1. Characteristics of a Population
1. Geographical Distribution 2. Density 3. Growth Rate

2. 1. Geographical Distribution
area inhabited by a population
could be as small as a few cubic centimeters like a bacteria or as large as millions of kilometers like killer whales

3. 2. Population Density the number of individuals per unit
How organisms are dispersed can be important
Three patterns of dispersal are random, clumped, and uniform

4. 3. Growth Rate 3 factors that affect a population size
- number of births
- number of deaths
- number of individuals entering and leaving a population
A population will increase or decrease in size depending on the number added or removed from it

5. 3. Growth Rate A population will grow if: Birth Rate > Death Rate
(# of individuals born) (# of individuals who die)
A population will stay the same if: Birth Rate = Death Rate
A population will decline if: Birth Rate < Death Rate

6. Emigration – Exit (out)
3. Growth Rate
Individuals entering and leaving the population will also increase or decrease a population’s size
- Immigration: movement of individuals into an area (increase population)
- Emigration: movement of individuals out of an area (decrease population)
Remember….
Immigration – Into
Emigration – Exit (out)

7. Population Growth Initial growth- birth (natality) is high1 2 3 4 5
Initial growth- birth (natality) is high
Exponential growth
Carrying capacity- steady state
Decline- increase in death rate
Extinction

8. Exponential Growth
If a population has abundant space and food, protection from predators and disease then the organisms in the population will multiply and the population will increase. Under ideal conditions with plenty of nutrients, heat, moisture, & light a bacteria can reproduce by splitting in half within 20 minutes producing 2 bacteria.
In 20 minutes the population is 2
In 40 minutes the population is 4
In 1 hour: the population is 8
In 2 hours: 64
In 3 hours: 512
In one day: 4,720,000,000,000,000,000,000
The pattern of growth is a J-shaped curve and the population is undergoing exponential growth
Exponential growth occurs when the individuals in a population reproduce at a constant rate

9. Exponential Growth = J-curve
At first, the number of individuals increases slowly, over time the population becomes larger and larger until it approaches an infinitely large size.
1 million
Exponential Growth =
J-curve
Population size
500,000
100
One year
Under ideal conditions with unlimited resources, a population will grow exponentially

10. ExponentialLogistic Growth
Exponential growth doesn’t continue in natural populations for very long
If a new species of organism is introduced into a new environment, at first the population grows slowly, then exponentially, eventually the population growth slows down (the size has not dropped, but the population is growing slower).

11. Logistic Growth Logistic Growth = S-curve
As resources become less available, the growth of a population slows or stops forming an S-shaped curve- logistic growth
Birth rate decreases and death rate increases
Logistic Growth =
S-curve

12. Carrying Capacity When growth levels off The population is not growing
Carrying capacity- the largest number of individuals that an environment can support
When a population overshoots the carrying capacity, then limiting factors may come into effect
A balance between environmental factors must exist for a population to survive
For example:
- Producers = consumers
- Water use = Rainfall

13. Population Growth Logistic Exponential growth Limits on S-shaped curve
can be
represented by
characterized by
which cause a
Exponential
growth
Logistic
Falling
growth rate
S-shaped
curve
Limits on
No limits on
J-shaped
Constant
Unlimited
resources

14. Limiting Factors Any factor that causes population growth to decrease
Limiting factors, such as availability of food, disease, predators, or lack of space, will cause population growth to slow
Under these pressures, the population may stabilize in an S-shaped growth curve

15. Characteristics of Population Growth
J curve
S curve
Carrying capacity
Exponential growth
Time
Population
DISEASE
SPACE
PREDA-TORS
FOOD

16. Density-Dependent Limiting Factors
A limiting factor that depends on population size is a density-dependent limiting factor.
Density-dependent factors include
competition
predation
parasitism
disease
Disease, for example, can spread more quickly in a population with members that live close together.
Density dependent factors create an S-shaped curve
Population sizes are limited not only by abiotic factors, but also are controlled by various interactions among organisms that share a community.

19. Competition Competition is a density-dependent factor
When only a few individuals compete for resources, no problem arises
When a population increases to the point at which demand for resources exceeds the supply, the population size decreases
Competition can also occur between members of different species- this creates evolutionary change
The two species competing are under stress to change in way that decrease competition- eventually evolving to occupy separate niches

20. Predation Predation is a density-dependent factor
When a predator consumes prey on a large enough scale, it can have a drastic effect on the size of the prey population
Populations of predators and their prey are known to experience cycles or changes in their numbers over periods of time

21. Parasitism and Disease
Parasites can also limit a population’s size (density-dependent)
As the # of individuals , parasites which then causes the # of individuals to
Parasites are similar to a predator in that they take nourishment at the expense of their host
As a population increases in size, disease is more common because individuals are in closer contact with one another

22. Parasitism and Disease

23. Density-Independent Limiting Factors
Density-independent factors can affect all populations, regardless of their size
Most density-independent factors are abiotic factors, such as temperature, storms, floods, drought, and major habitat disruption

24. Density-Independent Factors
Density-independent factors create a boom-and bust curve (exponential growth followed by a sudden collapse)
Examples:
Weather- a drought kills grass
Human activity: deforestation- destroys habitat
Seasons: a severe winter regulates insect population

25. Boom-and-Bust Curve
Time
Population Density

26. Limitations on Population Growth

27. Human Population Growth
Industrial
Revolution
begins
Agriculture
begins
Bubonic
plague
Plowing
and
irrigation
Until about 500 years ago, the population grew slowly. Agriculture and industry made life easier and safer.

28. Human Population We are growing exponentially
Due to technological advances: medicines, a dependable food supply, and sanitation
The death rate is decreasing and the life expectancy is increasing
The human population will eventually reach its carrying capacity

29. Human Impact on the Environment
Environmental resources can be classified into two types:
Renewable
Can regenerate (replaceable)
Nonrenewable
Cannot be replenished by natural processes
Example: Fossils fuels (formed over hundreds of millions of years)
Sustainable Use
Way of using natural resources at a rate that does not deplete them.
Renewable resources affected:
Land, air, and water

30. Human Impact: Land Deforestation
The loss of forests which leading to severe erosion and changes in soil properties
Erosion
The wearing away of surface soil by water and wind
Desertification
The combination of farming, overgrazing, and drought in dry climates which turn productive areas into deserts
Deforestation erosion water pollution and desertification

31. Human Impact: Air Greenhouse effect Acid Rain
Trapping of heat by gases in the Earth’s atmosphere (carbon dioxide)
This may lead to global warming- increase in the Earth’s temperature from the rapid buildup of carbon dioxide and other greenhouse gases
Acid Rain
Burning of fossil fuels release nitrogen and sulfur into the atmosphere which combined with water form nitric and sulfuric acid
Acid Rain kills plants
Smog
Mix of chemicals in the air from automobile exhaust
Affects the respiratory system especially those with asthma

32. The Formation of Acid Rain
Section 6-2
Chemical Transformation
Nitric acid
Sulfuric acid
Condensation
Emissions to Atmosphere
Nitrogen oxides
Sulfur dioxide
Dry Fallout
Precipitation
Acid rain, fog,
snow, and mist
particulates, gases
Industry
Transportation
Ore smelting
Power generation

33. Human Impact: Water
Nutrients can cause an increase in algae growth and depletion of oxygen for other organisms
Over harvesting of fish has reduced the number of fish
Although water is a renewable resource, the total supply of fresh water is limited

34. Humans need to learn to be a part of nature not apart from nature!
Consequences
If humans continue to alter the environment, they will have to deal with the results
Examples: fossil fuels combustion, habitat destruction, deforestation, ozone layer destruction, global warming
Human Overpopulation results in:
Worldwide malnutrition
Increased disease
Increased pollution
Humans need to learn to be a part of nature not apart from nature!

35. Biodiversity is one of the world’s greatest resources
Biological Diversity
Biodiversity: the sum total of the genetically based variety of all organisms in the biosphere
Ecosystem diversity- variety of habitats, communities, and ecological processes in the living world
Species diversity- the number of different species
Genetic diversity- sum total of all the different forms of genetic information carried by all organisms living on Earth today
Biodiversity increases as you move toward the equator.
Areas around the world differ in biodiversity
Biodiversity can bring stability to an ecosystem.
Biodiversity is one of the world’s greatest resources

36. Loss of Biodiversity
Extinction is the disappearance of a species when the last of its members dies.
Extinction is a natural process and Earth has experienced several mass extinctions during its history.
A species is considered to be an endangered species when its numbers become so low that extinction is possible

37. Threats to Biodiversity
Complex interactions among species make each ecosystem unique. Changes to habitats can therefore threaten organisms with extinction
Human activity can reduce biodiversity by altering habitats, hunting species to extinction, introducing toxic substances into food webs, and introducing invasive species
Habitat loss-One of the biggest reasons for decline in biodiversity

38. Threats to Biodiversity: Biological Magnification
Fish-Eating Birds
Threats to Biodiversity: Biological Magnification
Magnification of
DDT Concentration
10,000,000
Increasing concentrations of a harmful substance in organisms at higher trophic levels in a food chain or web
Example: DDT
Large
Fish
1,000,000
Small Fish
100,000
Zooplankton
10,000
1000
Producers 1
Water

39. Threats to Biodiversity: Introduced Species
Introduced species threaten biodiversity
Introduced species are organisms that have been introduced into new habitats and often become invasive, reproduce rapidly
Invasive species lack density-dependent limiting factors to keep their populations in check and take over areas and out compete existing species
Native to South America, nutrias have become pests in coastal areas of the US. These furry rodents eat water plants that protect fragile shorelines from erosion. This destroys the habitats of species native to those ecosystems.