Biodiversity

To me, biodiversity, simply means the number of plants and animals on the planet that are different from each other. The Smithsonian offers a more complex definition...

The vast wealth of life on earth is unified by a common strand: DNA. All living things owe their forms and functions to the molecular makeup of their DNA. But perhaps more intriguing than life's unity is its immense diversity. Biological diversity - biodiversity - is one of the central themes of conservation. But what exactly is biological diversity, and why should we be concerned about preserving it? Simply put, biodiversity may be defined as the measure of how healthy our ecosystems are. Healthy ecosystems support high biological diversity; while stressed or highly disturbed ecosystems do not. When we consider biodiversity as a whole, we are actually addressing 3 main components: genetic level biodiversity, species richness and ecosystem diversity. http://www.sms.si.edu/IRLSpec/Whats_biodiv.htm

Biodiversity is important to the planet. The more unique species we have the more likely life on Earth is able to survive disasters or changes in the environment.

For instance. We as Humans rely on farming for a great deal of food production. In times past we used many different types of crops, even of the same species. Take corn, we used to use many different varieties of corn and now the giant farms that mass produce corn only use the types that give them the greatest yield. The even go so far as to genetically modify the corn. The problem with this is that if some bacteria, fugus, bug, or virus evolved that was especially efficient in killing the type of corn we are producing, we would all be in a lot of trouble.

We can look at the Great Famine in Ireland as an example of what happens when a disease kills a crop that is a staple. In that case the disease was Phytophthora infestans and the crop was the potato. Around a million people died in that famine.

Of course that is only one example I can think of. I'm sure other people can think of more.