1. Population Ecology

2. Introduction
Population = group of individuals of a single species living in same general area
Density: # individuals / area
Dispersion: pattern of spacing between individuals

3. Determining population size and density:
Count every individual
Random sampling
Mark-recapture method

4. Patterns of Dispersal:
Clumped – most common; near required resource
Uniform – usually antagonistic interactions
Random – unpredictable spacing, not common in nature

5. Demography: the study of vital statistics that affect population size
Additions occur through birth, and subtractions occur through death.
Life table : age-specific summary of the survival pattern of a population

6. Survivorship Curve: represent # individuals alive at each age
Type I: low death rate early in life (humans)
Type II: constant death rate over lifespan (squirrels)
Type III: high death rate early in life (oysters)

7. POPULATION PROBLEMS

8. NO … not that problem … these problems

9. Components needed know
B = number of births
I = number of immingrants
D = number of deaths
E = number of emmigrants
b = birth rate
d = death rate
N = population size
r = population growth rate

10. Change in Population Size
dN/dt = B-D
t = time
Change in population size during time interval
Births during time interval
Deaths during time interval = -

11. Calculate population growth rate (r)
With emigration and immigration
r = (B + I) – (D +E) N0
Without emigration and immigration
r = B – D = b - d

12. Zero Population Growth …

13. Population Growth Models

14. Exponential population growth: ideal conditions, population grows rapidly

15. Exponential Growth Equation

16. Exponential Growth Problem
Sample Problem:
A certain population of mice is growing exponentially. The growth rate of the population (r) is 1.3 and the current population size (N) is 2,500 individuals. How many mice are added to the population each year?

17. Calculating Population of Next Generation(s) … Exponential Growth
N1 = N0r + N0 ... repeat until you reach generation of choice Or
Nt = N0 ( r)t ... Where subscript and superscripts = time

18. Doubling Time – only applies to exponential growth
When r is in % form, 70% r When r is in decimal form, 0.7

19. What is the current population density of Transylvania?
SAMPLE PROBLEM: The country of Transylvania contains 2.3 million people (not including vampires) and covers 800,000 square miles. In the year after that last census, there were 111,000 new children born and 109,000 people died.
What is the current population density of Transylvania?
What is the population growth rate (r)?
What will be the population of Transylvania in 25 years?
What is the doubling time of Transylvania?
Density = 2.9 people/mi2
r = = 0.087%
N25 = 2,350,551
doubling time = 805 years

20. Logistic Model
Unlimited resources are rare
Incorporates carrying capacity (K)
= maximum stable population which can be sustained by environment

21. Logistic Growth Equation
dN/dt = change in population

22. Calculation of next generation population size - Logistic Growth
N1 = N0 + r N0[(K- N0)/K]

23. Logistic Growth Problem
Sample Problem:
If a population has a carrying capacity (K) of 900, and the growth rate (r) is 1.1, what will be the population size in generation 1 when the population (N0) is 425?
672

24. Life History: traits that affect an organism’s schedule of reproduction and survival
3 Variables:
Age of sexual maturation
How often organism reproduces
# offspring during each event
Note: These traits are evolutionary outcomes, not conscious decisions by organisms

25. Semelparity Big-bang reproduction Many offspring produced at once
Individual often dies afterwards
Less stable environments
Agave Plant

26. Iteroparity Repeated reproduction Few, but large offspring
More stable environments
Lizard
Critical factors: survival rate of offspring and repeated reproduction when resources are limited

27. K-selection r-selection
K-selection: pop. close to carrying capacity
r-selection: maximize reproductive success
K-selection
r-selection
Live around K
Exponential growth
High prenatal care
Little or no care
Low birth numbers
High birth numbers
Good survival of young
Poor survival of young
Density-dependent
Density independent
ie. Humans
ie. cockroaches

28. Factors that limit population growth:
Density-Dependent factors: population matters
i.e. Predation, disease, competition, territoriality, waste accumulation, physiological factors
Density-Independent factors: population not a factor
i.e. Natural disasters: fire, flood, weather

29. Biotic & abiotic factors  Population fluctuations
: peak in wolf numbers
1995: harsh winter weather (deep snow)

30. Boom-and-bust cycles Predator-prey interactions
What do you notice about the lynx and snow hare relationship?

31. Boom-and-bust cycles Predator-prey interactions
Eg. lynx and snowshoe hare on 10-year cycle

32. Human Population Growth
Age-Structure Diagrams

34. Global Carrying Capacity
Current world population =
Estimated carrying capacity = billion?
Ecological footprint: total land + water area needed for all the resources a person consumes in a pop.
1.7 hectares (ha)/person is sustainable
Typical person in U.S. = 10 ha footprint
Limitations? Consequences? Solutions?

36. Map of ecological footprint of countries in the world (proportional sizes shown)