Download Carrying Capacity of Ecosystems

Carrying Capacity of
Ecosystems
Tip Group #1
Nancy Lennon, Robin Daham, Jennifer
Polignone
Unit Objective
Students will be able to describe the
factors that affect the carrying capacity
of environments.
Unit Components
This unit will run over the course of 4
days, 84 minute classes (block
schedule).
Unit will consist of lecture/notes,
discussion, “clicker” activities, and
outside reading.
Day One
Populations within
Ecosystems
Populations (group of organisms of a
single species living in a given area)
within ecosystems grow, shrink, or stay
the same based on the how many are
born (birth rate), die (death rate), join
(immigration), and leave (emigration)
over time.
Exponential Population
Growth
Exponential growth occurs when
resources are unlimited and
environmental conditions are ideal.
Birth Rate >>> Death Rate
J-shaped curve results when number of
organisms over time is graphed
Exponential Growth Curve
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However, in most
ecosystems….
Resources are NOT unlimited….limiting
factors slow population growth by increasing
death rate and decreasing birth rate.
Is demonstrated in the Logistic Model of
Population Growth which incorporated
limiting factors and recognizes a carrying
capacity in each ecosystem.
Results in an S-shaped curve (Sigmoid)
when number of individuals over time is
graphed.
Logistic Model of Growth…..
Carrying Capacity (K)
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What is meant by the
carrying capacity of an
ecosystem?
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Carrying Capacity
is….
The total number of individuals the
environment can support over an
indefinite period of time.
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Carrying Capacity (K) is reflected
in the Logistic Model for
Population Growth……
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What determines the carrying
capacity?
Limiting factors control the growth of
populations.
Some limiting factors are density-dependent
and others density-independent.
Ecosystem composition of plants and
animals is determined by various abiotic
factors, as well as biotic factors that act as
limiting factors to growth.
Disruptions of any of these factors shift the
carrying capacity of ecosystems.
How do limiting factors work?
Population
Size
can be limited by
Natural
disaster
Competition
Unusual
weather
Predation
Parasitism
and disease
Abiotic Factors…..
The physical components of an
ecosystem.
Any nonliving part of the environment.
Example:
A bullfrog is affected by water availability,
temperature, and humidity.
Abiotic Factors that influence
carrying capacity…
Temperature
Precipitation
Soil composition
pH
Humidity
Salinity
Amount of sunlight
Availability of nitrogen
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•The importance of each
factor varies from
environment to environment.
•Abiotic factors vary from
region to region and over
time.
•For example, temperature
varies from hour to hour, from
day to day, from season to
season, and from place to
place.
•Subtle differences (i.e. from
shade to full sun) makes a
tremendous difference in
terms of plant composition.
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Abiotic Factors as DensityIndependent Limiting
Factors…
Density-Independent limiting factors
limit population growth in similar ways
no matter how dense the population is
at the time.
Unusual weather (hurricanes, drought,
floods) and natural disasters (wildfires)
act in this way.
These factors often result in a
population “crash.”
Biotic factors…..
The biological influences on organisms.
Any living part of the environment with
which an organism may interact.
Example:
Bullfrogs may be affected by the algae it
ate as a tadpole, insects it eats as an
adult, herons that eat bullfrogs, and other
species it competes with for food and
space.
Biotic Factors that influence
carrying capacity….
All biological aspects of an ecosystem
fall into this category.
Vegetation composition often
determines what species will be
attracted to a given area due to food
availability.
Scientists note that competition,
predator-prey relations, mutualism, and
host-pathogen interactions are critical
to consider when accessing carrying
capacity.
Concept Check
You will have 2 minutes to discuss the
following question with the person
sitting next to you and formulate a
logical response.
Write your response on a piece of
paper or on your white boards
(provided by your teacher).
Compare abiotic factors with
biotic factors and give two
examples of each.
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End of Lecture for Day 1
Students will spend the rest of class on
the activity explained on the next slide.
Day 1 Activity…..
“How many raccoons can live in the
forest?” Activity
Tonight’s homework……
You will read several sections in the
text, define vocabulary, and answer
review questions. This assignment will
be due on Day 4.
Day Two
Form a hypothesis to the
following….
What factors might cause the carrying
capacity of a population to change?
You have 2 minutes to construct your response.
Write your hypothesis in your notebook.
Biotic Factors in greater detail..
Competition for resources
Symbiotic Relationships
Predator/Prey interactions
How does competition shape
communities and affect
carrying capacity of
ecosystems?
Competition for Resources
Interspecific Competition= an interaction in
which two or more species use the same
resource.
Examples: when lions and hyenas compete
for zebras,and when different plants in a
forest compete for soil and sunlight.
Often competition results in the reduction or
complete elimination of one species from the
area due to competitive exclusion.
Gause’s Paramecium Study
To illustrate the principle of competitive
exclusion.
When Paramecium caudatum and
Paramecium aurelia grew in separate
test tubes, they thrived.
However, when grown together,
P.caudatum died out because P.aurelia
was a more efficient predator of
bacteria.
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Connell’s Barnacle Study
An example of resource partitioning was
demonstrated by Joseph Connell on
barnacles off the coast of Scotland (1960).
Semibalanus balanoides and Chthamalus
stellatus live in the intertidal zone, exposed to
dessication at regular intervals.
Chthamalus tends to live higher up on rocks
than Semibalanus? Why when it can tolerate
both regions (high and low on the rock)?
Connell explored this question…
He transplanted a rock covered with
Chthamalus to lower zones in the
intertidal zone.
Soon, the rock was settled by
Semibalanus and they crowded out
Chthamalus.
Conclusion: competition restricted
Chthamalus range.
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Competition as a DensityDependent Limiting Factor
As population increases, individuals will
compete for food, water, space,
sunlight, etc.
The more crowded an area is, the
sooner resources will be used up.
Those individuals who are better
competitors survive and reproduce,
those who aren’t, die out (survival of
the fittest).
Review what you have
learned….
Take 2 minutes and discuss this
question with your neighbor and
formulate a response….
What is the relationship between
competition and population size?
How do species interactions
shape communities and how
does that affect their carrying
capacities?
Symbiotic Relationships
A symbiotic relationship exists when
there is a close, long-term relationship
between two organisms.
Parasitism, Mutualism, and
Commensalism are all examples.
Disruptions to these relationships can
alter the flora and fauna of an area,
thereby altering its carrying capacity.
a. Parasitism
A symbiotic relationship in which one
individual is harmed (the host) while the
other benefits (the parasite) (+/-).
Unlike predation, the host is not immediately
killed.
Parasites can be ectoparasites (outside the
body) or endoparasites (inside the body).
The host and parasite species are in an
evolutionary “battle” to evolve better ways to
resist infection/infect more.
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http://www.funnythreat.com/funny_animal
s/tongue-eating-parasite.html
Parasitism as a DensityDependent Limiting Factor
The denser the host population, the more
rapidly parasites can spread from host to
host.
Example, pastures that are grazed upon by
too many cattle often result the cattle
becoming infested with worms passed from
one cow to another.
Example, the flu virus spreads rapidly
through schools because there are a large
number of students in one location.
Review what you have learned…..
Take 2 minutes and respond in your
notes to the following question…..
What is a limiting factor and how do
they affect the growth of populations in
a community?
b. Mutualism
A mutual relationship exists when both
individuals benefit (+/+).
Mutual relationships, such as
pollinators (ex. Bees) and flowering
plants (ex. Lilies), are vital to the
stability of some ecosystems.
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The marsupial D. gliroides
and the mistletoe T.
corymbosus have a
mutual relationship…the
marsupial feeds on the
fruits and the mistletoe’s
seeds get dispersed.
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T.corymbosus is a keystone species in this forest, being the sole
nectar producer for hummingbirds in the winter.
c. Commensalism
A relationship in which one organism benefits
while the other is neither harmed nor benefits
(+/0).
For example, barnacles that are attached to
a whale’s skin perform no known service to
the whale; however, the barnacle benefits
from consuming the food particles that are in
the water that flows over the whales body as
it swims.
barnacles
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How does predation shape
communities and affect
carrying capacity?
Predation
Because all animals are not primary
producers, they must consume other
organisms for energy and nutrients.
The predator-prey relationship is
important in shaping communities.
Organisms prey on both plants and
animals, so the herbivore-plant
relationship is just as important.
Predation…..
An interaction in which one animal
(predator) captures and feeds on
another (prey).
Predators determine the size of prey
populations and determine the places
prey can live and feed.
For example,
Birds of prey regulate the population
sizes of mice, voles, and other small
mammals.
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Predation as a DensityDependent Limiting Factor….
Predator and prey populations fluctuate up
and down over time.
When prey populations are high (birth rate >
death rate), predators have an easier time
catching them and have plenty to eat.
This often results in an increase in predator
population size (birth rate > death rate).
Prey populations will likely drop as a
result of more individuals being caught
than are born (death rate > birth rate).
As prey populations drop, predators
begin to starve, increasing the death
rate of the predator population (death
rate > birth rate).
Populations of herbivores and plants
cycle in this same manner.
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Cyclical changes of moose and wolf populations over time.
End of Day 2 Notes
Students will work on the activity
described in the following slide.
Day 2 Activity……
“Wolves in Yellowstone Park” Activity
Tonight’s homework……
Complete work remaining from today’s
activity.
Continue to work on reading
assignment due Day 4.
Day 3
Role of Invasive Species in
Carrying Capacity of
ecosystems.
What is an Invasive Species?
An invasive species is a species
(plant or animal) that is introduced to an
ecosystem, where it did not evolve in
originally, and experiences exponential
population growth.
Invasive species often experience this
growth because their new environment
lacks predators and other
environmental factors that limit their
growth in their native environments.
Why are Invasive Species
such a problem?
Foreign species often compete with native
species for food and habitat, OR they may
prey on them.
Generally, invasive competitors and
predators have a greater negative affect on
local species than native competitors or
predators.
This is often due to the fact that native
species have not evolved strategies to “deal”
with the invasive species because they have
not lived “side by side” with that species over
time.
How do Invasive Species
infiltrate new ecosystems?
Invasive (exotic) species are introduced into
new environments in a variety of ways:
Human introduction (intentionally or
unintentionally)
In the ballast of ships and boats
In produce and other shipments from country to
country
Unintentional release from aquariums, private
owners, etc.
So, what does this mean??
It means that invasive species generally end
up affecting the carrying capacity of the
ecosystem for the native species that are
affected by the invasive species.
A few examples of invasive species that have
affected the carrying capacity of ecosystems
include: the brown tree snake in Guam, the
zebra mussel in North America, water
hyacinth in Lake Victoria, and the Nile perch
in Lake Victoria.
Case Scenario #1
Nile Perch in Lake Victoria,
East Africa
Introduced intentionally to Lake Victoria
in 1960 in order to increase sport
fishing revenues.
Nile perch, a voracious predator, found
an ample supply of food in the
abundant cichlid population native to
the lake.
By 1980, the Nile perch was the
primary fish caught in the lake.
Further Affects…..
Introduction of the perch resulted in
increased deforestation for firewood for
drying the large perch caught.
Soil erosion therefore increased, resulting in
decreased clarity (increased turbidity) of the
water.
As the algae population died off due to
decreased light penetration, their
decomposition (by aerobic bacteria) resulted
in a decrease in dissolved oxygen in the
ecosystem.
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Case Scenario #2
Brown Tree Snake in Guam
Boiga irregularis (brown tree snake)
probably arrived in Guam on a U.S.
Navy ship after the end of WW II.
It found no natural enemies and its
populations exploded to over 3 million
on the island.
This nocturnal snake feeds on birds,
reptiles, and small mammals.
Further affects……..
9 of the 12 native rainforest birds are extinct
in nature
Example, the guam rail, a flightless bird, had
a population of ~80,000 in 1968 but was
extinct by 1986.
The snakes have greatly affected the
population size of many of the small reptile
and mammals on the island.
Snakes get into homes and their venom is
mildly poisonous to infants.
Snakes increase power outages by climbing
on poles and electrical wires.
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O-M-G!!!!!!
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You have 2 minutes to
discuss the following
questions with your partner
and formulate a response
What is meant by the term
invasive species?
Why are non-native species
with invasive traits a threat to
local ecosystems?
End of Day 3 Notes
Students will spend the rest of class
working on the activity described in the
next slide.
Day 3 Activity…..
For Teacher: Have students read
“What can be done about Invasive
Mussels,” about the zebra and quagga
mussels, then apply what they have
learned to this issue.
Article can be found in Miller and
Levine’s 2010 text Biology on pg.136 or
in in word document included in lesson
resources.
Teacher Notes….
Explain that ships carry water in ballast
tanks to maintain buoyancy and
stability. The waters are loaded and
unloaded as the ship travels from port
to port.
Explain that zebra and quagga mussels
can be piced up in the ballast water as
free-swimming larvae.
Student Instructions….
Read the article “What Can Be Done
About Invasive Mussels?”
As you read, apply all that you have
learned about populations and invasive
species to this issue.
Be prepared to discuss this when
everyone is finished reading.
Discussion Questions…..
Why does the population growth of
zebra and quagga mussels in Great
Lakes ecosystems differ from the
population growth of these mussels in
their native ecosystems?
How has the geographic range of zebra
mussels changed between the mid1980s and now?
Your homework tonight…..
Hand in your typed responses to the
following questions:
Research the current status of invasive
mussel populations and the approaches
being used to prevent the spread of these
and other invasive aquatic species. What
trends are zebra mussel populations
showing?
What kinds of natural population controls do
you think would manage these invasive
mussels most effectively? Why?
Day 4
Day 4---You Poured It Where? A
Case Study in Invasive Species
The case scenario is only added as an
example. Whatever we do here, I think
this day should be a lab, movie (?), or
group presentation.
References
Miller and Levine. Biology ©2010,
Pearson Education, Inc., New Jersey.
Raven and Berg. Environment, 3rd
edition, ©2001, Harcourt College
Publishers, New York.
www.googleimages.com