What are the causes of wildlife extinction?

I know that humans are the main reason but i am looking on more in the deforestation as a main cause but not sure how to explain it.needing to be able to explain this to a ten year old fifth grader. any suggestions.
he has to have a poster made up showing the estimations of the current impact of deforestation on world. I have found some pictures of animals and plants that are extinct but how would do you figure out the impact they had on the world?

http://www.awionline.org/pubs/Quarterly/spring2001/wildlife_extinction.htm

http://www.google.com/search?hl=en&lr=&safe=active&as_qdr=all&q=deforestation+%22wildlife+extinction%22+

you can figure out the impact they had on the world by looking it up online or finding it in encyclopedias/your science textbook/or if you have a freind and your in the same class or even learning the same thing you can call them up and ask.

To explain deforestation and its impact on wildlife extinction to a ten-year-old fifth grader, you can use simple and relatable language:

Deforestation means cutting down trees in a big area of land. Trees are very important for animals and plants because they provide homes and food. When we cut down a lot of trees, it damages the homes and food sources of many animals and plants. They may not be able to survive without their homes and food, which can make them go extinct.

You can show the fifth grader pictures of different animals and plants, explaining that some of them are not alive anymore because they lost their homes and food due to deforestation. You can also explain that when animals and plants go extinct, it can have a big impact on the world. They could talk about how some animals help with pollination (like bees) or keep other animal populations in balance (like predators), and when they aren't there anymore, it can cause problems for the environment.

For the poster, you can show pictures of forests before and after deforestation to demonstrate the impact visually. You could also include a graph showing the increasing rate of deforestation over time.