1. Chapter 52
Population Ecology

2. Population Ecology Study of
Populations in relation to their environment.
Environmental influences on
Pop. Density
Distribution
Age structure
size

3. Population:
Individuals of a single species that occupy the same general area.

4. Important Characteristics
Density
2. Dispersion

5. Density Number of individuals per unit area or volume. Ex:
Diatoms - 5 million/m3
Trees - 5,000/km2
Deer - 4/km2

6. Dispersion
The pattern of spacing among individuals within the boundary of the population.

7. How do you count a population?
1. actual count
2. Random plots, then extrapolate
3. Indirect indicators: number of nests; burrows; tracks; droppings
4. MARK & RECAPTURE METHOD

8. Mark and Recapture Method N= Population estimate
Trap, capture, mark, release.
Later-recapture, determine proportion of those recaptured that were marked.
N= # marked in first catch X Total # in 2nd catch
Number of marked recaptures
Assumptions:
1. the proportion of marked animals in the 2nd trapping is equivalent to the proportion of marked animals in the total population
2. Those marked mix uniformly within the pop.

9. Population densities not static
Birth
Death
Immigration
Emmigration

10. Dispersal patterns
3 general patterns
Know these!!

12. 1. Clumped Pattern Most common pattern
Results form patchy environmental conditions-food, nutrient availability.
Ex: Mushrooms under rotting log.
Groups enhance predation
Safety. May increase chances for survival.
Ex:
Schooling behavior
Flocks of birds
humans

14. 2. Uniform Dispersion Individuals are evenly spaced
Results from direct antagonistic interactions
Plants secrete chemicals-inhibit nearby germination & competition (alleopathy)
territoriality

16. 3. Random Dispersion Spacing varies unpredictably
Absence of strong attractions or repulsions between individuals.
RARE pattern in nature
Example: windblown seeds land randomly & germinate.

18. Demography
Study of vital statistics of a population & how they change over time.
Add
Lose
2 most important features
Age structure-relative numbers of individuals of each age group in a population
Sex ratios

19. 1. Life Tables
How long, on average, are individuals of a given age expected to live.
Age-specific summary of survival patterns.
Follow the fate of a cohort (indiv. Of same age) from birth to death.

20. Do males or females have a higher death rate? Who lives longer?

21. 2. Survivorship Curves Graphic representation of data in Life Tables.
Plot of the proportion or numbers in a cohort still alive at each age.
3 general Curve Types: ( be able to recognize and describe traits; members exhibiting each; example organism)
Type I—humans, elephants
Type II-squirrel
Type III-oysters, clam

22. Draw and label in your notes

23. Type I
Low early deaths.
Steep decline in death rates among those older
Produce few offspring, but provide good care.
Ex:
Humans
Other large mammals

24. Constant death rate over life span.
Type II
Intermediate
Constant death rate over life span.
Ex:
Annual plants
small mammals ( grey squirrel), lizards

25. Type III High death rates for the young. Few live to adulthood
( sharp dip in curve initially)
Few live to adulthood
Associated with:
Produce large numbers of offspring-but provide little or no care.
Ex: Oysters

26. Variations Curve type may change between young and adults.
Ex: Nestlings - Type III Adult Birds- Type II
Stair-step curve
Invertebrates—crabs; high mortality during molt, followed by low mortality

27. Life-History Traits Life History: Timing of reproduction and death.
Highly diverse, but do show patterns
Determines how populations grow.
Results from Natural Selection.
Darwinian “fitness”

28. Darwinian “fitness”
Survive AND Reproduce

29. Reproduction and survival—Life History Traits
1. # of reproductive episodes
# offspring per reproductive episode
Age at first reproduction

30. 2 Common Reproductive Patterns
1. Semelparity: “big-bang” reproduction
1 reproduction event
Salmon, agave ( desert plants) , annual plants
2. Iteroparity
Fewer offspring at a time
Over many reproductive seasons

31. Population Studies & Reproductive Rates
Focusing on females and female offspring.
2 Kinds of Reproductive Strategies identified R K

32. Life History Selection
1. "r" Selected species
2. "k" Selected species

33. “r" – Selected Species (density independent selection)
Increase fitness by producing as many offspring as possible.
Do this by one of these strategies:
Early maturation
Many reproductive events
Many offspring in one reproductive event
“Big bang” reproduction (semelparity) (pink salmon, agaves) is one time reproduction.

34. r-Selected Result
Maximize reproduction so that at least a few offspring survive to the next generation.
Most offspring die (Type III curve).

35. “K" – Selected Species (density dependent selection)
Increase fitness by having most offspring survive.
Maintain populations at or near “K”
Do this by:
High parental care
Late maturation
Few reproduction events
Few offspring.

36. K- Selected –Results.. Maximize survivorship of each offspring .
Few offspring, but most survive (Type I curve).

37. What is the strategy
For a weed?
For Garden Pests?

38. POULATION GOWTH Zero population growth:
Per capita birth + Per capita death=0

39. Exponential Growth Produces a “J-shaped” growth curve.
Ideal conditions
unlimited resources.
Example:
Introduce into new or unfilled environment
Rebounding population

40. Logistic Growth-

41. Logistic Growth-S curve
K = carrying capacity
The rate of population growth slows as the population reaches K. of the environment.
Limiting factor influence
S-shaped (sigmoid) curve

42. Population growth related to Life History Traits
S-shaped” growth curve.
Characteristic of “k" species.
Common when resources are limited.

45. Populations are limited by space, food
Populations are limited by space, food. That limit is called the CARRYING CAPACITY
The graph shows a logistic population curve.
At what level do the deer reach their CARRYING CAPACITY?

46. What Limits Population Size?
Density-dependent factors: limited resources- space, food, water, air
related to population size
Density-independent factors: random occurrences that can limit population - earthquake, bad weather.
not affected by population size
Is disease density dependent, or density independent?

47. Additional Comments
Populations often overshoot “K” ( go beyond) , then drop back to or below “K”.

48. Regular Population Cycles
Cyclic changes in N over time.
Often seen in predator/prey cycles.
Ex: “Boom & Bust Cycle” of Snowshoe
Hare -& Lynx

49. Why predators rarely kill and eat all the prey:
Predators kill and consume other organisms. Carnivores prey on animals, herbivores consume plants.
Predators usually limit the prey population, although in extreme cases they can drive the prey to extinction.
Why predators rarely kill and eat all the prey:
1.Prey species often evolve protective mechanisms such as camouflage, poisons, spines, or large size to deter predation.
2.Prey species often have refuges where the predators cannot reach them.
3.Switch its prey as the prey species becomes lower in abundance:

51. Know how to read a graph for population growth, where K is; where the overshoot “K” is

53. Age Structure Diagrams
Show the percent of a population in different age categories .
Method to get data similar to a Life Table, but at one point in time.

55. HUMAN POPULATION GROWTH
Grown since history
1A.D. 300 million
Since 1650 ( 500 million), growing exponentionally.
Over 6 billion today

56. Exponential Growth
Produces age structures that are a triangle or pyramid shape.

57. Logistic Growth
Produces age structures that have even sizes between most age categories.

58. Declining Populations
Produce age structures with a narrow base and wider middles.

59. Reveal current and future growth trends.

61. Ecological Footprint Model to predict “K”
Relative to The Available Ecologic capacity
Land usage requirements to meet our varied human needs.

62. Summary Know density and dispersion patterns.
Know Life Tables and survivorship curves ( and representative organism for the 3 types).
Know what “K” is
Be able to contrast and compare “r” and “k” strategies ( Suggest making a chart-include Logistic Curve, Exponential growth curve, characteristics of populations).
When/how density independent, and dependent growth factors affect pop size.
Know how (match) Age-structure pyramids relate to either Rapid, Slow, or Zero Pop. Growth; their shapes & what the shape means.

63. Summary
Know exponential and logistic growth curves.Relate them to PGR