1. Chp 46 - Ecology of Populations

2. Scope of Ecology Ecology
The study of the interactions of organisms with:
Other organisms and the physical environment

3. Ecological Levels
Population - All the individuals of a species within a particular space
Community – Specified populations interacting with each other
Ecosystem - Community interacting with environment
Organism – a single individual

4. Density and Distribution of Populations
Population Density - Number of individuals per unit area or volume
State
Population
Area
(Sq. Mi.)
Population Density
California
36,756,666
155,959
Alaska
686,293
571,951
New York
19,490,297
47,214
Texas
24,326,974
261,797
Montana
967,440
145,552

5. Density and Distribution of Populations
Population Density - Number of individuals per unit area or volume
State
Population
Area
(Sq. Mi.)
Population Density
California
36,756,666
155,959
235.68
Alaska
686,293
571,951
1.20
New York
19,490,297
47,214
412.81
Texas
24,326,974
261,797
92.92
Montana
967,440
145,552
6.65

6. Density and Distribution of Populations
Population Distribution - Pattern of dispersal of individuals within a space of interest
Ecologists analyze what causes the spatial and temporal “patchiness” of organisms

7. Population’s Distribution
Clumped
Random
Uniform

8. Density and Distribution of Populations
Resources – abiotic & biotic components of the environment that support living organisms.
Availability influences distribution
Limiting factors - are factors that predominantly determine whether a species lives in a habitat
Trout – cool streams; high O2 content
Timberline – trees cannot grow above

9. Estimating Population Size
Mark re-capture method
N = MC
Where…
N = Estimate of total population size
M = Total number of animals captured and marked on the first visit
C = Total number of animals captured on the second visit
R = Number of animals captured on the first visit that were then recaptured on the second visit R

10. Estimating Population Size
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?

11. N = # marked x # recaptured number marked & recaptured
Estimating Population Size
N = # marked x # recaptured
number marked & recaptured
200 x 100/50 = 400
Population is approximately 400

12. Estimating Population Size
You capture 50 rabbits, mark all them & 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?

13. 50 rabbits marked X 30 recaptured Original Population is approx 100.
Estimating Population Size
50 rabbits marked X 30 recaptured
15 marked recaptured
Original Population is approx 100.

14. Population Growth Rate of Natural Increase (Growth Rate) Depends upon:
Birth Rate & Death Rate
Ex. 30 born & 10 die for every 1,000 in the population.
(30-10)/1,000 = .02 or 2%

15. Population Growth
Biotic Potential - Maximum population growth that can possibly occur under ideal circumstances.
Depends on:
Usual # of offspring/reproductive event
Chances of survival until age of reproduction
How often each individuals
Age at which reproduction begins

16. Population Growth High Biotic Potential
Pigs produce many offspring that mature quickly to produce more offspring…
High Biotic Potential

17. Population Growth Low Biotic Potential
Rhinoceroses produce only one or two offspring for each infrequent reproductive event…
Low Biotic Potential

18. Mortality Patterns Cohort Survivorship
Composed of all the members of a population born at the same time
Survivorship
The probability that newborn individuals of a cohort will survive to a particular age

19. Survivorship Curves
Type I – Most individuals live past midpoint of life (ex. Large mammals & humans)
Type III – most individuals die very young (ex. Inverts, fish & humans in less developed countries)
Type II – Survivorship decreases at a constant rate & death is unrelated to age (ex. Songbirds & small mammals)

20. Survivorship Curves

21. Age Distributions There are 3 major Groups Prereproductive ages
Postreproductive ages

22. Exponential Growth Exponential growth
occurs when the individuals in a population reproduce at a constant rate. (r > 0)
At first, the number of individuals in an exponentially growing population increases slowly, but over time the population becomes larger and larger.

23. Exponential Growth (J shaped curve) 2 phases: Lag Phase
Exponential Growth Phase
Figure 46.7b

24. Exponential Growth
Figure 46.7a

25. Exponential Growth
Figure 46.7c

26. Logistic Growth Logistic growth
Occurs when environmental resistance retards exponential growth (r = 0)
Growing populations must eventually come under the control of environmental resistance

27. Logistic Growth
Figure 46.8b
S – shaped Curve

28. Logistic Growth
Figure 46.8a

29. Logistic Growth

30. Logistic Growth Carrying Capacity
The maximum # of individuals of a given species that the environment can support. (r = 0)
The closer the population to the carrying capacity, the greater the environmental resistance
“K” represents the carrying capacity of the environment.

31. Carrying Capacity Carrying Capacity Exponential Growth Curve
Logistic Growth
Curve

32. Sample Population Problem #1
A population of 1000 has a 60 births & 10 deaths over a 1-year period. What is the reproductive (growth) rate? Does this show exponential or logistic growth patterns?

33. Sample Population Problem #1
r = (60-10)/1,000 or 0.05 per year

34. Sample Population Problem #2
In 2009 the U.S. had a population of about 307 million. If there are 14 birth & 8 deaths per 1,000 people (ignoring immigration & emigration) what was the countries net population growth?

35. Sample Population Problem #2
r = (14-8)/1,000 = 0.006/year * 307,000,000 = 1.84 million

36. Regulation of Population Size
Density-independent Factors
Density-dependent Factors

37. Regulation of Population Size
Density-independent Factors
Number of organisms present does not influence the effect of the factor
Natural disasters
Mortality Rate
3/5=0.6 or 60%
Mortality Rate
12/20=0.64 or 64%

38. Regulation of Population Size
Density-dependent Factors
Number of organisms present influences the effect of the factor
Competition
Predation

39. Regulation of Population Size
Density-dependent Factors
Low Population Density High Population Density

40. Regulation of Population Size
Density-dependent Factors

41. Life History Patterns r - Strategists (Opportunistic)
Produce large numbers of offspring
Small body size
Early maturity
No parental care
Controlled by density-independent factors
Good dispersers and colonizers

42. r - Strategists (Opportunistic)
Life History Patterns
r - Strategists (Opportunistic)

43. Life History Patterns k - Strategists (Equilibrium)
Produce small numbers of offspring
Large body size
Late maturity
Significant parental care
Controlled by density-dependent factors
Specialists

44. k - Strategists (Equilibrium)
Life History Patterns
k - Strategists (Equilibrium)

45. Human Population Growth
Human population has an exponential growth pattern
Doubling time currently estimated at 53 years
Population Size
1800 = 1 Billion
1930 = 2 Billion
1960 = 3 Billion
2000 = 6 Billion

46. Country Development More-Developed Countries (MDCs)
Slow population growth
High standard of living
Completed Demographic Transition
North America and Europe

47. Country Development Less-Developed Countries (LDCs)
Rapid population growth
Low standard of living
Latin America
Africa and Asia

48. Environmental Impact
Environmental impact of a population is measured in terms of:
Population size
Resultant pollution
Resource consumption per capita