Download Organism Interactions Limit Population Size Organism Interactions

Organism Interactions Limit
Population Size
Organism Interactions Limit
Population Size
Organisms depend on each other for:
1. Predation:
Protection
Unchecked for many
years, the snakes caused
the extinction of nearly
every native bird species
on the Pacific island of
Guam
Reproduction
Food
– What could happen if a predator is
introduced to a population and there are
no organisms to eat it?
Shelter
So what happens when these
factors change?
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Organism Interactions Limit
Population Size
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Organism Interactions Limit
Population Size
2. Competition
3. Crowding & Stress
– As pop. Increase in size and start
straining their resources, they may
become stressed. What are some
examples of stress symptoms?
- What can happen if resources become
limited?
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•
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Aggression
Decrease in parental care
Decreased fertility
Decreased resistance to disease
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How do you determine human
population size?
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How do you determine human
population size?
• Growth rate—amount that a
population’s size changes over
time
Birth rate – death rate = growth rate
- Positive number means the pop. is
growing
- Negative number means the pop. is
shrinking
– Birth rate—number of births
occurring during a period of time
(ADD)
-- Death rate (or mortality rate)—
number of deaths in a period of time
(SUBTRACTS)
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What can affect population size?
Human population size
• Other things that affect a population’s
numbers:
• Life expectancy—how long on average
an individual is expected to live
• When you figure out the number of
individuals living in a certain area, this
is called the population density.
• There are two limiting factors (biotic
and abiotic) that can affect the pop.
density
• Limiting factor—any biotic or abiotic
factor that restrains the growth of a
population
– US men: 72 yrs, US women: 79 yrs
• Immigration—individuals moving into a
population (ADDS)
• Emigration—individuals moving out of
a population (SUBTRACTS)
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What are limiting factors?
• Density-independent factors—factors
that affect the population regardless of
the population’s size
– Ex: fires, climate
• Density-dependent factors—factors
whose effects on the population
depend on the population’s size
– Ex. food shortages, disease
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