1. Populations & Limits on Growth
Ch. 5

2. APES
Turn in:
Salinity Lab
Predator/Prey Lab
Peppered Moth

3. Populations
Group of similar individuals/species

4. Population Distribution
Clumped
(elephants)
(b) Uniform
(creosote bush)
(c) Random
(dandelions)

5. Why Clumping? Species tend to cluster where resources are available
Groups have a better chance of finding resources
Protects some animals from predators
Packs allow some predators to get prey

6. How do populations change over time?
Population Ecology  # of individuals of a species in an area AND how/why those # change over time
Effected by:
Resource competition
Predation
disease

7. Population Density
# of individuals Area or volume Determined by external factors (habitat/resources) What is the population density of 200 birds in
Population Density

8. Population Density
What is the population density of 200 birds in 20 square miles?
What about 200 birds in 5 square miles?
Which area is more densely populated?

9. Limits on Population Growth
Population Increase (+)
Population Decrease (-)
Births (b)
Immigration (i)
Death (d)
Emmigration (e)

10. Growth Rate (r) (also termed rate of change)
r = b - d
If r (+), population size
If r (-), population size
If r (0), b=d, stationary population size

11. Therefore…
True growth rate includes b, d, i, e
r = (b-d)+(i-e)

12. How do populations change over time?
Ideally, population would according to biotic potential

13. Biotic Potential
Maximum rate at which a population can increase when there are no limits on its rate of growth

14. Biotic Potential is Influenced by:
Reproduction age
Reproductive periods
# of offspring
Care of offspring

15. GENERALLY… Organisms with a high biotic potential:
Reproduce early in life
Have short generation times
Can reproduce many times
Have many offspring each time they reproduce

16. GENERALLY… Small organisms have large biotic potential
EX: Housefly – descendants = 5.6 trillion in 13 mo.
Bacteria dividing in ½ every 30 min.
Ancestors of Female housefly could be 5.6 trillion flies within 13 months – just a few years cover earth’s surface

17. Exponential Growth
Results when organisms are growing at biotic potential
Population size (N)
Time (t)
Exponential Growth

18. NO POPULATION CAN GROW INDEFINATELY!

19. Environmental Resistance
All factors acting jointly to limit the growth of a population
Population size determined by:
Biotic potential
Environmental resistance

20. Environmental Resistance
Unfavorable environmental conditions due to resource availability As environmental conditions deteriorate, b and d

21. Carrying Capacity (K)
Largest population that can be maintained given fixed resources
- S (sigmoid) shaped curve (logistic Growth)
Carrying capacity K
Reflects influence of Env. Resistance
Populations rarely stays at K
If it rises above K, pop will crash
Population size (N)
Time (t)

24. What Happens When Populations Exceed Carrying Capacity
Members of populations which exceed their resources will die unless they adapt or move to an area with more resources.

25. Population Cycles for the Snowshoe Hare and Canada Lynx
Figure 5.18: This graph represents the population cycles for the snowshoe hare and the Canadian lynx. At one time, scientists believed these curves provided evidence that these predator and prey populations regulated one another. More recent research suggests that the periodic swings in the hare population are caused by a combination of top-down population control—through predation by lynx and other predators—and bottom-up population control, in which changes in the availability of the food supply for hares help to determine their population size, which in turn helps to determine the lynx population size. (Data from D. A. MacLulich)
Fig. 5-18, p. 118

26. Minimum Viable Population (MVP)
Estimate of smallest # of individuals necessary to ensure the survival of a population
Red wolf – extinct 1980
Reintroduced in N.E. NC – Alligator river – genetically mixed with Coyote and gray wolf, but considered different species

27. Below MVP Extinction = Likely Individuals can’t find mates
Genetically related individuals breed = weak or malformed offspring
Genetic diversity = too low

28. Species Have Different Reproductive Patterns
Asexual reproduction
Sexual reproduction
All species engage in struggle for genetic immortality by trying to have as many memberes of the next generation as possible carry their genes
Costs/Risks/Benefits of sexual reproduction- see notes

29. Reproductive Strategies
r-strategists
k-strategists
Life based on r (growth rate -r)
Rapidly increase numbers
Below carrying capacities for long periods of time
Life based on carrying capacity (k)
Live in a state of equilibrium
Close to carrying capacity

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

31. r strategists (based on study)
+ Live in disturbed environments.
+ Ecological generalists.
+ Have populations that fluctuate rapidly in size.
+ Do not compete well against other species
+ Are widely distributed.
+ Are slow to respond to ecological opportunities but live in wide varieties of environments.
+ Are short-lived.
+ Have many, relatively small young.
+ Have short periods of embryonic development.
+ Reach adulthood rapidly
+ Small sized adults.
+ Invest little or no parental care in young.
+ Reproduce once per lifetime.
+ Early successional species.

32. r-selected species Once established – population crash because
Changing environment
Invasion by more competitive species
Go through regular BOOM and bust cycles

33. k strategists (based on study)
+ Live in stable environments.
+ Ecological specialists.
+ Have populations stable in size.
+ Compete well against other species.
+ Are restricted in distribution and where they can live.
+ Take rapid advantage of ecological opportunities but live in specific types of environments.
+ Are long-lived.
+ Have few, relatively large young.
+ Have long periods of embryonic development.
+ Reach adulthood slowly.
+ Large sized adults.
+ Invest intensive parental care in young.
+ Reproduce throughout lifetime
+ Late successional species.

34. K-selected species
Do well when pop. size is near K Typically follow logistic growth Thrive in constant environment

35. Many organisms have reproductive patterns between the extremes of r & K, or change from one to the other depending on environment*

36. Percentage surviving (log scale)
Survivorship Curves
Percentage surviving (log scale)
100 10 1
Age

37. Reproductive strategy may give temporary advantage BUT the availability of suitable habitat determines ultimate population size

38. Factors Affecting Population Growth/Population Density
Density Independent Limiting Factors
Density Dependent Limiting Factors
Floods
Fires
Hurricanes
Unseasonable Weather
Habitat Destruction
Competition
Predation
Parasitism
Disease

39. Zone of physiological stress Zone of physiological stress
Range of Tolerance
Lower limit
of tolerance
Higher limit
of tolerance
No organisms
Few organisms
Few organisms
No organisms
Abundance of organisms
Population size
Figure 5.13: This diagram illustrates the range of tolerance for a population of organisms, such as trout, to a physical environmental factor—in this case, water temperature. Range of tolerance restrictions prevent particular species from taking over an ecosystem by keeping their population size in check. Question: For humans, what is an example of a range of tolerance for a physical environmental factor?
Zone of intolerance
Zone of physiological stress
Zone of physiological stress
Zone of intolerance
Optimum range
Low
Temperature
High
Fig. 5-13, p. 113