Bellringer
• List 3 reasons why a population
might decrease in size
Population
• Limiting Factor: A factor that causes population growth
to decrease
• 2 Types:
o 1. Density-dependent: Factors that depend on the
size of the population
• Only become limiting when the population density
becomes very high
• Effects are intensified as the pop. Density increases
o 2. Density-independent: Factors that do not depend,
or are independent, of the size of the population
• Are limiting regardless of the size of the population
• Affect all populations in similar ways
Limiting Factors
Deforestation
• Density-Independent
• Human activities
o Deforestation; over-hunting/fishing
o Effects are harmful on population regardless of size
Predation
• Density-Dependent
• Predation
o The effect of predation intensifies as the population density of predators
increases.
Disease
• Density-Dependent
• Disease
o High population densities make the spread of disease easier to transmit
Natural Disasters
• Density-Independent
• Natural Disasters
o Hurricane, tornado, flood, severe drought
o Equally devastating to populations regardless of size
Competition
• Competition:
o More members of a population = Less Available resources = More
competition
o Less members of a population = More available resources = Less
competition
Parasitism
• Density-Dependent
• Parasitism
o High densities make it easier for parasites to find hosts, and spread
diseases
Severe frost
• Density-Independent
• Weather
o Extremely hot/cold temperatures; frost
o Adversely effects all populations regardless of their size.
Creative Writing
1. Each group will work together to develop the
beginning of a story.
o Introduce your characters, setting, problem (limiting factor), and size of
population in that characters community
o Pass your story to the next group
2. Each group will read the introduction of the their
new story, and:
o Explain how the characters are being affected by the problem
introduced in Part 1 (what fears/concerns does this organism have for
his/herself and his population
o Pass your story to the next group
3. Each group will read their new story, and write its
ending:
o Explain what happened to the character and his/her population as a
result of the problem; will they be doing anything to re-build their
population?
o Explain the impact this problem had on the overall population size?