1. Population Dynamics, Carrying Capacity and Conservation Biology
CHAPTER 9
Population Dynamics, Carrying Capacity and Conservation Biology

2. A. Characteristics of a population
I. Population Dynamics
A. Characteristics of a population
1. Size - number of individuals
2. Density - number of individuals per space
3. Age Distribution – portions of individuals of each age

3. 4. Dispersion – spatial patterns of organisms

4. B. Factors that govern population size
Immigration
Births
Deaths
Emigration

5. C. Terms Related to Populations
1. Zero Population Growth
Lost = Gains
2. Biotic Potential
Populations Capacity for growth

6. 3. Intrinsic Rate of Increase (r)
Rate at which a population would grow with unlimited resources
Populations with a high “r”…
Reproduce early in life
Short generation times
Can reproduce many times
Have many offspring each time they reproduce

7. 4. Environmental Resistance
All factors acting jointly to limit the growth of a population
Together biotic potential and environmental resistance determine…

8. 5. Carrying Capacity “k”
-Number of individuals of a given species that can be sustained in a given space indefinitely

9. 6. Minimum Viable Population (MVP)
Fewest number of members of a species needed to insure the species survives
If a population declines below MVP…
- Certain individuals may not be able to find a mate
-Interbreeding occurs (weak or mutant offspring)
-Genetic diversity may be too low to adapt to environmental changes

10. D. Estimating Carrying Capacity
Best done using an ecological footprint
“The total area of productive land and water required on a continuous basis to produce the resources consumed, and to assimilate the wastes produced, by that population, wherever on Earth the land (and water) is located”

11. Six Types of Productive Areas Used to Calculate Ecological Footprint
*Arable land *Ocean
*Pasture *Built-up Land
*Forest *Fossil Energy Land
All converted to Hectares
(1 ha = 2.47 acres)
About 2 ha per person on planet
(1.7 if use land for parks)

12. *U.S. has footprint of 8.4 ha/person but only 6.2 ha/person available
*Counties vary greatly in their individual footprint size and ecological capacity.
*U.S. has footprint of 8.4 ha/person but only 6.2 ha/person available
*Overall analysis suggests world is over carrying capacity.
U.S.
World

13. II. POPULATION GROWTH Growth occurs in two ways… A. Exponential:
Population with few or no resource limitations.
Starts slow and increases
“J-shaped curve”
Population size (N)
Time (t)

15. Slowing as the population encounters environmental resistance
B. Logistic:
Exponential at first…
Slowing as the population encounters environmental resistance
“S- shaped curve” K
Population size (N)
Time (t)

16. Number of sheep (millions)
2.0
1.5
1.0 .5
Number of sheep (millions)
1800
1825
1850
1875
1900
1925

18. What if Population Size Exceeds “k”
-A population may use up resources and overshoot the “k”
-Overshoot occurs due to…
Reproductive Lag Time
Period needed for the birth rate to fall and the death rate to rise in response to overconsumption

19. - This lag can cause Dieback or Crash
-Occurs unless the excess individuals…
Switch to new resources
Move to an area with more favorable conditions

20. Reindeer in Alaska 2,000 1,500 Number of reindeer 1,000 500 1910 1920
1930
1940
1950
Fig. 9.6, p. 201
Year

21. -Potato Famine -Ireland (1845)
Humans are not exempt from carrying capacity diebacks and crashes…
-Easter Island
-Potato Famine
-Ireland (1845)

22. SHOW VIDEO http://www.youtube.com/watch?v=-hO-vCPuuQQ

23. The earth’s carrying capacity has been extended by…

24. III. Factors that Affect Carrying Capacity
Competition
Immigration and Emigration
Catastrophic Events
Seasonal Fluctuations

25. (environmental resistance)
POPULATION SIZE
Growth factors
(biotic potential)
Favorable light
Favorable temperature
Favorable chemical environment
(optimal level of critical nutrients)
Abiotic
Biotic
High reproductive rate
Generalized niche
Adequate food supply
Suitable habitat
Ability to compete for resources
Ability to hide from or defend
against predators
Ability to resist diseases and parasites
Ability to migrate and live in other
habitats
Ability to adapt to environmental
change
Decrease factors
(environmental resistance)
Too much or too little light
Temperature too high or too low
Unfavorable chemical environment
(too much or too little of critical
nutrients)
Low reproductive rate
Specialized niche
Inadequate food supply
Unsuitable or destroyed habitat
Too many competitors
Insufficient ability to hide from or defend
Inability to resist diseases and parasites
Inability to migrate and live in other
Inability to adapt to environmental

26. IV. Population Limiting Factors
A. Density-Independent Controls:
Affect a population size regardless of the density
Flood, hurricanes, drought, fire, habitat destruction, pesticide spraying

27. B. Density-Dependent Controls:
Greater effect as density increases
Competition, predation, parasitism and disease

28. C. Natural Population Curves
1. Stable:
Fluctuates slightly above and below the “k”
2. Irruptive:
Population explodes and crashes back to a lower level
3. Irregular:
Changes irregularly for unknown reasons
4. Cyclic:
Sharp increases followed by crashes in a regular pattern

29. Time Number of individuals 3. Irregular 1. Stable 4. Cyclic
2. Irruptive
1. Stable
4. Cyclic
3. Irregular

30. V. Predation and Population Control
1. Top-Down Hypothesis
-Possible explanation for the 10-year population cycles of Hare and Lynx
-Lynx preying on hares reduce their population
-Shortage of hares reduces the lynx population
-Lower # of Lynxes, hares increase
-Lynx pop. Increases due to greater food supply

32. 2. Bottom-Up Control *Second possible reason for hare decline
Based on study where hare numbers decreased on island w/o lynx members
Believed that population crashes may be a result of decreases in primary producers

33. Population size (thousands)
The Lynx-Hare Cycle
Population size (thousands)
160
140
120
100 80 60 40 20
1845
1855
1865
1875
1885
1895
1905
1915
1925
1935
Year
Hare
Lynx

34. VI. REPRODUCTION AND SURVIVAL
A. Types of reproduction:
-Asexual:
Creates a genetic clone
Common in simple organism
-Sexual:
Create offspring by union of gametes
Costly/risky to organisms
Done by 97% of known organisms

35. B. Reproduction Patterns
1. Opportunists: (r-selected species)
-Reproduce early and put most of their energy into it
-Large litters
-Reach reproductive age early
-Short generation times Little or no care to the offspring
-Reproduce quickly when a disturbance opens up a new niche
-Often get displaced by a more competitive species

36. r-Selected Species Many small offspring
cockroach
dandelion
Many small offspring
Little or no parental care and protection of
offspring
Early reproductive age
Most offspring die before reaching
reproductive age
Small adults
Adapted to unstable climate and environmental
conditions
High population growth rate (r)
Population size fluctuates wildly above and below
carrying capacity (K)
Generalist niche
Low ability to compete
Early successional species

37. 2. Competitor or (k-Selected Species)
-Put little energy into reproduction
-Reproduce late in life
-Few offspring
-Long generations
-Put energy into protection and nurturing
-Display long growth
-Thrive best in constant environments
*Availability of habitat determines the population size

38. Fewer, larger offspring High parental care and protection of offspring
Later reproductive age
Most offspring survive to reproductive age
Larger adults
Adapted to stable climate and environmental
conditions
Lower population growth rate (r)
Population size fairly stable and usually close
to carrying capacity (K)
Specialist niche
High ability to compete
Late successional species
elephant
saguaro
K-Selected Species

39. C. Survivorship Curves
Shows the number of survivors at each age group of a particular species
Late Loss:
k-selected species, reduced juvenile mortality
Ex: Humans and elephants
Early Loss:
r-selected species, high juvenile mortality
Constant Loss:
face mortality at all ages
Songbirds, lizards, small mammals

40. Percentage surviving (log scale)
100 10 1
Age

42. VII. CONSERVATION BIOLOGY
Sustaining wildlife populations
Goals:
Investigate human impacts on biodiversity
Develop practical approaches to maintain biodiversity
Key Topics:
Endangered species management
Wildlife reserves
Ecological Restoration
Ecological Economics
Environmental Ethics

43. 3 Principles of Conservation Biology
Biodiversity is necessary to all life and should not be reduced by human actions
Humans should not hasten extinction
The best way to preserve biodiversity is to protect intact ecosystems and provide habitat