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Leyda
1.
Geographic distribution: the area inhabited
by a population.
2. Population density: the number of individuals
per unit area.
2.
Population density: the number of individuals
per unit area.
a. high density: lots of individuals per unit area
2.
Population density: the number of individuals
per unit area.
a. high density: lots of individuals per unit area
b. low density: few individuals per unit area
3.
Growth Rate: how quickly a population
changes in size.
Fast Growth Rate:
Slow Growth Rate:
55 Minutes!
55 Years!
Birth rate
________
Death rate
________
1.
2.
stays the same
birth rate = death rate  population size _________________
increases
b. birth rate > death rate  population size _________________
decreases
c. birth rate < death rate  population size _________________
a.
movement of individuals into an area
3. immigration: _________________________________
bison immigrates to a meadow full of grass
a. example: ___________________________________________
movement of individuals out of an area
4. emigration: _________________________________
bison emigrates out of a meadow without grass
a. example: ___________________________________________
Individuals reproduce at a constant rate
Exponential growth: _________________________________
1. ______________
1.
Individuals reproduce at a constant rate
Exponential growth: ________________________________
____________
a. Conditions necessary for exponential growth
1. Unlimited resources
2. Absence of disease and predators
b. Example: Bacteria will double their population in 20 mins
Staphylococcus aureus
c. Shape of graph: J-shaped
d. Graph example:
Notice: as time goes on,
population increases
exponentially.
2.
Logistic growth: ______________________________________
Population grows rapidly until some factor
________
limits growth
_____________
a. When does population growth slow or stop?
1. Birthrate – Down
2. Immigration – Down
3. Death rate – Up
4. Emigration – Up
b. Example: Any animal population in
nature.
c. Shape of graph: S-shaped
d. Graph example:
Notice: as time goes on,
population increases
then hits a limit and
levels off. This limit is the
carrying capacity for that
population.
e. Carrying capacity: Maximum number of individuals that
an area can support.
Limiting factor: something that causes population growth to
decrease.
VS
A. Density-dependent limiting factors: When population is
high these take effect.
1. Competition: Organisms compete for food, water,
space, sunlight, and other essentials.
Example: Birds and mice both eat seeds.
Effect on Evolution: Both species are put under
pressure to change in ways that decrease
competition.
Remember Competitive Exclusion Principle!
2. Predation: One organism eats another.
Example: Lynx eats rabbit.
Predator: Lynx Prey: Rabbit
Effect on Evolution: Prey species (rabbit)
evolves
defenses (speed, camouflage), predators
evolve
counter-defenses (eyesight).
Parasitism: Organisms live in and on a host organism.
Examples: Ticks, fleas, leeches, tapeworms.
B. Density-independent limiting factors: Not related to
population size.
1. random events: Unusual weather, natural disasters:
volcanoes, hurricanes, floods, ice age
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Density-independent limiting factors: Not
related to population size.
 2. human disturbances – such as damming rivers
and clear-cutting forests.
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Lava Flow
Number of predators
Spread of disease
Especially cold winter
Toxic chemical spill into a stream
Another species competing for same
resource
Diverting river for irrigation
Beetles that attack trees