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Populations
Biology
2015-2016
Populations
Objective: to understand the
way that populations of
different organisms grow and
shrink, and what factors cause
these changes in a population
http://www.worldometers.inf
o/world-population/
I. Describing a population
1. Geographic
Distribution:
the area
inhabited by a
population
Map shows the Geographic Distribution of the
California Quail 1994-2003
2. Population density:
number of individuals
per unit area
Population Density:
a. High density:
lots of individuals
in one area:
example grass
b. Low density:
few individuals
in a unit area:
example: trees
3. Growth rate: how quickly a
population changes in size
Example: Some bacteria can double
their population in minutes!

45 Minutes
3. Growth rate: how quickly a
population changes in size
Example 2: Trees can not double their
population in 45 minutes. Its takes years and
years for a population of trees to double in size.

45 years
II. Factors affecting population growth
1. Birth rate
2. Death rate
Birth = Death  Stays the same
100 Born
100 Die
b. Birth > Death  Increases
150 Born
50 Die
Birth < Death  Decreases
50 Born
150 Die
3. Immigration: movement of
individuals into an area
Example:
The Bison immigrates
to a meadow full of
grass because it
provides a good source
of food.
4. Emigration: movement of
individuals out of an area
Example:
The Bison Emigrates
away from a meadow
without grass because
it does not provide a
good source of food.
5. You must emigrate from somewhere
in order to immigrate to somewhere.

Emigrate from..
Immigrate to..
III. Types of Growth
1. Exponential Growth: individuals
reproduce at a constant rate
a. Conditions necessary for
exponential growth
1. Unlimited Resources
b. Example: Bacteria
c. Shape of graph J
d. Graph
2. Absence of
disease and
parasites
Exponential Graph
2. Logistic Growth: Population grows
rapidly until some factor limits growth
a.
When does population growth slow or stop?
1.
Birthrate:
1.
Immigration:
b. Example:
Down
Up
4. Emigration:
Up
Most animal populations in nature
c. Shape of Graph
d. Graph
Down
3. Death rate:
S
Logistic Graph
e. Carrying capacity: Maximum # of
individuals that an area can support
IV. Limits to Growth
1. Limiting Factor: Condition that
controls population size ex: food,
land
Animals in a population may not have enough food
to go around
IV. Limits to Growth
2. Competition: Two or more species
attempt to use same resource
a. example: Bird and squirrel both eat berry
b. Effect on evolution:
b. Effect on evolution:
both species under pressure to
change in ways that decrease
their competition
Bird eat worm
Squirrel eat nuts
3. Predation: one organism eats another
a. example: Mouse and Snake
b. predator: Hunter
c. prey: Hunted
3. Predation: one organism eats another
d. Effect on evolution: prey species evolve
defenses against predators, predators
evolve counter defenses
Mouse: Camouflage
Snake: forked tongue
and heat vision
4. Parasitism: organisms live and
feed inside/on a host organism
a.
examples: Fleas, ticks, leaches, tape worm
5. Random events: Unusual weather,
human activities, natural disasters.