1. POPULATION ECOLOGY

2. Density and Dispersion
Density - The number of individuals per unit area
What are the three patterns of dispersion?

3. Patterns of Dispersion Within a Population’s Geographic Range
Clumped
Random
Uniform

4. Estimating Population Size
Mark re-capture method.
You capture 200 grasshoppers, mark them all and then release them back into the wild. A few days later you capture 100 grasshoppers and 50 of them were marked. How many grasshoppers do you estimate are in this population?

5. N = # marked x # recaptured
number marked & recaptured
200 x 100/50 = 400
Original Population is approx. 400

6. You capture 50 rabbits, mark all them
and release them back into the wild.
The following week you capture 30
rabbits and 15 are marked. How many
rabbits do you estimate in the population?

7. 50 rabbits marked X 30 recaptured
15 marked recaptured
Original Population is approx 100.

8. Demography Study of vital statistics that affect population size
Life Tables are age-specific summaries of the survival pattern of a population

9. Life Table for Belding Ground Squirrels (Spermophilus beldini) at Tioga Pass, in the Sierra Nevada Mountains of California

10. Age Structure – the relative number
of individuals at each age commonly
represented in pyramids. It shows
present and future growth trends.

11. Age Structure Pyramids

12. Survivorship Curves
Plot of the numbers of a cohort that are alive at each age.
Survivorship curves are generally classified into three types:

13. Survivorship Curves

14. Life Histories
Traits that affect time of reproduction and death including:
1. Clutch size
2. Number of reproductive episodes per lifetime
3. Age at first reproduction

15. Species that exhibit semelparity, or “big-bang” reproduction
reproduce
once and die
Figure 52.6

16. Species that exhibit iteroparity, or repeated reproduction
Produce offspring repeatedly over time

17. Birds with high probability of dying have larger clutch sizes

18. Large clutch sizes mean one reproductive episode per life.
Small clutch sizes means more than one reproductive episode
Age at first reproduction is younger in large clutch size reproducers; they invest less energy in their own growth and development.

19. Models of Population Growth
r = reproductive rate, r = b-d/N
b = births, d = deaths, N = population size
multiply both sides of the equation by N, we get: rN = b-d , rN = change in population during a given time interval: DN/ Dt = b - d

20. Models of Population Growth
r max = the maximum rate of increase in growth of a species; intrinsic/maximum rate of increase
The equation for exponential population growth is: dN/ dt = rmaxN

21. r max = 1
r max = .5

22. Population Density is the number of individuals per unit area.
Three factors affect a population’s size:
number of births
number of deaths
number of individuals who immigrate
and emigrate

23. Exponential Growth occurs when
the individuals in a population
reproduce at a constant rate. At
first, the number of individuals in
an exponentially growing
population increases slowly,
but over time the population
becomes larger and larger.
(J shaped curve)

24. Logistic Growth occurs when a
population’s growth slows or stops following a period of exponential growth. (S shaped curve)

25. Exponential
Growth Curve
Carrying Capacity
Logistic Growth
Curve

26. The logistic growth equation
Includes K, the carrying capacity, the largest number of individuals of a population that an environment can support dN dt 
(K  N) K
rmax N

27. Table 52.3

28. If N is less than K, then the population growth is positive and population increases?
What is occurring here?

29. Are all examples of logistic growth?

30. What sort of limiting factor is seen here?

31. Density Dependent Selection

32. A limiting factor causes
population growth to decrease.

33. Density Dependent Factors
become limiting only when the
per unit area –
reaches a certain level
Examples: competition,
predation, parasitism, and
disease.

34. Density Independent Factors
affect all populations in similar
ways, regardless of the population
size.
Examples include unusual
weather,
natural disasters, seasonal cycles,
and certain human activities (such
as damming rivers or cutting
forests)

35. What sort of limiting factor is seen
here?

36. Density Independent Selection

37. K selection (density dependent
long maturation time
long lifespan
low death rate
few offspring/reproduction
several reproductive episodes
reproduces later in life
large sized offspring
parental care for young

38. r selection (density independent selection)
short maturation time
short life-span
high death rate
many offspring/reproduction
one reproductive event
reproduces early in life
small sized offspring
no parental care

39. Usually more than 1 limiting factor is at work

40. Describe the population shifts seen below:

41. Are we at carrying capacity?