Transcript Carrying Capacity of Ecosystems

Carrying Capacity of
Ecosystems
Lesson Objective
Students will be able to describe the
factors that affect the carrying capacity
of environments.
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 (emmigration)
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
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.
Carrying Capacity is….
The total number of individuals the
environment can support over an
indefinite period of time.
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
•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.
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.
Compare abiotic factors with
biotic factors and give two
examples of each.
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.
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).
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.
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.
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.
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.
How does predation shape
communities and affect
carrying capacity?
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.
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.
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.
What is meant by the term
invasive species?
Why are non-native species
with invasive traits a threat to
local ecosystems?
References
Miller and Levine. Biology ©2010,
Pearson Education, Inc., New Jersey.
Raven and Berg. Environment, 3rd
edition, ©2001, Harcourt College
Publishers, New York.
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