Population Dynamics
Unit 6 Lesson 3 Population Dynamics
How can a population grow or get
smaller?
• Populations change in size based on births and
deaths
• Population size = previous population size + #
births - # deaths
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Unit 6 Lesson 3 Population Dynamics
How can a population grow or get
smaller?
• Populations change in size when individuals move
to new locations.
• Immigration occurs when individuals join a
population.
• Emigration occurs when individuals leave a
population.
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Carrying Capacity
• The largest number of individuals of one
species an ecosystem can support
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Unit 6 Lesson 3 Population Dynamics
Maximum Capacity
What factors can limit population size?
• A part of the environment that keeps a
population’s size at a level below its full potential
is called a limiting factor.
• Limiting factors can be living or nonliving things in
an environment.
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Limiting Factors
• Anything that restricts or controls the
number of individuals in a population
• Usually resources
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Growth Limitations
• Resources
• Disease
• Organism
interaction
• Habitat
Size/Crowding
• Weather
When a
population
overshoots the
carrying capacity,
then limiting
factors may come
into effect.
Over time population stabilizes around the
carrying capacity
population growth over 20 years
600
population
500
400
300
200
100
0
0
2
4
6
8
10
year
12
14
16
18
20
Two types of limiting factors:
Density-dependent
and
Density-independent
Population density describes the number of
individuals in a given area.
Population Density
• Let’s say our classroom is 600 sq. ft.
In 2nd and 5th periods, there are 25
students in the class.
The population density for 2nd and 5th is
25 students/600 ft² or .04 students/ft².
In 6th period, there are only 13 students in the
class. Is the population density higher or
lower?
Density - Dependent
• Density-dependent factors include
disease, competition, predators,
parasites, and food.
• Disease, for example, can spread more
quickly in a population with members
that live close together.
Its flu season, and lots of sick students are
coming to school. They are coughing, sneezing,
and touching everything. Ten percent of students
have the flu, but are so dedicated they come to
class anyway. If the teacher wipes down every
table before every class, which class will be most
affected by the flu?
2nd and 5th periods, because they have the
greatest population density. A larger number
of students will be infected and have
opportunity to infect a larger number of
healthy students.
Density - Independent
• Density-independent factors can affect
all populations, regardless of their
density.
• Most density-independent factors are
abiotic factors, such as temperature,
storms, floods, drought, and major
habitat disruption
The school is sponsoring an event that
allows students to miss 2nd , 5th, and 6th
periods. Which classes will be most
effected?
• All equally effected! The event will
disrupt class regardless of size –
everyone will have the opportunity to
go.
Community
Interactions
Competition
• Two or more organisms that need the
same resource – within or between
populations
• All living things compete for
– Food
– Space
• Competition limits population growth
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edu
Cooperation
• Organisms working together toward a
common end or purpose
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wsroom.msu.ed
u
Predation
• Predator hunts and eats a prey species
Symbiosis
• Any close relationship between species
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Three Types of Symbiosis
• Mutualism
• both species benefit
• Parasitism
• one species benefits, the other is
harmed
• Commensalism
•
one species benefits, the other is unaffected