Unit 3 Human Population and Carrying Capacity

1. Unit 3 Human Population and Carrying Capacity

2. Population Dynamics • is the study of how populations change in size, density and age distribution. • Size- total number of individuals • Density- number of individuals in a certain space( spatial distribution) • Age distribution- the proportion of individuals of each age in a population

3. Four Factors affecting Population size?How do populations increase or decrease?

4. Immigration: movement of individuals of a species into a country or an area • Emigration: movement of individuals of a species out of a country or area

5. Natality – birthrate • Mortality- deathrate

6. Population Change=(Natality+Immigration)-(Mortality+Emigration

7. Exponential Growth • A population with few or no resource limitations grows exponentially. • Rate 1% - 2% • Examine the data: starts slowly and gradually increases • Invasive species • Whooping crane p.169

8. However, this is not true for most populations. • Together biotic potential(essentially how fast they can reproduce without the environment having an impact) and environmental resistance (environmental limits that affect population growth) determine a carrying capacity for a population. • Carrying capacity (K) - the maximum population of a particular species that a given habitat can support.

9. Fig. 9-4

10. Logistic Growth • involves rapid exponential growth followed by a steady decline in population growth until the population size levels off. • This occurs because the population encounters environmental resistance and its rate of growth decreases as it approaches the carrying capacity. • After leveling off, the population fluctuates slightly above and below the carrying capacity.

11. Overshoot- when organisms use up their resources and temporarily exceed their carrying capacity • This happens because of a reproductive time lag: the period needed for the birthrate to drop and the deathrate to rise as a result of resource overconsumption. Fig. 9-6 Fig. 9-5

12. A dieback or crash occurs unless a switch to an alternate resources or leaves the area. • Reindeer introduced on an island in Alaska had no alternate resource and the death of the herd. Fig. 9-6

13. What limits population growth? • Limiting Factor -when a particular condition or factor can be identified as a key component that limits the size of a population. • Air, water, nutrients, food, shelter, etc. • There are four categories of limiting factors:

14. 1. Availability of Raw Materials • Plants need nitrogen and magnesium from the soil as raw materials to manufacture chlorophyll. • Adding fertilizer to the soil is a way of preventing nitrogen from being a limiting factor.

15. 2. Availability of Energy Plants require energy from sunlight. Animals require food energy. Food webs can be changed.

16. 3. Accumulation of Waste Products • commonly a limiting factor for bacteria and organisms that live in small ecosystems such as puddles, pools and petri dishes. • not a limiting factor for most organisms

17. 4. Interactions among Organisms • Since cottontail rabbits and white tailed deer eat the twigs of many species of small trees, they have a limiting effect on the size of some tree populations. • Parasites and predators cause the premature death of individuals thus limiting the size of the populations.

18. Factors Affecting Population Size Fig. 9-3

19. Types of Population Change curves • stable-fluctuates above and below the carrying capacity • irruptive-a stable population which on occasion will explode or irrupt • cyclic-cyclical fluctuations over a defined period of time • irregular-no order the fluctuations- chaos

20. Natural Population Curves Fig. 9-7

21. Where Might the human population be on this growth curve?

23. Human population • Video clip : http://www.youtube.com/watch?v=4BbkQiQyaYc

24. See worksheet: Applying Human Populations