1. Human Population Growth Impacts
Tragedy of the Commons
Loss of Biodiversity by:
Altering habitats
Hunting species to extinction
Introduction of toxic compounds into the food webs
Introduced foreign species
How else does the growing population negatively affect the environment?

2. Tragedy of the Commons
Once upon a time… a few hundred years ago, inhabitants of English villages could graze their cattle on shared pasture land called commons.
Idea that any resource accessible to everyone, may eventually be destroyed.
Why do you think this is so?
For example: Water is available to everyone, but one day it may be destroyed by people.
Every once in a while there were more cattle taken to the commons than the land could support. Even as the land became overused and overgrazed people continued to put their animals there. The people who did not use the free land scarfice and the others who did benefited from the ecosystem service. However, sometimes overgrazing of villagers cattle caused the land to be degraded to the point that no one could use it.
Because no one is responsible for protecting a resource, and if humans do not preserve the goods and services of an ecosystem, these resources may suffer the same fate as the common grazing lands in English villages.

3. Importance of Biodiversity
Biodiversity- the sum total of the genetically based variety of all organisms in the biosphere.
Biodiversity is one of Earth's greatest natural resources. Species of many kinds have provided us with foods, industrial products, and medicines.
Can you think of products or services that are made from wildlife?
Biodiversity of beans provide food for people around the world
The variety of life in the world or in a particular habitat or ecosystem.
Rosy Periwinkle: has a substance used to treat cancer

4. Habitat Alteration
When land is developed, natural habitats may be destroyed.
Habitat fragmentation- is splitting ecosystems into small fragments
The fragmented habitats become biological “islands” which are pieces of land surrounded by other habitats.
Ex. A highway fragments a forest habitat and creates a biological island.
Habitat fragmentation can occur when land is developed and sectioned off. Habitat fragmentation can be as simple as a highway being built in a forest. The highway separtes the land on the left from the land on the right discontinuing or fragmenting that forest ecosystem.

5. Hunting Species to Extinction
Extinction- when an entire species dies off and there are none left in the world.
Endangered- a species whose numbers are so small that they are at risk of extinction
Gorillas and sea turtles are endangered because of hunting and fishing practices.
Seaturtles are hunted for their shell, leather, and fat.
Gorillas are hunted for bushmeat, and

6. Introduced or Invasive Species
Native species- plants and animals that are native to an ecosystem as a result of natural processes
Invasive species- plants and animals that have arrived to a place they do not naturally live in by the means of human activity
Example of introduced species Kudzu, the cane toad, the zebra mussel
In the late 1800s the Japanese brought over some of their plants and Americans discovered it could be used for forage. In the 1920 it was introduced as a forage pland and in the 1930s it was used to help prevent erosion.
Cane toads were introduced to Australia to control the cane beetle populations, but they did not eat the beetles, instead they eat everything else. Cane toads have no natural predators in Australia. Therefore, what do you think happened to their population?
The zebra mussel orignally is from Russia. Accidently introduced from the ballast water of ships or by attaching on to the ships anchor or bottom.

7. Toxic Chemicals
Dichlorodiphenyltrichloroethane or (DDT) was a popular pesticides in the 40s,50s, and 60s.
It was banned in 1972 because it was causing a lot of problems.
Rachel Carson wrote Silent Spring, a book that traced the path of DDT in the ecosystem.
A book by Rachel Carson titled Silent Spring was written about DDT. She traced the effects of DDD through the food chain.

8. Toxic Chemicals - DDT
DDT was sprayed on crops, in neighborhoods, etc. to kill mosquitos.
Excess DDT got into the river system.
The DDT began to move up the food chain.
DDT was found in high concentration in birds of prey such as eagles.
This was a very large problem because the DDT was making eagle eggs softer than normal and not many eagle offspring were being born.

9. Bioaccumulation & Biomagnification
Bioaccumulation is when toxic chemicals enter the food chain.
Biomanification is when the toxic chemicals move up the food chain.

10. What can we do to protect the environment?