1. Chapter 53
Population Ecology

2. You Must Know:
How density, dispersion, and demographics can describe a population.
The differences between exponential and logistic models of population growth.
How density-dependent and density- independent factors can control population growth.

3. Introduction Density: _____________________
Population = group of individuals of a single species living in same general area
Density: _____________________
Dispersion: pattern of ___________ ___________________ individuals

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

5. Patterns of Dispersal:
_________________ – most common; near required resource
________________ – usually antagonistic interactions
___________________ – unpredictable spacing, not common in nature

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

7. ______________________________: represent # individuals alive at each age
Type I: ______ death rate early in life (______________)
Type II: ______________ death rate over lifespan (squirrels)
Type III: ________ death rate early in life (___________)

8. Reproductive strategies
___________________________
__________ reproduction
____________ offspring
invest a lot in raising offspring
primates
coconut
__________________
_______ reproduction
_________ offspring
little parental care
insects
many plants
K-selected
r-selected

9. “Of course, long before you mature, most of you will be eaten.”
Trade offs
___________________of offspring
vs.
____________ of offspring or parent
r-selected
K-selected
“Of course, long before you mature, most of you will be eaten.”

10. Life strategies & survivorship curves25
1000
100
Human
(type I)
Hydra
(type II)
Oyster
(type III) 10 1 50
Percent of maximum life span 75
Survival per thousand
K-selection
A Type I curve is flat at the start, reflecting low death rates during early and middle life, then drops steeply as death rates increase among older age groups. Humans and many other large mammals that produce few offspring but provide them with good care often exhibit this kind of curve. In contrast, a Type III curve drops sharply at the start, reflecting very high death rates for the young, but then flattens out as death rates decline for those few individuals that have survived to a certain critical age. This type of curve is usually associated with organisms that produce very large numbers of offspring but provide little or no care, such as long–lived plants, many fishes, and marine invertebrates. An oyster, for example, may release millions of eggs, but most offspring die as larvae from predation or other causes. Those few that survive long enough to attach to a suitable substrate and begin growing a hard shell will probably survive for a relatively long time. Type II curves are intermediate, with a constant death rate over the organism’s life span. This kind of survivorship occurs in Belding’s ground squirrels and some other rodents, various invertebrates, some lizards, and some annual plants.
r-selection

11. Change in Population Size
t = time
Change in population size during time interval
Births during time interval
Deaths during time interval = -

12. Factors that limit population growth:
Density-Dependent factors: population density matters
i.e. _______________, _______________, _______________, territoriality, waste accumulation, physiological factors
Density-Independent factors: population density not a factor
i.e. _______________,: fire, flood, __________

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

14. What do you notice about the population cycles of the showshoe hare and lynx?

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

16. Introduced species _______________________ species kudzu
transplanted populations grow ___________________ in new area
__________________ native species
loss of natural controls
lack of __________________, parasites, ____________________________
reduce ______________________
examples
African honeybee
gypsy moth
zebra mussel
purple loosestrife
gypsy moth
kudzu

17. Population Growth Models

18. Exponential population growth: ____________ conditions, population grows ______________

19. Exponential growth rate
Characteristic of populations without _________________________________
introduced to a new environment or rebounding from a catastrophe
Whooping crane
coming back from near extinction
African elephant
protected from hunting
The J–shaped curve of exponential growth is characteristic of some populations that are introduced into a new or unfilled environment or whose numbers have been drastically reduced by a catastrophic event and are rebounding. The graph illustrates the exponential population growth that occurred in the population of elephants in Kruger National Park, South Africa, after they were protected from hunting. After approximately 60 years of exponential growth, the large number of elephants had caused enough damage to the park vegetation that a collapse in the elephant food supply was likely, leading to an end to population growth through starvation. To protect other species and the park ecosystem before that happened, park managers began limiting the elephant population by using birth control and exporting elephants to other countries.

20. Exponential Growth Equation
dN/dt = change in population
r = growth rate of pop.
N = population size

21. 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?

22. Logistic rate of growth
Can populations continue to grow exponentially?
Of course not!
no natural controls
K = carrying capacity
Decrease rate of growth as N reaches K
effect of natural controls
What happens as N approaches K?

23. _____________________________
Time (years)
1915
1925
1935
1945 10 8 6 4 2
Number of breeding male
fur seals (thousands)
Maximum population size that environment can _____________ with no degradation of habitat
varies with changes in resources
500
400
300
200
100 20 10 30 50 40 60
Time (days)
Number of cladocerans
(per 200 ml)
What’s going on with the plankton?

24. Changes in Carrying Capacity
Population cycles
predator – prey interactions
At what population level is the carrying capacity? K K

25. Unlimited resources are rare
Logistic model: incorporates carrying capacity (K)
_____ = maximum stable population which can be sustained by environment

26. Logistic Growth Equation
dN/dt = change in population
r = growth rate of pop.
N = population size
K = carrying capacity

27. Logistic Growth Problem
Sample Problem:
If a population has a carrying capacity (K) of 900, and the growth rate (r) is 1.1, what is the population growth when the population (N) is 425?

28. 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

29. Semelparity Big-bang reproduction ___________________ produced at once
Individual often dies afterwards
__________ stable environments
Agave Plant

30. Iteroparity Repeated reproduction _____________________ offspring
More ______________ environments
Lizard
Critical factors: survival rate of offspring and repeated reproduction when resources are limited

31. K-selection r-selection
K-selection: pop. close to carrying capacity
r-selection: maximize reproductive success
K-selection
r-selection
Live around K
____________ growth
High ___________ care
Little or no _______
_____ birth numbers
______ birth numbers
______ survival of young
Density _____________
ie. ______________
ie. _____________

32. Zero Population Growth

33. Human Population Growth
2 configurations for a stable human population (zero population growth):
High birth / high death
Low birth / low death
________________________________: occurs when population goes from __  __

34. Age-Structure Diagrams

35. Global Carrying Capacity
Current world population (2015) = 7.3 billion
Estimated carrying capacity = billion?
_________________________________: 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?