Population Growth - Doral Academy Preparatory

 1950’s – fish farmer
introduced hydrilla
into a canal in
 Out of control
 The area inhabited
by a population is
called its
geographic range.
 Population density refers
to the number of
individuals per unit area.
 Distribution refers to how
individuals in a population
are spaced out across the
range of the population—
randomly, uniformly, or
mostly concentrated in
 Purple lupines grow
randomly in a field
among other
 The dots in the illustration
represent individual
members of a population
with random distribution.
 An example of a
population that shows
uniform distribution is
the king penguin.
 An example of a
population that shows
clumped distribution is
the striped catfish.
These fish organize into
tight groups.
 A population’s
growth rate
determines whether
the population size
decreases, or stays
the same.
 A population will
increase or decrease in
size depending on how
many individuals are
added to it or removed
from it.
 A population can grow
when its birthrate is
higher than its death rate.
 If the birthrate equals the
death rate, the population
may stay the same size.
 If the death rate is greater
than the birthrate, the
population is likely to
Which of the following is NOT one
of the factors that play a role in
population growth rate?
death rate
The movement of organisms into a range
is called
population shift.
carrying capacity.
Which of the following could describe a
population that is decreasing in size?
A) The birthrate and the death rate remain the same.
B) The death rate is becoming lower than the birthrate.
C) The death rate is constant and the birthrate is increasing
D) The death rate is becoming higher than the birthrate.
 Under ideal conditions with unlimited resources, a
population will grow exponentially.
 In exponential growth, the larger a population
gets, the faster it grows.
 If you plot the size of this population on a graph over
time, you get a J-shaped curve that rises slowly at first,
and then rises faster and faster.
 Logistic growth occurs when a population’s growth
slows and then stops (most populations experience
this type of growth)
 follows a period of exponential growth.
 Carrying capacity is the maximum number of individuals
of a particular species that a particular environment can
A) The birthrate and the death rate remain the same.
B) The death rate is becoming lower than the birthrate.
C) The death rate is constant and the birthrate is
D) The death rate is becoming higher than the birthrate.
A) logistic
B) limiting
C) demographic
D) exponential
Suppose that a species of toads is introduced
into a new environment in an attempt to
reduce the population of insects. The toad has
no natural predators in the new environment.
The toad population would most likely
increase exponentially.
increase logistically.
decrease rapidly and die out.
remain the same.
If a population grows larger than the
carrying capacity of the environment,
which of these is most likely to happen?
The death rate may rise.
The birthrate may rise.
The death rate must fall.
The birthrate must fall.
 A limiting factor is a
factor that controls the
growth of a population.
 Some depend on
population density and
others do not.
 Density-dependent
limiting factors include
competition, predation,
herbivory, parasitism,
disease, and stress
from overcrowding.
 When populations
become crowded,
individuals compete for
food, water, space,
sunlight, and other
 Competition is a
limiting factor. The more
individuals living in an
area, the sooner they
use up the available
 The effects of predators on prey and the effects of
herbivores on plants are two very important densitydependent population controls.
 This graph shows the fluctuations in wolf and moose
populations on Isle Royale over the years.
 Herbivory can also
contribute to changes in
population numbers.
 From a plant’s
perspective, herbivores
are predators.
 In some situations,
human activity limits
 Fishing fleets have
raised cod death
rates so high that
birthrates cannot
keep up. As a result,
cod populations
have been dropping.
 Parasitism and disease
are density-dependent
effects, because the
denser the host
population, the more
easily parasites can
spread from one host to
 This graph shows a sudden and dramatic drop in the wolf
population of Isle Royale around 1980.
 At this time, a viral disease of wolves, canine parvovirus
(CPV), was accidentally introduced to the island.
 Overcrowding causes
stress in populations
 Lowers ability to fight
 Causes some females to
neglect or even eat their
 Density-independent
limiting factors affect all
populations in similar
ways, regardless of
population size and
 Unusual weather such as
hurricanes, droughts, or
floods, and natural
disasters such as
wildfires, can act as
limiting factors.
A) competition.
B) temperature.
C) crowding.
D) disease.
A) a small, scattered population
B) a population with a high birthrate
C) a large, dense population
D) a population with a high immigration rate
A) earthquake
B) disease
C) emigration
D) parasitism
 Hydrilla in its natural
environment has natural
predators, but in Florida
they don’t exist.
 Efforts have been made
to control their
 The best means of
control so far seems to
be an imported fish
called grass carp, which
views hydrilla as an
especially tasty treat.
 Grass carp are not
native to the United
States. Only sterilized
grass carp can be used
to control hydrilla.