According to the rather lengthy reference site pasted in below, you likely want to take a closer look at the three types of diversity included in "biodiversity,"
- genetic diversity
- species diversity
- ecosystem diversity
Because they represent rather different concepts, it is important to make it clear which aspect of biodiversity is being talked about.
One of the other themes that runs through most thoughts about biodiversity is that it is varied depending on the actual physical location, most people look to the tropics because of the increased density of species and varieties of flora and fauna found there as places for intense biodiversity. If you go to the opposite perhaps at the North Pole, you see a place where there is little to no biodiversity (unless of course you go under the North Pole into the ocean where there is quite a bit.)
Biodiversity describes the differences in all life forms whether they live in a particular ecosystem or biome. We can also look at biodiversity on a global level.
Biodiversity is higher in areas where there are more living things such as in tropical habitats. Tropical habitats have a very diverse population of plants and animals. If we look at a polar region we will still see diversity but since there are not as many living things there it will not be as diverse as a tropical region.
A key concept that I would consider when thinking about biodiversity is the changing environment. The environment is changing at a very rapid rate. Many animals are becoming extinct and this is very relevant to biodiversity and change. Humans are also making a huge impact on the biodiversity of the Earth in general. Humans are causing a reduction in plants and animals because we are destroying their habitats.
Biodiversity is the variation that exists within a group and can be generalized to a population, ecosystem or the biosphere. Biodiversity is not consistent across the globe and it is dependent on genetic variation.
Think of the different types of biomes that exist (desert, tundra, tropical to name a few) and think of the types of organisms that live in these environments. Each environment hosts its own biodiversity and as you expand to the entire earth the diversity increases. The organisms best suited to live in each environment are able to survive and reproduce; increased ecological variation leads to increased biological diversity. As humans continue to destroy various environments biodiversity is lost.
Genetic variation leads to new adaptations and creates differences within a species and creates new species. Genetic variation is a result of sexual reproduction. Without sexual reproduction DNA would not be "mixed up" and therefore would not lead to differences with in species, natural selection and evolution which in turn would not develop a world rich in biodiversity.