1. POPULATIONS

2. A population consists of all the individuals
of a species that live together in one place.

3. The area inhabited by a population is called its geographic range.
Small geographic range
Large geographic range

4. Population density refers to the number of individuals per unit area.
Two ducks
Hundreds of fish
Low population density
High population density

5. Distribution refers to how individuals in a population are spaced out across the range of the population.

6. Population size-
the number of individuals in a population.

7. Population growth – the increase in the
size of a population over time.

8. A population grows when exceed . births deaths
More births than death…population grows.
100
+20
120
-15
105
Initial population=100
Births=20
Deaths=15 +5
105
Change in population = ____
Final population= _____

9. More deaths than births…population decreases.
100
+20
120
-25 95
Initial population=100
Births=20
Deaths=25
- 5 95
Change in population = ____
Final population= _____

10. The factors that can affect population size are
the birthrate, death rate, and rate at which
individuals enter or leave the population
(immigration and emigration).
emigration - exit
immigration - in
Population
decreased
Population
increased

12. If more individuals come in (immigration) than
exit (emigration), then population increases.

13. Births and immigration add
individuals to a population
The population
increases
The population
decreases
Deaths and emigration remove
individuals to a population

14. What does a population need to grow?
food
water
space
few predators
less disease

15. Example: A single bacteria divides to produce
two bacteria every 20 min. 1 2
Time (min)
# of bacteria 20 40 60 80
100
120
140
160
180 4 1 2 8 4 8 16 16 32 64 32
128 64
256
512

16. Compare the growth rate of bacteria:
Time (min)
# of bacteria 20 40 60 80
100
120
140
160
180 1 2
1st hr
Very slowly 4 8 16
Slow-medium
2nd hr 32 64
128
3rd hr
Rapidly
256
512

17. Let’s graph the data. Exponential Growth Curve Check out the slopes
Time (min)
# of bacteria 20 40 60 80
100
120
140
160
180
Check out
the slopes 1 2 4 8 16 32 64
128
256
512

18. Under ideal conditions with unlimited resources,
a population will grow exponentially.
Exponential growth means that as a population
gets larger, it also grows faster.

19. Can a population of organisms grow indefinitely?

20. Can a population of organisms grow indefinitely?
Population growth is limited by
food
water
predators
disease
space

21. any biotic or abiotic factor that controls the growth of a population.
Limiting factors-
any biotic or abiotic factor that controls
the growth of a population.
Limiting factors are environmental factors
that affect an organism’s ability to survive
in its environment.

22. Some limiting factors may be:
water
food
predators
disease
competition
temperature
natural disasters

23. Limiting factors prevent a population
from growing exponentially forever.
Therefore, most organisms’ populations
follow a logistic growth curve, an S-shaped curve.
Check out
the slopes
Number of Organisms
Time

24. Logistic growth
occurs when a population’s growth slows and
then stops, following a period of exponential growth.

28. Phases of Growth: Phase 1: Exponential Growth
In the beginning, the population
grows slowly. After a short time,
the population grows exponentially.
Resources are unlimited,
so individuals grow and reproduce
rapidly. Population becomes larger
and larger.

29. Phases of Growth:
Phase 2: Growth Slows Down As a result of limiting factors,
the growth of the population
begins to slow down. The
population size increases
more slowly.

31. Phases of Growth: Phase 3: Growth Stops The population stops growing,
the population will remain at or
near this size. The population
reaches its carrying capacity.

33. Logistic Growth (S-shape)
Growth slows.
Carrying
capacity
Growth
stops.
Population
grows rapidly.

34. Carrying capacity is the maximum number of individuals of a particular species that a particular environment can support.
1000 bison is the
carrying capacity
of this preserve.
1000
Carrying
capacity

35. What determines the carrying capacity of an area?
1000 bison is the
carrying capacity
of this preserve.
1000
Limiting factors
determines the
carrying capacity
of an environment
for a species.

36. When populations are under the carrying capacity, births exceed deaths and the population grows until the carrying capacity is reached.
If the population grows beyond the carrying capacity, deaths exceed births and the population decreases to below the carrying capacity.
Number of Organisms
Time (yrs)

37. Growth of a Sheep Population
Population overshoots carrying capacity
Environmental resistance
2.0
Carrying capacity
1.5
Population recovers and stabilizes
Number of sheep (millions)
Population runs out of resources and crashes
1.0
Exponential growth
Animated Figure 5.16 Growth of a sheep population on the island of Tasmania between 1800 and After sheep were introduced in 1800, their population grew exponentially thanks to an ample food supply and few predators. By 1855, they had overshot the land’s carrying capacity. Their numbers then stabilized and fluctuated around a carrying capacity of about 1.6 million sheep. .5
1800
1825
1850
1875
1900
1925
Year
Fig. 5-16, p. 115

38. the number of individuals in the population.
Density-dependent factor- Any factor limiting the size of a population whose effect is dependent on
the number of individuals in the population.
Examples:
food, disease, parasites, predation, and competition

39. Density-independent factors control population growth regardless of the population's density.
Example:
fire, flood, hurricane, severe freeze, habitat destruction

40. How do communities and ecosystems respond to changing environmental conditions?
The structure and species composition of communities and ecosystems change in response to changing environmental conditions through a process called ecological succession.

41. Mount St Helen, WA
(before 1980)

42. Mount St Helen, WA
(May 18, 1980)

43. One of the most violent natural disasters of our time, the colossal eruption of Mt. St. Helens in 1980 blasted away an entire mountainside. Over 200 square miles of pristine forest were buried under millions of tons of lava, ash, mud, and avalanche debris. How could life ever return to this barren moonscape? 
May 1980

45. Today

46. Communities and Ecosystems Change over Time: Succession
Gradual change in species composition in an area
Two types of succession:
Primary succession
Secondary succession

47. - occurs in lifeless area….no soil…no life
Primary succession
- occurs in lifeless area….no soil…no life
Examples – bare rock, lava flow, new volcanic island,
land exposed after retreating glacier, an abandoned parking lot.

49. - occurs in lifeless area….no soil…no life
Primary succession
- occurs in lifeless area….no soil…no life
A series of changes occurs over tens to hundred of years
….as different organisms inhabit the area
Break down
rock
making soil

50. - occurs in lifeless area….no soil…no life
Primary succession
- occurs in lifeless area….no soil…no life
Break down
rock
making soil

51. Perennial weeds and grasses
Secondary succession
Occurs in an area where the natural community has been disturbed or destroyed, but the soil remains.
Clear-cut forest, burned forest,
flooded land, hurricane
Mature oak
and
hickory forest
Young pine forest
with developing understory of oak
and hickory trees
Shrubs
and
small pine seedlings
Perennial weeds and grasses
Annual weeds
Time
Fig. 5-12, p. 110

52. Perennial weeds and grasses
Secondary succession
Occurs in an area where the natural community has been disturbed or destroyed, but the soil remains.
Clear-cut forest, burned forest,
flooded land, hurricane
Mature oak
and
hickory forest
Young pine forest
with developing understory of oak
and hickory trees
Shrubs
and
small pine seedlings
Perennial weeds and grasses
Annual weeds
Time
Fig. 5-12, p. 110