Causes of biodiversity:

There are many causes biodiversity; some of them are listed below:
Ecosystem
Gene
Species
Cross reproduction
Evolution
Ecosystem: The array of living organisms found in a particular environment together with physical and environmental factors that affects them is called an ecosystem. Different animals and plants are found in different ecosystem on the basis of their adoptive characters. So, it causes biodiversity.
Gene: Gene is visualized as a discrete particle and forming part of a chromosome, that determines a particular characteristic. It is composed of DNA. And it carries the hereditary characteristics. Different animals have different gene, so their characteristics are also different. So, it is also one cause for biodiversity.
Species: A species can be defined as a group or population of similar organisms that is reproduced by interbreeding within the group. And it is affected by topographic variation. According to topographic variation different species are found and causes biodiversity.
Cross-reproduction: Here, cross reproduction refers to the reproduction that occurs between two species. And by fusion of their gametes another new organism is reproduced with new and different characters. Then they form an ecosystem and live there, this causes biodiversity.
Evolution: The gradual process by which the present diversity of plant and animal life arose from the earliest and most primitive organisms, which is believed to have been continuing for at least the past 3000millions years is called evolution. So, it causes biodiversity by the development of different animals, change in climate and even environment.