Transcript Populations – Limits to Growth[1]

Ch 8 Populations
Limits to Growth
IDENTIFY DENSITY-DEPENDENT AND DENSITYINDEPENDENT LIMITING FACTORS THAT AFFECT
POPULATIONS IN AN ECOSYSTEM.
Video clip on Limiting Factors
First, we are going to watch this quick video on
limiting factors! Pay attention 
 http://www.youtube.com/watch?v=CuwrZUTeEqM
Limiting Factors
 DefinitionA
factor that causes population growth to
DECREASE
 A resource base that is limited can also affect the
long-term survival of a species
 Examples?
Density-Dependent Factors
 A limiting factor that depends on population size is
called a density-dependent limiting factor.
 In general, density-dependent factors are biological
factors
 Some examples of this include competition,
predation, parasitism, and also disease
Density- Independent Factors
 Definition- This is when all populations are affected
in similar ways, regardless of the population size.
 Examples?
 Unusual
weather, natural disasters, seasonal cycles,
and certain human activities—such as damming
rivers and clear cutting forests
Activity- Application
 Get in groups on 3 or 4 for this activity
 Read the passage “Yellow Perch in Lake Winnepig”
aloud (each student should follow along throughout
the passage)
 Answer the questions that follow in your group on
your OWN SHEET OF PAPER (everyone must have
their own sheet to turn in)
Activity Questions 1 & 2
1) Explain the difference between density independent and density
dependent limiting factors.
2) From the previous article “Yellow Perch in Lake Winnipeg”,
identify and describe as many limiting factors as possible and
classify them as density independent or density dependent.
Density Independent
Density Dependent
Activity Question 3
3) Each of the statements below involves a situation that will affect
the growth of a population.
Classify each of the statements as DD (density dependent) or DI
(density independent) and give a reason for your choice. (18
marks - 2 each)
a. Rainbow smelt and yellow perch attempt to occupy the same
area. The more aggressive smelt survive; the perch do not.
b. A severe flood brings a lot of sediment and silt into Lake
Winnipeg. The turbidity of the lake increases greatly.
c. A drought decreases the water level in Lake Winnipeg. The
carrying capacity of the lake decreases.
Activity Question 3
d. Due to the introduction of rainbow smelt, Lake
Winnipeg becomes crowded and some fish species do not
survive.
e. Since northern pike prey on yellow perch, an increase in
the perch population causes an increase in the pike
population.
f. Many fish die due to an increase in water temperature.
g. Due to over-fishing, the number of walleye in Lake
Winnipeg decreases.
h. A population is growing quickly when parasites cause
disease to spread quickly.
i. Since lake sturgeon migrate long distances to spawn,
many do not survive the trip.