How Populations
Change in Size
Section 8.1
Objectives:
1.
Describe factors affecting
population growth.
2.
Describe regulation of
population size in nature.
3.
Describe the relationship
between carrying capacity and
population size.
Two Types of Growth


You have just been offered a job that will
last one month. You have two salary
options. You can either receive $10 a
week with a $5 per week raise every week,
or you can receive one penny for your
first day on the job, and then double the
previous day’s pay for each of the
remaining 30 days.
Calculate your month’s pay for each
salary option. Which pay option would
pay more?
What Is a Population?


Definition: all members of a species living
in the same place at the same time
Examples of populations in your
neighborhood:
Properties of Populations
Size
Density
1.
2.


Dispersion
3.



The number of individuals per unit area or
volume
EX: number of bass per cubic meter of water
in a lake
The distribution or arrangement of a
population’s individuals within a given space
Can be even, clumped, or random
Classroom Density activity
Classroom Density Activity

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12 volunteers
Make a 2m x 2m square
All 12 students stand in the square.
Calculate the DENSITY of that population
of students - #students/m2
Expand the square to 4m x 4m.
Recalculate the density.
Which population has the higher density?
WHY?
How Does a Population Grow?



What would cause an increase in a
population?
What would cause a decrease in a
population?
Growth rate



A change in the size of a population over a
given period of time
Growth rate = births – deaths
Can be positive, negative, or zero
Quick Lab: Population Growth
(p.198) – CALCULATORS!!!
Year
Starting
Births
Deaths
Ending
1
2
3
4
5
6
7
8
9
10
Graphing Skills Review
1.
2.
3.
4.
Descriptive title
Label each axis
Even intervals
???
Post-lab Questions



What type of growth does the graph
indicate: linear growth or exponential
growth?
Calculate the 10-year growth rate using
the formula:
Growth rate = Change in population
Time
Compare this to the growth rate from Year
1 to Year 2.
How Fast Can a Population
Grow?

Reproductive potential

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The maximum number of offspring that each
member of the population can produce
Varies WIDELY
Higher if an organism produces more offspring
at once, reproduce more often, and reproduce
earlier in life
Exponential growth


Growth goes faster and faster
EX: 2 dogs give birth to 6 puppies.
Each pair then gives birth to 6 puppies.
Breck
Shampoo
Commercials
You tell 2
friends, and
they tell 2
friends, and
so on, and so
on, and so
on, ……
What Limits Population
Growth?
1. Carrying capacity:
a. the maximum population that an
ecosystem can support indefinitely.
b. Can be determined by available food,
shelter, or breeding sites.
c. See Figure 5, p.200
Chapter 8
Population Changes & Carrying
Capacity
What Limits Population
Growth? (cont.)
2. Resource limits – a population cannot
consume more of a resource than is
available.
3. Competition within a population –
a. As a population reaches its carrying
capacity, its members must
compete with
each other for resources.
b. They may also compete for dominance or
for a territory.
Two Types of Population
Regulation
Density dependent
1.


Deaths occur more quickly in crowded
populations
Causes: limited resources, predation, and
disease
Density independent
2.


Certain number of deaths regardless of
density
Causes: severe weather and natural disasters
Self-Check Quiz
1.
How are disease and predation densitydependent?
2.
What are some examples of resources
that could determine carrying capacity in
an ecosystem?
Assignment #44
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Math Practice (p.201)
Section Review (p.202): 1, 3, 6
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Answer in complete sentences!
For Question #6, read the Ecofact on page 200
and the last paragraph on page 200. Draw a 2circle/oval Venn diagram to compare the two
histories.