1. Ch. 19.1: Populations

2. Chapter 19.1: Populations
1. What defines a population?
2. What factors affect the size of a
population?
Focus Questions

3. 1. What defines a population?
• Ecology: study of all ecosystems on Earth

4. 1. What defines a population?
What defines a population?
A species is a group of organisms that have
similar traits and are able to produce fertile
offspring.

5. Biosphere
Ecosystems
Communities
Populations
Organism
•The biosphere is the part of Earth
where life exists. It extends from the
deepest parts of the ocean to high in
the air where plant spores drift.
• An ecosystem is made up of a
community of organisms and the
abiotic factors of the community.
• A community consists of all of the
populations of species that live
and interact in an area.
• Each animal is a part of a
population, or a group of
individuals of the same species that
live together.
5 levels of Environmental Organization
•Each animal is a
part of a
population, or a
group of
individuals of the
same species
that live
together.
•A community
consists of all of
the populations
of species that
live and interact
in an area.
•An ecosystem is
made up of a
community of
organisms and
the abiotic
factors of the
community.
•The biosphere is
the part of Earth
where life exists.
It extends from
the deepest parts
of the ocean to
high in the air
where plant
spores drift.

6. On what level in the environment would your
neighborhood be? (including:
you, your pets, houses, streets, yards, etc.)
A. Organism
B. Population
C. Community
D. Ecosystem
E. Biosphere
Organism
Population
Com
m
unity
Ecosystem
Biosphere
0 0 000
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7. Factors that affect the size of a population:
• Competition is the demand for resources
that are in short supply in a community.
– food, water, shelter, mates, space
• When there are
not enough
resources
available to
survive, there is
more competition.

8. 2. What factors affect the size of a population?
• Populations change as
environmental factors change
Limiting factors:
A. Sunlight availability is a limiting
factor for most organisms.
• Without sunlight, green
plants cannot make food,
which effects animals that
eat plants.

9. 2. What factors affect the size of a population?
B. Temperature is a limiting factor for some organisms.
– When the temperature drops below freezing, many
organisms die because it is too cold to carry out their life
functions.
C. Diseases
D. Predators
E. Natural disasters
– fires
– Floods
F. Food, Water,
Shelter, & Mates

10. Which of these refers to anything that restricts
the size of a population?
A. population density
B. limiting factor
C. carrying capacity
D. biosphere
population
density
lim
itingfactorcarryingcapacity
biosphere
0 000
45

11. Which of the following is NOT an example of a
limiting factor?
A. Sunlight
B. Natural disasters
C. Temperature
D. Population
E. Predators
F. Diseases
G. Food
Sunlight
NaturaldisastersTem
peraturePopulation
Predators
Diseases
Food
0 0 0 0000
45

12. 2. What factors affect the size of a population?
• Population density is the population count
in a specific area.
• One way of estimating population density
is by sample count.

13. 2. What factors affect the size of a population?
• Biotic potential – the potential growth of
a population if it had no limiting factors (if
it had perfect conditions).
• No population on Earth ever reaches its
biotic potential because no ecosystem has
an unlimited supply of natural resources.

14. 2. What factors affect the size of a population?
• Carrying Capacity (K): largest population
that an environment can support
• A population grows until it reaches the
carrying capacity of an environment.

15. 2. What factors affect the size of a population?
Carrying capacity is determined in part by
limiting factors.
Starting
to
increase
Carrying
capacity
(stabilizes)Rapid
increase

16. 2. What factors affect the size of a population?
• Carrying capacity of an environment is not constant –
it increases and decreases as the amount of available
resources increases and decreases.
• When the size of a population becomes larger than
the carrying capacity of its ecosystem,
overpopulation occurs.
• When one population
(meerkats) overpopulates,
often it results in another
population decreasing
(spiders).

17. The graph below shows the growth over 18 days of a population of
paramecia (single-celled organisms) in a test tube. The test tube
contained food. Use this graph to answer the questions that follow.
What is the carrying capacity of the test tube when
food is provided?
A. 0 Paramecium/mL
B. 6 Paramecium/mL
C. 65 Paramecium/mL
D. 6 Days
E. 18 Days 0
Param
ecium
/m
L
6
Param
ecium
/m
L
65
Param
ecium
/m
L
6
Days
18
Days
0 0 000
45

18. The graph below shows the growth over 18 days of a population
of paramecia (single-celled organisms) in a test tube. The test
tube contained food. Use this graph to answer the questions that
follow.
Predict what will happen if no additional food is provided.
A. The carrying capacity will
stay the same
B. The carrying capacity will
increase
C. The carrying capacity will
decrease, then stabilize at
a lower number.
D. The carrying capacity will
decrease and eventually
all the organisms will die.
Thecarryingcapacityw
ill...
Thecarryingcapacityw
ill...
Thecarryingcapacityw
il...
Thecarryingcapacityw
il...
0 000
45

19. Which of these increases when there
are not enough resources available in
a community for all its organisms to
survive?
A. B. C. D.
0 000
A. Competition
B. Population
C. Organism
D. Food
30

20. Which term refers to all the
populations of different species that
live together in the same area at the
same time?
A. B. C. D.
0 000
A. Population
B. Biosphere
C. Community
D. Ecosystem
30