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.

Types /level of biodiversity:

There are 3 types /level of biodiversity. They are:
Genetic diversity.
Species diversity.
Ecosystem diversity.
Genetic diversity:
Genetic diversity occurs within and between types of species as well as between species. It means the variation of genes within species. Chromosomes, genes, and DNA determine the uniqueness of each species. This includes genetic variation within species, both among geographically separated populations and among individuals within a single population. This genetic diversity is result of different modes of adaptation in different habitats, providing organisms and ecosystems with the capacity to recuperate after change has occurred. Thus, this diversity can be viewed in three levels:
Diversity among species.
Genetic variability between individuals within population.
Genetic variability among population within species.
Genetic diversity can be measured within a variety of DNA and other techniques. The part of genetic variation present in an interbreeding population is shaped by selection.
Species diversity:
Species diversity refers to the variety of living species. This diversity denotes the variety of species on earth from as cellular viruses to single celled microorganisms like bacteria, mycoplasmas, agronomists etc, to multi cellular plants and animals. For proper functioning of a particular community or ecosystem, species diversity is very essential. In a community the survival of all species is interrelated to the existence of other living organisms. Aspects of species can be measured in a number of ways. Most of these ways can be classified into three types of measurement, they are listed below:
Species richness.
Species abundance.
Species taxonomic or phylogenetic diversity.
The main reason for species diversity is variation in physical aspect.

Introduction:

The term biodiversity occurred in middle of 1985AD for study of variety and prevalence of species of animals and plants. The term biodiversity, which represents the very foundation of human existence, was coined by Walter G. Ros en in 1985for the 1st planning meeting of the "National Forum on biodiversity " held in Washington, DC in September 1986, the proceedings of which brought the notion of biodiversity to the attention of a wide field scientists and others. However, the credit for popularizing this word goes to E.O. Wilson who is often called the "Father of biodiversity".
Biodiversity or biological diversity refers to the variability among living organisms from all sources including terrestrial, marine and aquatic ecosystems and the ecological complexes of which they are part; this includes diversity within species, between species and of ecosystem. The existence of a wide variety of species or other types of plants, animals and micro organisms in a natural community or habitat, or of communities within a particular environment or of genetic variation within a particular species is called biodiversity. All living things are a bit different from each other. While some will perish, there will be others who would have certain genes or characteristics that will help them survive the calamity. This variability, also known as biological diversity, is a big defense mechanism essential for the survival of nature in all its pristine glory.