- Biological diversity has no single standard definition. One definition holds that biological diversity is a measure of the relative diversity among organisms present in different ecosystems. "Diversity" in this definition includes diversity among species, within species and comparative diversity among the types in different ecosystems.
- Another definition, simpler and clearer, but more challenging, is the totality of genes, species, and ecosystems of a region. An advantage of this definition is that it seems to describe most instances of its use, and one possibly unified view of the traditional three levels at which biodiversity has been identified
- Genetic Diversity - diversity of genes within a species. There is a genetic variability among the populations and the individuals of the same species
Species Diversity - diversity among species
- Ecosystem Diversity - diversity at a higher level of organization, the ecosystem (richness in the different processes to which the genes ultimately contribute)
- The latter definition, which conforms to the traditional five organisation layers in biology, provides additional justification for multilevel approaches.
- The 1992 Earth Summit in Rio de Janeiro defined biodiversity as
- The variability among living organisms from all sources, including, inter alia, terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are part: this includes diversity within species, between species and of ecosystems
- This is in fact the closest we come to a single legally accepted definition of biodiversity, since it is the definition adopted by the United Nations Convention on Biological Diversity. The parties to this convention include all the countries on Earth with the exception of Andorra, Brunei Darussalam, the Holy See, Iraq, Somalia, Timor-Leste, and the United States of America.
- If the gene is the fundamental unit of natural selection, thus of evolution, some, scientist like E.O. Wilson, say that the real biodiversity is the genetic diversity. However, the species diversity is the easiest one to study.
- For geneticists, biodiversity is the diversity of genes and organisms. They study processes such as mutations, gene exchanges, and genome dynamics that occur at the DNA level and generate evolution.
- For biologists, biodiversity is the diversity of populations of organisms and species, but also the way these organisms function. Organisms appear and disappear; sites are colonized by organisms of the same species or by another. Some species develop social organisations to improve their reproduction goals or use neighbour species that live in communities. Depending on their environment, organisms do not invariably use the same strategies of reproduction,
- For ecologists, biodiversity is also the diversity of durable interactions among species. It not only applies to species, but also to their immediate environment (biotope) and the ecoregions the organisms live in. In each ecosystem, living organisms are part of a whole; they interact with one another, but also with the air, water, and soil that surround them.
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