Biodiversity: what definition?

“Biodiversity” is a priori a word easy to understand because it is composed of the Greek prefix “bios” which means “life” and the term “diversity”. Biodiversity therefore designates the diversity, or variety, of life. But if we seek to delve into the notion of life, we can only note that it calls for being better defined in order to be truly understandable, as well as that of diversity that our societies seem to constantly scrutinize, generally only to do so. finding that it reduces. This article sets out the basic concepts to master in order to go a little deeper into the subject.

Where does the word “biodiversity” come from?

The term biodiversity has an inventor, all the better identified as his invention is recent. Indeed, the term was used for the first time by the American biologist Water G. Rosen, on the occasion of the first American forum on biological diversity which was held in 1986. Taken up by Edward O. Wilson, entomologist and professor at Harvard University, the term became popular in 1992 because widely used in the Conference of Rio de Janeiro (Brazil), event also known under the name of “Summit of the Earth”. Some scientists may have regretted that the term “biodiversity” has been so successful, because it is more effective in terms of communication, and has succeeded in replacing the previous terms, used for a long time and better defined: diversity of species or richness of species. .

The term biodiversity can indeed lead to misconceptions if one stays on the surface of the term. Seeking to better understand its contours constitutes the advantage of making us penetrate into the complexity from the universe of biology. For biologists, biodiversity is defined as the totality of genes, species and ecosystems in a region. Finally, talking about biodiversity is a way of unifying the necessarily fragmented view if we want to understand the richness of life. Biodiversity encompasses:

  • the diversity taxonomic, usually used to assess the level of diversity of identified species,
  • the diversity ecological which takes greater account of ecosystems as a whole,
  • the diversity morphological which focuses on genetic and molecular diversity,
  • and diversity functional which attempts to measure the variety of behavior of species by observing the different ways of eating, moving, etc.

The study of the past is necessary for understanding changes in biodiversity

The term biodiversity has spread with the idea that there is Man on one side and Nature on the other, and that the former has the responsibility of conserving the diversity of living things and of building a relationship. balanced with the planet and its different inhabitants. This has greatly contributed to simplifying the conception of Nature in non-specialist minds. The description of living things (which comes under taxonomy) and its classification (which relates to systematics) have evolved a lot since their appearance, and it is probable that these approaches will continue to evolve. Indeed, one describes and one classifies differently according to the degree of knowledge which one has of a subject. Knowledge itself changes the way we look at the subjects we seek to explore. The approach of Charles Darwin and the publication of Origin of species in 1859 gives important keys to soften the look that we can put on Nature, because his reflections led to understand that the living has nothing immutable but that its expressions vary over time. Some varieties may appear while others have disappeared.

Understanding the current biodiversity requires knowing the evolution of life and its forms. However, the oldest data gathered by naturalists date from the 19th century: in the end, this remains relatively little on the scale of the existence of life on Earth. Yet we also need to understand beyond just our industrial societies. This is why Prehistory and History contribute in a fundamental way to a necessary step back. Sciences such as geology, paleobotany and archaeozoology provide essential information to enrich our approach to biodiversity and the understanding of its evolution over several centuries.

Biodiversity today

Despite the constant improvement in our knowledge and the functioning of the planet, we must remain humble because a lot of things still escape us. The quantification of biodiversity on a planetary scale is still an exercise that seems impractical. If 2 million species are inventoried, this figure remains debated for two reasons. The first is that there is no harmonized global taxonomic repository. The second is that we estimate (but this is also discussed) at approximately 10 millions the total number of species present on Earth. Thereby, only 20% species would be described. Complete knowledge therefore seems impossible, all the more so since, even if we discover about 10,000 species each year, mainly arthropods, others most certainly disappear before we have even had the time to describe them.

The logics which govern the distribution of biodiversity are now well known. While there are always exceptions, here they are:

  • the richness of the species increases from the poles towards the equator,
  • the richness of species decreases with altitude,
  • the richness of marine species is generally greater at depth.

It is also known that the spaces which host the greatest diversity are mainly located in the tropics. Marine biodiversity is known differently from continental biodiversity: the oceans cover more than 70% of the earth’s surface, but only 15% of the animal and plant species described are marine. However, from a taxonomic point of view, the distribution is reversed: among the 33 phyla of metazoan animals described, 28 are marine.

Biodiversity has experienced five major extinction crises. The Ordovician Crisis 500 million years ago saw half of all animal families disappear. The Devonian Crisis 345 million years ago saw a third of animal families disappear. The Permian Crisis 250 million years ago also saw half of all animal families disappear, 95% of which were marine animals. During the Triassic crisis 180 million years ago, 35% of animal families disappeared. Finally, the Cretaceous crisis is undoubtedly the best known since it was this which saw the disappearance of the dinosaurs.

Today the existence ofa sixth crisis is identified. This is experiencing a marked decline in mammals, birds and amphibians. Human activity is clearly identified as its cause. This situation has led to the emergence of a discipline of crisis: conservation biology. But the choice of the elements of biodiversity to be conserved as a priority is the subject of debate. The urgency of the situation undoubtedly makes intervention essential. But how can we be sure of the correctness of our actions in a context where the state of our knowledge is still so partial?