Download Population Growth in an Ecosystem

Population Growth in an
Ecosystem
PRE AP BIOLOGY
Populations and Communities
If an organism is given the right
conditions for growth and
reproduction, there will be a
rapid increase in is population.
Exponential Growth
 If nothing stops
a population
from growing it
will show a
growth pattern
called
exponential
growth.
 Exponential growth
curves do not continue in
populations for long.
Populations that start
growing exponentially and
then come crashing down
are called boom-and-bust
populations. Insects quite
often exhibit boom-andbust population growth.
 Populations exhibiting boom-and-
bust population growth patterns are
usually regulated by density
independent factors such as
rainstorms, drought, heat , cold,
and fires. The population starts to
grow exponentially , then a fire or
something else will cause the
population to crash. When these
environmental conditions occur, they
effect the population the same way no
matter the size of the population.
Boom-and-bust organisms are called
r-strategists.
This slide goes with your notes
Write this down!!
 Exponential growth is uncontrolled growth in a ecosystem
with plenty of resources (food, space etc.) Exponential
growth cannot continue forever. Some populations grow
exponentially and then come crashing down due to density
independent factors such as rain, drought, fire etc. Size of
the population as no effect on result. Example-Insects are
regulated by density independent factors. Insects are called
r-strategists.
Write this down!!
 The population growth
rate is equal to the birth
rate minus the death rate
r=(b-d). r is called the
intrinsic rate of increase.
The population growth
rate is also dependent on
the number of
individuals present in the
population N. The total
population growth rate is
equal to G=rN
 The total population
growth rate is equal to
G=rN.
 r = (b-d) or (birth rate
– death rate) intrinsic
rate of increase .
 N is the number of
individuals present in
the population
Write this down!!
 Other populations go
through a number of growth
phases which can be shown
on a logistic growth curve.
At first the population starts
to grow slow (lag phase). It
is followed by rapid growth
(exponential growth). Then
the population growth rate
slows down until it reaches
the steady state. The
carrying capacity of an
ecosystem is the maximum
number of organisms that
ecosystem can carry without
damaging the ecosystem.
Write this down!!
 Steady state is when the birth rate equals the death
rate. Usually this happens at the carrying capacity .
There are some fluctuations at the steady state. As
the population becomes more dense, other factors
regulate the population. These include competition
for factors like food, water, space. If the competition
is within the same species it is called intraspecific
competition and if it is between two different species
is called interspecific competition. Other density
dependent limiting factors include predator-prey
interactions and simbiotic relationships.
 For about the last 500 years the human
population has grown exponentially.
 Populations in most of the world are still
growing very rapidly.
 Some scientists estimate there are
 close to 6 billion people on Earth.
 Organisms that show logistic growth curves are
called K strategists.
 r-strategist
 Produce many young
 No parental raising young
 Boom-and-bust growth
K-strategist
Fewer young
Parents invest time in
raising young
Logistic growth
curve
 Live unstable environments Lives in stable
environments
 Density independent factors Density dependent
regulate population
factors regulate
population
Predator-prey
relationships can regulate
populations
 Just about every species
serves as food(prey) for
another species(predator).

 Many predator-prey
relationships must coexist
over a long period of time.
 The two populations will
go in cycles. If one
population gets too large
or small it affects the other
population.
Write this down!!
Predator-prey relationships can regulate
populations
 Prey is what is eaten and predator is what
does the eating. The predator population
mirrors what happens to the prey population.
 Many predator-prey relationships must
coexist over a long period of time.
 The two populations will go in cycles. If one
population gets too large or small it affects
the other population.

In this Predator-prey Relationship which
population must always be greater?
Symbiotic relationships
 Some
organisms
interact in
relationships
called
symbiosis.
 There are
three types of
symbiosis
 1. Mutualism-Both
organisms benefits.
This black rhinoceros
is being cleaned of
parasites by yellowbilled ox-peckers.
 2. Commensalism
(symbiosis)- one species
benefits while the second
species is not helped or
harmed in any way
 The example is the fish and
sea anemone The clown
fish is is protected by the
sea anemone and is not
harmed by the poinson
found in the tentacles of
the anemone. In this case
the clown fish benefits and
the anemone is not harmed
or benefits in anyway.
 3. Parasitism (symbiosis)-
one species harms its host
and the other species
benefits. This is
Schistosoma mansoni, or a
blood fluke. It has 2 host,
humans and snails. It
causes schistosomiasis
which include dysentery
and anemia. Victims
become weak and succumb
to other diseases due to
their weakened condition.
Write this down!!
 Symbiosis-Organisms living together.
 Types of symbiosis

1. Mutualism-Both
organisms benefits.
2.
Commensalism (symbiosis)- one
species benefits while the second species
is not helped or harmed in any way
3.
Parasitism (symbiosis)- one species
harms its host and the other species
benefits.
 Niche-is the role of an organism in the
environment. It includes the habit, food,
predator-prey relationships. The more two
species niches overlap the greater the
competition.
 Example: two different niches
Population Ecology Review








1. What is a population?
2. Compare exponential and logistic growth
curves.
3. What limits an area's carrying capacity?
4. Identify density dependent and independent
limiting factors.
5. How do predators and prey affect each other?
6. What is a community?
7. Compare parasitism, mutualism and
commensalism.
8. Describe how ecosystems interact with each
other.