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Populations
Populations – focus questions
How does a change in one population affect another
population?
What is the biotic potential of a species?
What factors affect the biotic potential of a species?
What is environmental resistance?
What factors contribute to environmental
resistance?
Factors which can limit the growth of a
population include:
 Predation
 Shortage of food
 Disease
 Lack of water
 Lack of space
 Disaster
 Contamination of the
 Loss of habitat
Environmental
Resistance :
Carrying Capacity
“The largest number of individuals in a
species that an environment can
support”
4 factors that determine carrying capacity:
1.
2.
3.
4.
Materials/energy
Food Chains
Competition
Density
Materials and Energy
All populations are limited by the
availability of resources:
 Energy
(from the sun)
 Water
 Oxygen
 Carbon
 Nitrogen
 Other
nutrients
Food Chains
The Pyramids of Biomass, Energy, and Numbers
demonstrate how the population of a given organism
is limited by:
its position in a food chain/web
 the population size of those populations above and below it

Relationships:
Producer – consumer - decomposer
Predator - prey
Competition
 Ecosystems have limited resources.
 Organisms with similar needs must compete to get
the resources they need.
Supply versus Demand
Competition occurs between:
Members of the same species = Intraspecific competition
 Members of different species = Interspecific Competition

Density



An organisms’ need for space depends on their
size, environment, and way of life.
Different species have different needs for space.
This need for space determines how many
individuals of a given species can live in the same
area at the same time.
1.
2.
Factors affecting population size may be:
Density-Dependent Factors
Density-Independent Factors
Density Dependent Factors
If population density increases, it can cause a decrease
in the population.
Overcrowding leads to:
Increased stress = spread of disease and parasites
 Increased aggression = neglect of offspring
 Reduced access to resources, mates and habitat

Increased death rate/decreased birth rate =decrease
in population
Density Independent Factors
Events that can decrease population size that are not
related to how many individuals are in the population
to begin with:
 Forest fire
 Flood
 Volcano
 Extreme weather (ex. Hurricane)
 Pollution
 How do humans manage biological variables to affect
the carrying capacity of an ecosystem?
Population Growth Curve
Carrying
Capacity
Earth as Easter Island
 What is unique about Easter Island’s location?
 Describe what the first European explorers encountered





upon arrival at Easter Island.
How have the biotic factors on Easter Island changed over
time?
How has this affected the population?
How do scientists know that many species of extinct plants
and animals used to live on the island?
What did the islanders use the trees for?
How did the absence of trees affect the soil? Drinking
water? Agriculture?
Lessons from Easter Island?
Resources
 Biotic Potential and Carrying Capacity of a
Population