1. Populations

2. Bell Ringer
A nearby high school is closing, and all their students will be coming to your high school. What will be different about your school with the addition of all these new students?

3. Growing Populations
Increases in general populations can put stresses on resources
Which resources do we protect and consume?
Abundance or scarcity of food sources?
Disruption of ecological systems?

4. Florida School Project
What does the problem at Central High have to do with the environment?
Do you think it is important to protect the gopher tortoise?
What are some ways that building the school will affect the gopher tortoise?
Do you think any living organisms were affected when (your school) was built?

5. What are gopher tortoises?

6. Gopher Tortoise
Keystone species - alter the habitat by constructing and maintaining their burrows
Indicator species - used as an indicator of ecosystem health.

7. Burrow Details Protect from temperature extremes and predators
Max. length 13 m (40 feet), depth 3m (10 feet)
Burrow has ledge at end where tortoise rests

8. Population Ecology
A population is a group of members of the same species defined by geographic boundaries
Population dynamics help ecologists understand how a population may grow or decline.

9. Population Dynamics Size - # of organisms
Density - # of individuals with a population per unit area
High population density = easier for organisms to find mates, may lead to conflict in competing for resources
Low population density = organisms benefit from space & resources, difficult to locate mates.

10. Population Distribution/Dispersion
Spatial arrangement of organisms within an area.
Random = no pattern.
Uniform = Evenly spaced
Clumped = In groups

11. Sex Ratios – Proportion of males to females
Age Structure – relative numbers of organisms of each age within a population
Pre-reproductive
Reproductive
Post-reproductive

12. Age Pyramids
Visual tools used to show the age structure

13. What limits population growth?
Births
Deaths
Immigration
Emigration
Population change = (b + i) – (d + e)

14. Survivorship Graphs

15. Identify biotic/abiotic factors that limit population size
Growth Factors
Decrease Factors
Abiotic Factors
Biotic Factors

16. High reproductive rate Adequate food supply Suitable habitat
POPULATION SIZE
Growth factors
Decrease factors
Abiotic
Abiotic
Favorable light
Favorable temperature
Favorable chemical environment
(optimal level of critical nutrients)
Too much or too little light
Temperature too high or too low
Unfavorable chemical environment
(too much or too little of critical
nutrients)
Biotic
Biotic
High reproductive rate
Adequate food supply
Suitable habitat
Ability to compete for resources
Ability to hide from or defend
against predators
Ability to resist diseases and parasites
Low reproductive rate
Inadequate food supply
Unsuitable or destroyed habitat
Too many competitors
Insufficient ability to hide from or defend
against predators
Inability to resist diseases and parasites

17. Populations (r) = growth rate
Population change = (b + i) – (d + e)
2 models of population growth:
1) Exponential growth: assumes ‘r’ stays constant
2) Logistic growth: as popns grow, resources diminish

18. Exponential population growth
Under ideal conditions, a population grows rapidly
(J-shaped curve)

19. Logistic Population Growth
Unlimited resources are rare, so populations tend to level out.
S-shaped curve

20. 3 Phases in Logistic Growth
Carrying Capacity
The maximum stable population size a particular environment can support
Occurs when Birth rate = Death rate

21. Bell Ringer Describe the 2 models of population growth.
What is carrying capacity?
Identify factors that can limit carrying capacity factors.

22. Carrying Capacity Limited by density-dependent factors
Competition for limited resources (food, water, territory)
Health (overcrowded plants produce less seeds)
Physiological factors (overcrowding in field mice causes stress)

23. 2 Types of Life Histories Strategies
K-strategists: organisms live and reproduce around K, and are sensitive to population density
R-strategists: organisms exhibit high rates of reproduction and live in unstable environments in which population densities fluctuate

24. 2 Types of Life Histories Strategies
K Selected - Equilibrial
R Selected - Opportunistic
Long life span
Long maturation time
Low death rate
Few offspring
Several reproductions per lifetime
Extensive parental care
Usually in stable, predictable environments
Good competitors
Ex: tigers, whales, elephants
Short lifespan
Short maturation time
High death rate
Usually one reproduction/lifetime
Many offspring
No parental care
Temporary large populations followed by crashes
Unpredictable changing environments
Ex: insects, bacteria

25. Humans: R or K?
From beginning to 1350 AD, humans experienced logistic growth
But agriculture (food surplus), medicine, and technology expanded carrying capacity
Eventually, damage to planet will decrease carrying capacity and slow human growth leading to environmental, health, food & social changes.

26. Human Population Growth