Defining biodiversity

Biodiversity, a product of evolution

The term « biodiversity » is recent and has been diffusing since the international conference of Rio de Janeiro in 1992. Literally, this term designs the diversity of the living beings. To understand biodiversity we have to place ourselves in the frame of the evolution of the living things, since the biodiversity we observe today stems from this evolution. On large time scales, biodiversity is not fixed, it changes depending on the relations between the organisms and their environment. It is then difficult to study biodiversity as it depends on many links, the organisms with each other and with their environment. To illustrate this term, Robert Barbault, professor of Ecologie, had a nice analogy: “biodiversity is the living fabric of the planet”. Biodiversity can thus be observed at different scales, since not one gives a general view. To simplify, three scales are generally studied: that of the species, of the genes and of the ecosystems.

The diversity of species 

Since many centuries, the diversity of life has been described from the species. Even now, this level is very studied and is a first step to understand the living things, seeing as a huge number of species remains to be described. The number of species present is often the only criterion to study the diversity. If this method seems easy a priori, it is not representative of what is really biodiversity and gives a distorted outlook. Indeed, considering the evolution, the species will change over time, some species can be very close, or one species can have organisms with very different forms. This is the case of Hedge snails, snails of the same species with very different colors of shell!

The genetic diversity

To study this diversity within species, we can use the shape of the organisms, but the differences are often very small, so other methods can be implemented. This is the case of genetics. Genes are transmitted between an individual and its descendance and variations of form between individuals can come from a difference to the genes level. The different versions of the same gene are called alleles. Studying genes enables us to see the differences between species and within a given species, between the individuals. But if the diversity of the living beings can be linked to these genes, they are not the only factors, and do not inform us directly on the organisms’ relations with their environment.

The diversity of ecosystems

The last level, that of the ecosystem, goes beyond the species level by taking into account the organisms’ relations among each other (whether they are the same species or nor) and with their environment. The ecosystems, in other words the organisms, their environment, and the relations they have, can be very diverse because they include forests and rivers, but also animals intestines and puddles!

The three levels of diversity, consisted of species, genes and ecosystem, show the facets of biodiversity but it is comparing them that enables us to comprehend the « living fabric of the planet ».