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Chapter 19.1: Populations
1. What defines a population?
2. What factors affect the size of a population?
Focus Questions
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.
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 abioticfactors 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.
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
Populatio
n
Comm
unity
Ecosy
stem
Biosp
here
0 0 000
45
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.
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.
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
Which of these refers to anything that restricts the size of a population?
A. population density
B. limiting factor
C. carrying capacity
D. biosphere
populatio
n densit
y
limiti
ng fact
or
carry
ing ca
pacity
biosp
here
0 000
45
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. FoodSunlig
ht
Natura
l disa
sters
Tempera
ture
Populatio
n
Predato
rs
Disease
s
Food
0 0 0 0000
45
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.
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.
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.
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
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).
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 Pa
ram
eciu
m/m
L
6 Pa
ram
eciu
m/m
L
65 P
aram
eciu
m/m
L
6 Day
s
18 D
ays
0 0 000
45
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.
The carry
ing ca
pacity
will
...
The carry
ing ca
pacity
will
...
The carry
ing ca
pacity
wil.
..
The carry
ing ca
pacity
wil.
..
0 000
45
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
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