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Unit 4

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Lesson Plan 3

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Concepts/Objectives | Vocabulary/Background | Activity | Extension


Lesson Plan 3




Extinction: When a certain type of animal or plant no longer exists.
Exotic species: A species that is not native to the region; it has been introduced by humans.


Animals become extinct for several reasons: sometimes animals are hunted, killed, or pollution kills them, their home is destroyed or their food is taken away, and occasionally environmental changes take place so that they no longer can survive. When there are too few of animals of a species left, the species can no longer successfully reproduce itself, no more individuals are born and the species becomes extinct.

Brown Pelicans are a good example of an animal which almost became extinct. In the 1960's they were on the brink of extinction and no one understood why. A scientist at the Los Angeles County Natural History Museum, Ralph Schrieber, discovered that DDT was the source of the near extinction. The egg shells were breaking and no young brown pelicans were being born. This was one of the first discoveries of how DDT affected wildlife.

Even the largest species are not immune to these problems of extinction!

The Gray Whale which travels through the San Pedro Channel on its long migration from Alaska to Mexico, had previously become an endangered species. Historically it was killed in vast numbers for its blubber and meat. They were in danger of extinction and therefore became protected. Now their numbers are increasing and they have been moved off the endangered speices list but are still protected against whaling.

Currently other fish that often end up on our dinner plate are being overfished and could possibly one day be threatened: tuna, shark, swordfish and halibut fall in this area. An important thing to remember about overfishing is that it is not just the number of the fish that are taken that affects a population, but also the age. If you take the younger fish then they cannot grow up to have baby fish and the population is decreased quite rapidly.

Catalina Island once was home to the California Sea Otter, but they were killed off for their fur pelts. Now only a sub-species exists at Monterey Bay and because their numbers are so limited they could be wiped out. Efforts to re-introduce sea otters to Southern California have met with objections from the fishing industry (due to competition for abalone). Also a re-introduction attempt at another Channel Island (San Nicholas Island) was a failure. The re-introduced sea otters all disappeared and it is unknown if they simply swam away or were killed by fisherman (who had threatened to shoot them).

It is important to note that with the sea otters gone it has changed the local ecosystem. Sea otters ate sea urchins and the sea urchins ate kelp. By upsetting the predator/prey balance it interferes with the web of sea otter/sea urchin/kelp forest. The sea urchin population increased due to the removal of sea otters and also lobster and sheephead which eat sea urchins are also being over fished. The lobster and sheephead fish ate also ate sea urchins. The increase in the sea urchin population (plus the effects of "El Nino" --which is a change in a major ocean current which affects upwelling and food sources) contributed to decrease in kelp.

On land in Southern California other extinctions have almost occurred. One of these is the El Segundo Blue Butterfly. Due to housing and industrial development, the type of plant that the Blue Butterfly lived on was almost completely destroyed. When plants, which are an animal's food source, are destroyed so is the animal that depends on them. This is happening on Catalina Island, as plants are destroyed due to overgrazing (by animals that were not originally on the island) the animals that rely on those plants become threatened. (NOTE: this is an example about Catalina can be an opportunity to discuss what is an "exotic species"---and why it is a problem)