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POPULATIONS
Ch 5.1
Ecology
Population Review
• What is a population?
• Groups of individuals that belong to the
same species and live in the same area
• Give an example from a biome.
Population Characteristics
1)
2)
3)
4)
Geographic Distribution
Population Density
Growth Rate
Age Structure*
Each factor listed above is equally important in
determining the future of a population.
(ex: endangered vs. overpopulated)
Geographic Distribution
• Also called “range”
• Area (size) inhabited by a population
• Ex: Northern Cardinals and Cedar
Waxwings
Northern Cardinal
Cedar Waxwings
Population Density
• Number of individuals per unit area
• Main characteristic to describe a population
• Varies greatly depending on species and
quality of ecosystem
• Ex 1: Cacti vs. Rainforest Fig Trees….Which is more
dense?
• Ex 2: Science Daily (Dec. 7, 2000) — Nov. 22, 2000
-- Zoologists from the University of Toronto have
cracked the ecological puzzle of how animals - in this
case the arctic ground squirrel - manage to control
their own population in the northern boreal forest of
Canada.
Growth Rates
• Natural populations can grow, decline,
or stay the same
• Depends on 3 factors:
• Birth Rate
• Death Rate
• Individuals entering or leaving population
• Immigration (in) and Emigration (out)
• Give an example for the terms above!
Examples
•
What will happen to the following
population (grow, decline, stay the
same) immediately and later.
1. The EPA protects sea otters from
hunting.
2. Killer whales prey on sea otters.
Exponential Growth
•
With abundant space and food,
protection from disease and predators,
a population will increase in size
exponentially
1. Reproduce at constant rate
2. Unlimited Resources
3. Begins slowly, then takes off!
Ex: Doubling effect of bacteria
Consider this…
• Bacteria have the fastest rates of
reproduction among living things
• Assume “binary fission” (doubling) occurs
every 20 minutes
• 20 min= 2 bacteria
• 40 min= 4 bacteria
• 60 min=8 bacteria
• 120 min = 64 bacteria
• 3 hrs = 512 bacteria
• 24 hrs = 4,720,000,000,000,000,000,000
bacteria
Charting Exponential Growth
• J-shaped curve = unlimited resources
and growth
Logistic Growth
• As shown prior, exponential growth only lasts
for a short while
• Logistic growth occurs when growth slows or
stops after exponential growth occurs
• Results from:
• Birthrate drops/Death rate increases
• Immigration slows/Emigration increases
• Both can result from lack of space and resources
Charting Logistic Growth
• “S” shaped curve
• Shows “carrying
capacity” of an
ecosystem
(maximum # of
organisms based on
available resources)
• Why does the
population remain
constant towards
the end of the
curve?
Bringing it all Together!
Why is the carrying capacity
not a flat line?