1. Population Control

2. Populations Population
Group of interbreeding individuals of the same species
Population Dynamics = Changes in populations (demography)
Can change in size, density dispersion or age distribution
Population Ecology = number of individuals of a species in an area AND how/why the number changed over time.
Effected by
Resource competition
Predation
Disease

3. Population Size Number too small Number too large
Better chance of extinction
Too much inbreeding
Can’t adapt (not enough genetic diversity)
Number too large
Starvation
Increased predation
Decreased fertility
Parasitism & disease are likely

4. Population Density Number at a certain time in certain space
Ecological population density = individuals per unit of habitat
Area for terrestrial
Volume for aquatic

5. Population Density Population Density = # of individuals
area or volume
Determined by external factors
Habitat
Resources
What is the population density of 200 birds in 20 square miles?
A: 200/20 = 10

6. Most Populations Live in Clumps
Population distribution
Clumping
Species cluster for resources/better chance of finding resources
Protection from predators (allows some predators to get prey)
Ability to hunt in packs
Social

7. Most Populations Live in Clumps
Uniformly dispersed
Rare pattern
Resources may be scarce-defend resources by physical/chemical means
Randomly dispersed
Resources evenly spread out
Fairly rare

8. Populations Can Grow, Shrink, or Remain Stable
Population size governed by:
Births and immigration (b and i)
Deaths and emigration (d and e)
Population change = (births + immigration) – (deaths + emigration)
Age structure
Pre-reproductive age
Reproductive age
Post-reproductive age

9. Some Factors Can Limit Population Size
Density dependent vs density independent factors
Range of tolerance
Variations in physical and chemical environment
Individuals may have different tolerance ranges
Trout
tolerance of
temperature

10. 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

11. What Limits the Growth of Populations
No population can grow indefinitely because of limitations on resources and because of competition among species for those resources
Change in response to environmental stress or change in environmental conditions
Growth rate (r)
r = (b-d) + (i-e)
If r (+), population size
If r (-), population size
If r = 0, stationary population size

12. No Population Can Grow Indefinitely: J-Curves and S-Curves
Biotic or reproductive potential (r)
Maximum rate at which a population can grow if it has unlimited resources!
High potential if:
Reproduce early in life
Has short generation times
Can reproduce many times
Produce many offspring each time
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

13. No Population Can Grow Indefinitely: J-Curves and S-Curves
“r” + environmental resistance = “k”
Populations can exceed their carrying capacity
When this happens
The corrective negative feedback loop does not take effect immediately
A dieback (population crash) results

14. No Population Can Grow Indefinitely: J-Curves and S-Curves
Exponential growth
When populations are growing at biotic potential
At a fixed percentage per year
Logistic growth
Population faces environmental resistance

15. When a Population Exceeds Its Carrying Capacity It Can Crash
A population exceeds the area’s carrying capacity
Members will die unless they adapt or move to another area with more resources
Reproductive time lag may lead to overshoot
Subsequent population crash
Damage may reduce area’s carrying capacity

16. Minimum Viable Population (MVP)
Estimate of smallest # of individuals necessary to ensure the survival of a population
If below MVP = extinction likely
Individuals can’t find mates
Genetically related individuals breed = weak or malformed offspring
Genetic diversity = too low

17. Case Study: Exploding White-Tailed Deer Population in the U.S.
1900 – deer habitat destruction and uncontrolled hunting
1920s–1930s – laws to protect the deer
Current deer population explosion
Spread Lyme disease
Deer-vehicle accidents
Eating garden plants and shrubs

18. Different Species Have Different Reproductive Patterns
“r-strategists”
Life based on r (growth rate)
Rapidly increase numbers
Below carrying capacities for long periods of time
“k-strategists”
Life based on carrying capacity (k)
Live in a state of equilibrium
Close to carrying capacity

19. Reproductive Strategies: “r-strategists”
Live in disturbed environments
Generalists
Have populations that fluctuate rapidly in size
Do not compete well with other species
Are widely distributed
Slow to respond to ecological opportunities but live in a wide variety of environments
Short-lived
Have many relatively small young
Have short periods of embryonic development
Reach adulthood rapidly
Small sized adults
Invest little or no parental care in young
Reproduce once per lifetime
Go through regular boom and bust cycles

20. Reproductive Strategies “k-strategists”
Live in stable environments
Specialists
Have populations stable in size
Compete well against other species
Restricted in distribution and where they can live
Take advantages of ecological opportunities but live in specific types of environments
Are long-lived
Have few, relatively large young
Have long periods of embryonic development
Reach adulthood slowly
Large sized adults
Invest intensive parental care in young
Reproduce throughout lifetime
Do well when population size is near “k”

21. Survivorship Curves
Many organisms have reproductive patterns between the extremes of “r” & “k”
Some change from one to the other depending on environment
R-strategists: early loss
K-strategists: late loss
In between = constant loss

22. Humans Are Not Exempt from Nature’s Population Controls
Ireland
Potato crop in 1845
Bubonic plague
Fourteenth century
AIDS
Current global epidemic