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

2. Key Questions How do populations change in size, density, and makeup?
What is the role of predators in controlling population size?
What is conservation biology?
How can we live more sustainably?

3. Major Characteristics of a Population
Populations can change in…
Size (number of individuals)
Density (number of individuals in a certain area)
Dispersion (spatial pattern)
Age distribution

4. Dispersion Clumped (elephants) Uniform (creosote bush) Random
(dandelions)

5. These changes are called…
Population Dynamics!
-occur in response to environmental stress OR changes in environmental conditions

6. What Limits Population Growth?
Births
Deaths
Immigration (to a new area)
Emigration (out of an area)
Population change = (births + immigration) – (deaths + emigration)

7. Populations Populations vary in biotic potential (growth)
Intrinsic rate of increase (r)-rate at which a population would grow if it had unlimited resources

8. High intrinsic rate of increase populations…
Reproduce early in life
Short generation times
Reproduce many times
Many offspring each time they reproduce

9. Example… FLIES!-high intrinsic rate of increase/biotic potential
Without control, there would be 5.6 trillion flies within 13 months
Within a few years, flies could cover the surface of the earth!

10. Of course…
This is not realistic because no population can grow indefinitely
There are always limiting factors!

11. Environmental Resistance
all limiting factors
together the biotic potential and environmental resistance determine the carrying capacity

12. (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
© 2004 Brooks/Cole – Thomson Learning
Population Size

13. A Few More Terms
Carrying Capacity (K)-number of individuals that can be sustained in a given space
Minimum viable population (MVP)-minimum population size needed to support a breeding population (below MVP, extinction is likely)

14. Exponential and Logistic Growth
A population has exponential growth when it has few/no resource limitations (J-shaped curve)
Logistic growth- exponential population growth that approaches carrying capacity and levels off (S-shaped curve)

15. © 2004 Brooks/Cole – Thomson Learning
Population size (N)
Population size (N)
Time (t)
Time (t)
Exponential Growth
Logistic Growth

16. What Happens If Population Size Exceeds Carrying Capacity?
Overshoot-exceeds carrying capacity
Dieback-happens unless individuals change resources or move to another area
Humans are not exempt from this!
Potato fungus in Ireland; 1 million died/3 million emigrated

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

18. How Does Density Affect Population Growth?
Density-independent population controls (do NOT depend on size of population): floods, fires, hurricanes, habitat destruction, pesticides
Density-dependent population controls (depend on size of population): competition, predation, disease, parasitism

19. Population Curves in Nature
Stable: fluctuates slightly above and below carrying capacity (undisturbed areas)
Irruptive: fairly stable with occasional explosions
Irregular: chaotic, no recurring pattern
Cyclic: regular cycles

20. Natural Population Curves

21. Do Predators Control Population Size?
YES!
Lynx-Hare Cycle:
Shortage of hares reduces lynx population
Hare population builds up because there are fewer predators
Lynx population increases because there are more hares
Cycle begins again

22. Two Ideas About Lynx-Hare Cycle
Top-down control hypothesis: lynx controls hare population
Bottom-up control hypothesis: hare controls lynx population

23. Population size (thousands)
160
140
Hare
120
100
Lynx
Population size (thousands) 80 60 40 20
Year

24. Reproductive Patterns and Survival
Asexual reproduction: all offspring are exact copies (clones) of a single parent
Sexual reproduction: combination of gametes (97% of species)
r-selected species
K-selected species

25. Reproductive Patterns
r-selected: opportunist species; high intrinsic rate of increase; reproduce early; algae, bacteria, rodents, insects
Many offspring each time they reproduce
Reproduce at young age
Short generation times
Little or no parental care
Short life-spans
Irregular and unstable changes in population size

26. Little or no parental care and protection of offspring
r-Selected Species
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

27. Reproductive Patterns, continued
K-selected: competitor species; mammals, long-lived plants, birds of prey
Reproduce late in life
Few offspring
Long generation times
Nurture and protect their young
Logistic growth curve

28. Fewer, larger offspring High parental care and protection of offspring
K-Selected Species
elephant
saguaro
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

29. Figure 9-9 Page 196 Time Number of individuals Carrying capacity K
K species;
experience
K selection
Number of individuals
r species;
experience
r selection
Time

30. Survivorship Curves
Shows the number of survivors of each age group for a species
3 Types:
1. Late Loss Curves: high survivorship to a certain age, then high death rate (elephants, humans)
2. Constant Loss Curves: constant death rate at all ages (songbirds)
3. Early Loss Curves: survivorship is low early in life (r-selected species)

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

32. Conservation Biology Started in the 1970s
Uses science to take action to preserve species and ecosystems
3 principles
Biodiversity is necessary to all life on earth and should not be reduced by humans
Humans should not disrupt vital ecological processes
The best way to preserve earth’s biodiversity is to protect ecosystems