This document discusses populations in biology. It defines key population concepts like niche, habitat, and limiting factors. It describes how populations grow over time in characteristic S-curves from exponential growth to stabilizing at the environment's carrying capacity. Predator-prey relationships are examined as well as density-dependent and density-independent limiting factors. Different types of population pyramids are shown representing expanding, stable, and contracting growth. Examples of various countries' population pyramids through history are provided to illustrate changing growth patterns over time.

1. PopulationPopulation
BiologyBiology
1

2. I. Populations
A. Niche — ecological
role of a species in a
community.
B. Two different species
cannot occupy the
same niche.
C. Habitat — where an
organism lives.
Stream habitat
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3. I. Populations
D. A population is a group of
organisms that can
interbreed (same species).
E. The largest size a
population can grow
under ideal conditions is
called biotic potential.
F. Factors acting to
decreased or limit the size
of a population are called
limiting factors.
Black Sea Nettle Jellyfish
@ Monterey Bay Aquarium
Members of a population can
interbreed.
3

4. I. Populations
G. Examples of
limiting factors are:
1) Water (a)
2) Sunlight (a)
3) Temperature (a)
4) Predators (b)
5) Salinity (a)
6) Disease (b)
7) Competition (b)
8) Food (b) Lava Lake, Oregon
Plants compete for water, sunlight, space and
deal with predation from fish, birds, & man.
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5. II Population Growth Curves
 We measure the size of
a population (number of
individuals) over time.
 When this is graphed it
forms a curve called the
population growth
curve.
China Hat, near Bend, Oregon
Plants compete for water, nutrients, sunlight,
space and deal with predation from mammals
(including man) & birds. 5

6. II. Population Growth Curves
A. Increase of population size over time.
B. Unrestrictive growth results in exponential growth
represented by a J-curve.
C. Forms a characteristic curve called an S-curve.
B C
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7. II. Population Growth Curves
D. The curve is due to a change in the amount of growth
over time.
E. The highest point in the curve is the environment's
carrying capacity. This is the number of individuals
that can live in that space.
E
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8. II. Population Growth Curves
F. At this point the natality rate (# born) & mortality
rate (# dying) are equal.
G. A combination of all limiting factors is called the
environmental resistance.
F
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9. World Population
 The world population growth rate rose
from about 1.5 percent per year from
1950-51 to a peak of over 2 percent in the
early 1960s due to reductions in mortality.
 Growth rates thereafter started to decline
due to rising age at marriage as well as
increasing availability and use of effective
contraceptive methods.
 Note that changes in population growth
have not always been steady.
 A dip in the growth rate from1959-1960,
for instance, was due to the Great Leap
Forward in China.
 During that time, both natural disasters
and decreased agricultural output in the
wake of massive social reorganization
caused China's death rate to rise sharply
and its fertility rate to fall by almost half. 9

10. Predator / Prey
 Animals that kill to eat
are called predators.
 Those that are killed and
eaten are called prey.
 As populations of prey go
up populations of
predators increase.
 As populations of prey go
down populations of
predators decrease.
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11. Predator / Prey
11

12. Predator / Prey
 "When wolf populations are
high, they eat a lot of young
moose," explains Rolf
Peterson, a Michigan Tech
University biologist who's been
studying predator-prey
dynamics on Isle Royale for
decades.
 "But 10 years later, there aren't
as many old moose." Wolf
numbers then nose-dive, and
moose thrive again.
 This in turn affects the island's
vegetation: Balsam firs decline
when abundant moose eat
young trees before they can
reproduce, then rebound when
lean moose populations allow
them to reach maturity.
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13. Predator / Prey
At
Michigan's
Isle Royale
National
Park, wolf
and moose
populations
rise and fall
in connected
cycles.
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14. III. Limiting Factors
A. Population density the
number of individuals in a
given area.
B. Density — Independent
factors not effected by the
population’s density
1. Space -- the area,
geographical range
2. Weather, seasons,
climatic changes
3. Sunlight exposure
4. Fire
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Zumwalt Prairie,
near Enterprise & Joseph, Oregon
These Juniper Trees sparsely populate
the hillside of North America's largest
remaining grassland of its type. They are
competing for water and other resources.

15. III. Limiting Factors
C. Density — dependent factors effected
by the population’s density.
A. Predation (sometimes)
B. Parasitism
C. Disease
D. Interspecific Competition — two (or
more) populations competing for the
same limiting factor
E. Intraspecific Competition —
competition between members of the
same species.
F. Principle of limiting similarity — no
two species can occupy the same
niche at the same time.
15
Zumwalt Prairie,
near Enterprise & Joseph, Oregon
Deer grazing on the prairie.
They are competing with each
other. They are competing for
water, food, shelter and other
resources.

16. Interspecific & Intraspecific
Competition
Zumwalt Prairie,
near Enterprise & Joseph, Oregon
Top: Deer graze on the
prairie. They are
competing with each
other and the elk (when
in wooded area, not
often).
Below: Elk move across road
a few miles away from
the deer in a wooded
area. They are competing
the deer (when on prairie,
not often). 16

17. Types of Population Pyramids
1. Expanding / Increasing
2. Expanding / Increasing
3. Stationary
4. Contracting / Declining
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18. Population Pyramids
 Graphs show how population pyramids change over
time.
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19. Population Pyramids
Afghanistan shows classic bulging youth of growing
population.
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20. Population Pyramids
Angola classic bulging youth of growing population.
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21. Population Pyramids
China had an extreme youth bulge until the 1960s,
when it sharply curbed partly as an effect of the one-
child policy.
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22. Population Pyramids
Russia is reducing its population, declining growth.
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23. Population Pyramids
Japan is reducing its population, declining growth.
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24. Population Pyramids
United Kingdom is reducing its population, declining
growth.
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25. Population Pyramids
Mexico’s population is increasing and maybe starting to
level off.
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26. Population Pyramids
Sweden has stable growth.
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27. Population Pyramids
USA’s population is becoming stable.
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28. Population Pyramids
Canada’s population is decreasing.
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29. Current Population
 http://www.prb.org/Publications/Articles/2014/wpd
s-2014-pyramids.aspx
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30. Human Population 2009
U.S. 307,866,146
World 6,795,124,089
19:33 UTC (EST+5) Nov 05, 2009
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31. Human Population 2014
31http://www.census.gov/popclock/
8:17:30 UTC