1. Bellringer
Last class we discussed different interspecific relationships, can you label the following as:
Parasitism
Mutualism
Commensalism

2. 5.3: What Limits the Growth of Populations
POPULATION ECOLOGY
No population can grow indefinitely because of limitations on resources and because of competition among species for those resources

3. Population Ecology

4. Most Populations Live in Clumps
Group of interbreeding individuals of the same species
Population distribution
Clumping
Species cluster for resources
Protection from predators
Ability to hunt in packs

5. Types of Distribution

6. Populations Can Grow, Shrink, or Remain Stable
Populations density
Number of individuals in a given area
Population size governed by:
Births and deaths;
immigration and emigration
Population change = (births + immigration) – (deaths + emigration)

7. Population Change
(births + immigration) – (deaths + emigration)

8. Different Species Have Different Reproductive Strategies (r-K)
Some species:
Have many small offspring
Little parental involvement
Other species:
Reproduce later in life
Have small number of offspring

9. Survivorship Curves A survivorship curve
Shows expected mortality (death) rates of members of a population over their potential life span.
Survivorship curves can be classified into three general types
Type I, Type II, and Type III

10. Survivorship Curve 1,000 I Number of survivors (log scale) II 10 III 150
100 1 10
1,000
Percentage of maximum life span
Number of survivors (log scale)
Figure 52.5

11. Survivorship Curves

12. Populations Can Grow, Shrink, or Remain Stable
Age structure
Pre-reproductive age
Reproductive age
Post-reproductive age

13. Some Factors Can Limit Population Size
No population can grow indefinitely because of limitations on resources and because of competition among species for those resources…
Range of tolerance
Variations in physical and chemical environment
Individuals may have different tolerance ranges

14. Zone of physiological stress Zone of physiological stress
Trout Tolerance of Temperature
Lower limit
of tolerance
Higher limit
of tolerance
No organisms
Few organisms
Few organisms
No organisms
Abundance of organisms
Population size
Figure 5.15 Range of tolerance for a population of trout to changes in water temperature.
Zone of intolerance
Zone of physiological stress
Zone of physiological stress
Zone of intolerance
Optimum range
Low
Temperature
High
Fig. 5-13, p. 113

15. Some Factors Can Limit Population Size
Limiting factor principle
Too much or too little of any physical or chemical factor can limit or prevent growth of a population, even if all other factors are at or near the optimal range of tolerance
Precipitation, nutrients, sunlight

16. No Population Can Grow Indefinitely: Carrying Capacity
There are always limits to population growth in nature
Environmental resistance – factors that limit population growth
Carrying capacity (K)
Maximum population of a given species that a particular habitat can sustain indefinitely

17. No Population Can Grow Indefinitely: J-Curves and S-Curves
Exponential growth
At a fixed percentage per year
Logistic growth
Population faces environmental resistance

18. Growth of a Sheep Population
Population overshoots carrying capacity
Environmental resistance
2.0
Carrying capacity
1.5
Population recovers and stabilizes
Number of sheep (millions)
Population runs out of resources and crashes
1.0
Exponential growth
Animated Figure 5.16 Growth of a sheep population on the island of Tasmania between 1800 and After sheep were introduced in 1800, their population grew exponentially thanks to an ample food supply and few predators. By 1855, they had overshot the land’s carrying capacity. Their numbers then stabilized and fluctuated around a carrying capacity of about 1.6 million sheep. .5
1800
1825
1850
1875
1900
1925
Year
Fig. 5-16, p. 115

19. When a Population Exceeds Its Carrying Capacity It Can Crash
A population exceeds the area’s carrying capacity
Reproductive time lag may lead to overshoot
Subsequent population crash
Damage may reduce area’s carrying capacity

20. Population Cycles for the Snowshoe Hare and Canada Lynx
Figure 5.18: This graph represents the population cycles for the snowshoe hare and the Canadian lynx. At one time, scientists believed these curves provided evidence that these predator and prey populations regulated one another. More recent research suggests that the periodic swings in the hare population are caused by a combination of top-down population control—through predation by lynx and other predators—and bottom-up population control, in which changes in the availability of the food supply for hares help to determine their population size, which in turn helps to determine the lynx population size. (Data from D. A. MacLulich)
Fig. 5-18, p. 118

21. Humans Are Not Exempt

22. Human Impact

23. Ecological Footprint The ecological footprint concept
land and water area needed to sustain the people of a nation
Is one measure of how close we are to the carrying capacity of Earth

24. Activity GROUP A Using computer, calculate your ecological footprint
GROUP B Work on population growth POGIL