in the following blanks with the word or words that best completes the
sentences.
6. Plants use ______________________________and sunlight to grow and
make food.
7. All the organisms in an environment ______________________________
with each other.
Part B What is an ecosystem?
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A population is all of the same kind of organism living in a certain place at
a certain time. An example of a population is the number of worms that live in a
square meter of the soccer field today.
Different populations may live in the same
environment. Look at the picture of the rotting
log to the left. There are some mushrooms
growing on the log. These 5 mushrooms make
up one population of the log. Count the
number of mice living in the log. The mouse population of the rotting log at the
time of the drawing was 4.
All the populations living on the rotting log make up a community. A
community is all the populations that live in a certain place at the same time. It
includes all the different kinds of living things that live together. The rotting log
community seen above contains mushrooms, ferns, mice and probably some
bacteria.
The organisms in a community interact with the nonliving parts of the
environment. The organisms in the community also interact with each other. The
living and non-living things in an environment, together with their interactions,
make up an ecosystem.
There are many kinds of ecosystems. They are different sizes and have
different organisms in them. An ecosystem can be as large as a desert or as
small as a rotting log. Ecosystems can be rives, lakes or ponds. Even a puddle of
water can be an ecosystem.
An ecosystem is a self-supporting unit. Four processes occur in an
ecosystem to make it self supporting.
1. Production of energy - The sun is the source of energy in most
ecosystems.
2. Transfer of energy – Energy is transferred from the sun to plants that
make their won food. The stored energy in plants is transferred to other
animals that eat the plants. Energy is transferred to other animals when
they eat the plant-eating animals.
3. Breaking down materials – When organisms die, their bodies
decompose, or breakdown. The chemicals are reused by other living
things.
4. Recycling – The materials needed by organisms in an ecosystem are
recycled or used over and over.
All the ecosystems of the earth are connected in some way. All the
ecosystems of the earth make up the biosphere. The biosphere is made of the
area of the atmosphere (air), lithosphere (land) and the hydrosphere (water)
that has life in it.
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Name:________________________
Date:_________________________
Part B What Is an Ecosystem Review
1. Look at the rotting log picture on page 3. What is the fern population in the log
community?
Fill in the blanks with the word or words that best complete the sentence.
2. All the different kinds of organisms that live in a pond make up a
_____________________________________.
3. All the living and nonliving things tin an environment together with their
interactions make up a(n) ______________________________________________.
4. In most ecosystems, the major source of energy is the
__________________________________________.
5. When organisms die, their bodies __________________________________________.
6. When animals eat green plants, the stored __________________________________ in
the plants is transferred.
Use the picture to the right to answer the following questions.
7. What is the turtle population of
the pond ecosystem?
8. Name 3 different populations
living in or around the pond
ecosystem. (No you can’t use
the turtles as one)
a.
b.
c.
9. Using information from Part B reading, explain why the pond in the picture is an
ecosystem.
Part C Roles in a community
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The role an organism plays in a community is its niche. Just like you
play a certain role in your family community, organisms play a certain role
in their eco-community. These roles are very important to the ecosystem.
An organism’s niche in a community is often defined by the way it gets its
food or what it eats.
Organisms that make their own food are called producers or
autotrophs. Producers use energy from the sun to make food. On the land,
the main producers are plants. The main producers in lakes and oceans
are algae. The autotrophs are very important to an ecosystem. They take
the sun’s energy and change it into chemical energy that the other
members of the ecosystem can use.
Most organisms get food by eating other organisms. An organism
that eats other organisms is a consumer. Rabbits eat grass and other plants.
Rabbits are primary consumers. A primary consumer is an organism that
eats producers. Sometimes they are called herbivores. Consumers that
eat primary consumers are secondary consumers. (DUH!) Weasels eat
small plant-eating animals, such as rabbits. Weasels are secondary
consumers. Consumers that eat secondary consumers are tertiary
consumers or third order consumers. Hawks eat small meat-eating animals,
such as weasels. Hawks are tertiary consumers. Some animals, such as
hawks, ar both secondary and tertiary consumers. Animals that only eat
other animals are called carnivores. People can be primary consumers,
secondary consumers or tertiary consumers. People are not considered
herbivores or carnivores. They are omnivores. They eat both plants and
animals.
Some animals feed upon dead
animals. These animals are
scavengers. Scavengers eat animals
that have died or been killed by other
animals. Vultures, hyenas, and certain
ants, beetles, and worms are
scavengers. Scavengers are both
secondary and tertiary consumers.
Organisms that break down wastes or
remains of organisms are decomposers. Decay bacteria are
decomposers. All fungi are decomposers. The scavengers and
decomposers are important to the ecosystem because they recycle
materials back into the ecosystem.
Name____________________
Date:_____________________
Part C Roles in a community Review
Define the following words:
1. Scavenger
2. Producer
3. Consumer
4. Decomposer
Complete the following sentences with the word or words that best fit.
5. Secondary consumers are eaten by _________________________________________.
6. Produes use energy from the _______________________________ to make their own
food.
7. The producers in lakes and oceans are _____________________________________.
8. Organisms that eat only producers are called
_______________________________________________.
Next to each consumer below, tell whether it is an herbivore by writing an H, a
carnivore by writing a C or an omnivore by writing an O. Remember each organism
can only be one type of consumer.
Organism
H, C or O
Organism
9. wolf
13. horse
10. hawk
14. human
11. Black bear
15. weasel
12. sheep
16. cat
H, C or O
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Part D What are food chains, webs and pyramids?
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The organisms in an environment are related by how they get their food. A food
chain is a way of showing these food relationships. Every organism is part of a food
chain. The picture to the left shows a food
chain. The arrows in the food chain show
the direction that food and energy moves
along the chain.
This food chain starts with grasses and
seeds. They are the producers in the food
chain. A producer always starts a food
chain. The mouse is the primary
consumer, the cat is the secondary
consumer. When the cat dies, the
mushrooms are the tertiary consumers.
A food web is a more complete
way to show feeding relationships. Since
the cat in the food chain above eats more than just mice, it would be better to show all
the things the cat eats. Ecosystems are not as simple as a food chain so we should
show as many food relationships as possible. A food web shows how a number of food
chains are related. The figure below shows a food web.
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Notice that the owl has lots of choices to eat, a rat, sparrow, sandpiper etc. Many
organisms in a food chain eat more than one type of food. Many organisms also are a
food source to more than one organism.
An energy pyramid shows how energy moves through a food chain. The figure to
the right shows an energy pyramid.
Notice that the producers are at the
bottom of the pyramid. The producer
layer has most of the food and
energy in the pyramid. Animals gain
only a small amount of energy from
the food they eat. So, as you move
up the pyramid, the amount of
energy decreases. Less energy
means fewer organisms can be
supported at each level. The tertiary
consumers are at the top of the
pyramid. There can only be a few
top-level consumers in any ecosystem
since there would have to be lots of
the organism below them to support
them.
Part D What are food chains, webs and pyramids? Review
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1. In the food chain shown on page 6, which organism is eaten by the mouse?
2. In the food web shown on page 6, which organisms eat the grasshoppers?
________________________________________
________________________________________
________________________________________
________________________________________
________________________________________
3a. Minnows are small fish that eat plant materials. Bass are large fish that feed upon
minnows. Would you expect to find more minnows or bass in a pond?
b. Give a reason for your answer.
Use the food web listed on page 6 to answer the following questions.
3. Which organisms in the food web on page 6 are producers?
_____________________________________
______________________________________
4. Is a rat a primary, secondary or tertiary consumer?
Fill in the following blanks with the word or words that best completes the sentence.
5. A food chain always begins with a __________________________________________.
6. The top of an energy pyramid contains
____________________________________________.
7. Arrows show the flow of ________________________________________ in a food chain.
8. The relationships between food chains are shown in a
______________________________________________________________.
9. The layer of an energy pyramid that has the most food and energy
contains______________________________________________.
Part E Relationships in a community
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The relationships between organisms in a community are important to figure out
what the niche of the organism is. We have already talked about one of the
relationships when we talked about a weasel eating a rabbit. That is a predator-prey
relationship.
In a predator-prey relationship, one animal is the hunter or predator and the
other organism is the hunted or prey. This relationship only works for animals. Not much
skill involved in “hunting” plants since they stay pretty much in one place. An example
of a predator-prey relationship is an owl and a mouse. The owl hunts and kills the
mouse for food. One organism definitely benefits at the expense of the other.
Sometimes organisms live so closely together that they have very close symbiotic
relationships. A symbiotic relationship is one in which two organisms have a connection
based on living very, very closely together. There are several kinds of symbiotic
relationships.
In the first type of symbiotic relationship, both organisms benefit from living
together. This relationship is called mutualism since
both organisms mutually benefit. An example of this is
lichen which you have probably seen growing on rocks
or on tree in moist areas. A picture of lichen is found to
the right. A lichen is actually two different organisms, a
fungus and an algae. Neither of the organisms can live
in these places without the other one. The algae
produces food for the fungus and the fungus gives the
algae a place to live. Nice.
The second type of symbiotic relations is called
commensalism. In commensalisms, one organism benefits but the other neither benefits
nor is harmed. An example of commensalism is the clownfish and the anemone
pictured to the left. You may remember the
clownfish from the movie “Finding Nemo”. Nemo
was a clownfish. A clownfish gets protection by
living among the anemone’s stinging tentacles.
The anemone does not benefit from the clownfish
living there. The anemone is not harmed either.
The third type of symbiotic relationship is not
so nice. In parasitism, one organism benefits at
the expense of another. An example of
parasitism is a tapeworm living in your dog or cat.
The tapeworm sucks up the food your pet has
digested robbing your pet of nutrients while the
tapeworm gets bigger and bigger. Yuck.
Part E Relationships in a community Review
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1. Define symbiotic relationship.
2. Name three types symbiotic relationships.
a.
b.
c.
3. What is the relationship called when one organism hunts, kills and eats
another organism?
4. Which relationship benefits one organism but the other is not harmed
or benefited?
5. Which relationship benefits both organisms?
6. Which relationship has one organism living at the expense of another
organism? (one is benefited and the other is harmed)
7a. Which type of symbiotic relationship would a tick on a dog be?
b. give a reason for your answer.
Part F Population Ecology
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A population is a number of the same organisms that live in the same place at
the same time. Ecologists are interested in populations. They study why populations
grow and how can we predict how big our population will be in the future? Many
characteristics of population growth are the same for other organisms as they are for
humans. By studying population growth in other species, you may be able to come up
with answers to these questions.
Part A Population Changes
Weeds!! Those pesky little plants are a real
problem to gardeners. Look at the picture of the
field of dandelions to the right. Why do these
plants crop up so quickly and in such large
numbers?
We can study how populations of
dandelions grow to understand how our own
population will grow. All populations--whether
human, plant or animal--are always changing.
Changing with the environment
Ecosystems are always changing. Sometimes they change quickly as in the case
of fire or flood. They also can change slowly. As young saplings grow into adult trees
that shade the ground below them, shade-loving plants slowly replace grasses.
Changes in an ecosystem affect the communities of organisms that live there.
Ecologists study ecosystem changes and they see patterns that help explain how the
ecosystem has developed. The patterns can be used to predict what might happen if
an ecosystem is messed up. Limiting factors are one thing that affects an ecosystem.
Limiting factors
Why do more organisms live in near the equator than near the North Pole? You
would probably say that it’s warmer and easier to find food near the equator. Food
and temperature are examples of limiting factors. Limiting factors are anything in the
environment that keeps a population from growing forever. Limiting factors can be
abiotic or biotic. An abiotic limiting factor is any non-living thing that keeps numbers of
organisms in check. For example, a grass population will increase if it has lots of
sunshine but will decrease if the area not getting any rain. The amount of rain is an
abiotic factor. A biotic factor is any living thing that keeps a population from increasing
forever. For example, the deer population in Maine is kept in check or is limited by how
many hunters get their deer. The hunters are a biotic factor.
Because all members of a food web are connected, factors that limit one
population in a community may also have an effect on other populations. For
example, a lack of water could limit the growth of grass. The population of rabbits that
eat the grass might decrease since there isn’t as much grass. What about hawks that
feed on rabbits? Their numbers may be reduced too as a result of a decrease in their
food supply.
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Name:_____________________
Date:______________________
Part F Population Dynamics Review
1. What is a population?
2. What is the name given to anything in the environment that keeps a population
from growing out of control?
3. Give an example of a biotic limiting factor for a robin population.
4. Give an example of an abiotic limiting factor for a pine tree.
5. What is the word that means a living organism that keeps a population from
growing out of control?
6. What is the word that means a non-living factor that keeps a population from
growing out of control?
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Part G Principles of Population Growth
How and why do populations grow? Population growth is the change in the size
of a population with time. Scientists use many ways to investigate population growth in
organisms. Through many population studies, scientists have seen clear patterns in how
and why populations grow.
Dollars paid
How fast do populations grow?
What’s interesting about the growth
of a population of living organisms is that it
Hours worked vs. Dollars paid
is different from the growth of some other
familiar things. Think about the growth of a
50
weekly paycheck for an after-school job.
40
Pretend you are working for a company
30
that pays you $5 per hour. You know that if
20
you work for 2 hours, you will be paid $10; if
10
you work for 4 hours, you will be paid $20; if
0
you work for 8 hours, you will be paid $40;
0 1 2 3 4 5 6 7 8 9 10
and so on. If you draw a graph of your
hours worked
paycheck growth, it would look like the
graph to the right. You can see that the
graph is a straight line.
Populations of organisms do not have straight line growth. Population growth
looks more like a J-shaped curve. The beginning change is not so great because there
aren’t that many organisms reproducing. Soon
the growth rate increases quickly because the
total number of organisms that are breeding
increases. The graph to the left shows this
exponential growth. Exponential growth of a
population of organisms occurs when the number
of organisms rises at an ever-increasing rate. The
population growth seen in the graph to the left
shows a population explosion.
Limits of the environment
Can a population of organisms grow forever? What keeps the world from being
overrun with all kinds of living things? Populations do have limiting factors in their
environment, such as food and space. A population will level off around the number
that the area can support. The number of organisms of a population that a particular
environment can support over forever without destroying the environment is known as
its carrying capacity. If a population is under its carrying capacity it will grow. If It is
over its carrying capacity it will shrink. If the population temporarily overshoots the
carrying capacity, there will be more deaths than births until population levels are once
again at the carrying capacity.
Part H Population Density
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All organisms need a certain amount of space to live in. Some organisms need a
very, very small space like a bacteria. Some organisms need a very large area like a
caribou. They not only need space to physically be on, they need space to gather
food from. Space is a limiting factor for a population.
To describe how many organisms are in an area, scientist use population density.
Population density is the number of organisms in a given area. You can figure out how
population density by using the following formula:
Population Density = Number of Organisms
area
To figure out the area you need to multiply length by width. Make
sure you use the correct units when reporting the population density.
To figure out how to calculate population density, let’s do a problem.
Problem # 1 200 ladybugs are living in a shed that is 10 feet by 10 feet.
What is the population density of the ladybugs? Make sure your answer
has the right units on it.
SolutionFirst you need to find the area the ladybugs are living in.
Area = length x width
= 10 feet x 10 feet
= 100 feet2
Second you need to put the numbers in the density formula
Population density = Number of organisms
Area
From the problem
=
200 ladybugs
100 ft2
From your calculations
=
2 ladybugs /
ft2
Problem #2 35 llamas live in an area that is 5 miles by 7 miles. What is the
population density of the llamas? Make sure you have the right units on it.
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Name:_______________________
Date:_________________________
Population Density Problems
Figure out the population density for each problem. Make sure you use the right
units in your answer.
1. Two years ago there were 48 students in Mrs. Bolvin’s and Mr. Martin’s
classrooms. What is the population density of one classroom? Give your
answer in students/classroom?
2. In June of 2000, there were 560 dandelions in an area of a field that
measures 9 meters by 6 meters. What is the population density in
dandelions per m2.
3. What is the population density of 400 robins living on 40 acres of land?
4. If there are 186 armadillos living in 62 square miles of Texas, what is the
population density? Give your answer in armadillos per square mile.
5. 20 bears live in 4 square kilometers. What is the population density in bears
per square kilometer?
6. 900,000 grass plants live on the football field. If a football field is 50 yards
wide and 100 yards long, what is the density of the grass plants in plants per
square yard?
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Name:____________________
Date:______________________
Part I The Environment Limits Population Growth
Limiting factors, you remember, are biotic or abiotic factors that
decide whether or not an organism can live in an environment. Limiting
factors also decide the size of a population. Limited food supply, extreme
temperature, and even storms can affect population size. Ecologists have
put limiting factors into two groups: density-dependent and densityindependent factors.
Density dependent factors have a greater effect in populations that
have lots of organisms in a small space. They include disease, competition,
and parasites. These things have a greater effect when populations are
very densely packed. Disease, for example, spreads more quickly in a
population whose members live close together. In crops like corn or
soybeans, in which large numbers of the same plant are grown together, a
disease will spread quickly throughout the whole crop. In less dense
populations, fewer individuals may be affected.
Density independent factors affect all populations, regardless of their
density. Most density-independent factors are abiotic factors such as
temperature, storms, floods, drought, and habitat destruction. An example
of a density independent factor is flood. No matter how many worms are
living in a field, they will all drown if the field floods.
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Name________________________
Date:___________________________
Part I The Environment Limits Population Growth Review
For each of the following tell whether it is a density dependent factor or a density
independent factor.
1. Earthquake
______________________________________
2. Food supply
______________________________________
3. Colds and Flu
______________________________________
4. Competition
______________________________________
5. Forest Fire
______________________________________
6. Hurricane
______________________________________
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Part J Reading Population Graphs
Graphs of population are very interesting. They give us lots of information in a
nice picture form. For any date you can find out what the size of the population is.
Look at the graph below to see how this works.
Days vs. # fruit flies
100
90
80
# fruit flie
70
60
50
40
30
20
10
0
0
5
10
15
20
25
30
35
40
45
days
By looking at the graph, you can see on day 10, the population is 10 fruit flies. You can
tell this by finding day 10 on the graph, following a line up to the graphed line crosses it.
Then you need to follow the line to the y axis to find out how many fruit flies were alive
on day 10.
Use this method to find out what the population is on day 25. Did you get 100
flies? If you didn’t, see your teacher for help.
Another piece of information you can get from this graph is the carrying
capacity. Remember the carrying capacity is the largest number of animals an area
can support for ever. The population builds quickly just before the carrying capacity.
When the resources like food and space are gone, the population will start to die off.
When the carrying capacity of an area is reached, it is the highest point of the graph.
The graph drops quickly after the carrying capacity. The carrying capacity of the fruit
flies is 100 flies since it is the highest point.
Another piece of information you can get from the graph is when the population
is in homeostasis. Homeostasis is when the number of organisms coming into the
population is the same as those leaving the population. You can tell the population is in
homeostasis because the line is almost flat. The population is in homeostasis around 20
organisms. You can tell this since the graph is just about flat from day 35 to day 45.
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Name:__________________________
Date:____________________________
Part J Reading Population Graphs Review
Look at the graph below and answer the following questions.
Year vs. # Coyotes
90
80
# coyote
70
60
50
40
30
20
1950
1955
1960
1965
1970
1975
1980
1985
Year
1. How many coyotes were in the population in 1995?
2. How many coyotes were in the population in 1960?
3. What is the carrying capacity of the area?
4. In what year was the coyote population 60?
5. In what years is the population in homeostasis?
6. in what year is the coyotes population 40?
1990
1995
2000
Part K Rates that affect Population Size
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The amount of food, water, space and air are limiting factors for any
population. If there are lots of these things in an area, members of the
population will reproduce and increase the population. Also, organisms
from other areas may move into the population to take advantage of the
extra supplies.
When resources are in short supply or are gone, organisms have a
couple of choices. They can stay put (and probably die) or they can
leave the population in search of another place that has the resources
that it needs.
These four things affect the size of a population. Scientists call the
rate at which organisms are being born as natality. They also call the rate
that organisms move into a population as immigration. Both of these things
have a positive effect on a population. Scientists call the rate organisms
are dying in a population mortality. They also refer to the rate that
organisms are moving out of a population as emigration.
If you know these 4 rates, you can figure out how big a population will
be in the future and how big it was in the past. You need the following
formula to figure this out.
Growth rate = natality – mortality + immigration –
emigration
Let’s see how this formula works.
Problem #1 Figuring out the Growth Rate
A population of squirrels has 20 squirrels born per year. It also has 10
die per year. 15 squirrels per year come into the population to take
advantage of the large acorns found in the area. 5 squirrels per year leave
to find mates in a different population. What is the growth rate of the
population?
Solution –
First figure out what the 4 rates are:
Natality = 20 squirrels / y
Mortality = 10 squirrels / y
Immigration = 15 squirrels /y
Emigration = 5 squirrels / y
Second you need to put the four rates in the formula:
Growth rate = natality – mortality + immigration – emigration
=
20 - 10
+
15
5
=
10
+
10
=
20 squirrels per year
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You can use the growth rate you just calculated to figure out how many
squirrels there will be in the future or in the past. You just need to know the
current population.
Problem #2 Predicting Future Population Size
The current population of the squirrels from problem 1 is 100 squirrels.
What will the population be 5 years from now?
You need another formula:
Population Size = current population + (# years
x
growth rate)
Remember to multiply years times growth rate before you add it to
the current population.
= 100
+ (5 y x 20 squirrels/y)
= 100
+ ( 100 squirrels )
= 200 squirrels
You can use the same formula to find out what the population was in the
past. Instead of using positive time units, you use negative units. For
example if you want to find out what the population was 3 years ago, you
would use a -3 years for your time units in the formula.
Population Size = current population + (# years
x
growth rate)
Problem #3 Predicting Past Population Size
What was the squirrel population 3 years ago?
Use the formula and put the numbers in.
Population Size = current population + (# years
x
growth rate)
= 100 squirrels
+ ( -3 yrs x
20 squirrels /yr)
= 100 squirrels
+ (-60 squirrels)
= 100 – 60 squirrels
= 40 squirrels
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Name:________________________
Date:___________________________
Part K Rates that affect Population Size Review
Rachel counted all the earthworms in a square meter in her back yard and found
she had 36. She went back a week later and found she had only 30. Rachel knew
that this was far too few to maintain her lawn so she decided to study the population
for a couple of weeks. She found there were 9 worms born per week and 5 died per
week. She also found 10 left for a nearby plot of land and 8 worms came from
nearby plots during that week.
1. Was the population growing or shrinking?
2. What was the growth rate of the population? Give your answer in worms per
week.
3. If she returns 2 weeks after she had 30 worms, what will the worm population be?
Marine biologist Adena sees 100 jellyfish at the end of the Old Orchard Beach pier.
Having studied the local jellyfish population, she knows the area loses about 3 jellyfish
per day to a neighboring cove but 10 jellyfish per day migrate into the population.
She knows 5 jellyfish are born per day and but 2 die each day.
4. What is the rate of growth of the jellyfish population? Give your answer in jellyfish
per day.
5. What will the population be in 10 days? The growth rate is constant.
6. If the growth rate is constant, how many jellyfish lived at the end of the pier 10
days ago?
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Part L Average Annual Increase
Another piece of information you can get from a graph is the average annual
increase or decrease in a population. You can figure this out by reading the graph
and using the following formula:
Average change = (Final population – initial population)
#time units
Again you have to do the math in the ( ) before you divide by the # years.
How do you use this formula? Let’s do a problem using the fruit fly graph.
Days vs. # fruit flies
100
90
80
# fruit flie
70
60
50
40
30
20
10
0
0
5
10
15
20
25
30
35
40
45
days
What is the average daily increase in the fruit fly population for the 10 days between
day 0 and day 10?
Use the formula: Average change = (Final population – initial population)
#time units
The Final population you find out from the graph by looking at day 10. It is 10 fruit flies.
The initial population you get the same way. It is zero. The number of days is 10.
Average change = (10 - 0) / 10 days
= (10) / 10 days
= 1 fruit fly /day
Now you try:
What was the average change in the population for the 10 days between day 15 and
day 25?
Did you get 8.5 flies /day? If you didn’t get that number, see your teacher for
help.
Name:________________________
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Part L Average Annual Increase Review
Use the following graph to calculate the average change in the population. You need
to use this formula: Average change = (Final population – initial population)
#time units
Year vs. # Coyotes
90
80
# coyote
70
60
50
40
30
20
1950
1955
1960
1965
1970
1975
1980
1985
1990
1995
2000
Year
1. What was the average change in the population for the 10 years from 1950 to
1960?
2. What was the average change in the population for the 10 years from 1960 to
1970?
3. What was the average change in the population for the 5 years between 1970
and 1975?
4. What was the average change in the population for the 15 years from 1985 to
2000?
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