1. Current confusions

The question arises as to what kind of diversity we are talking about when we talk about biodiversity: that of organisms or that of their interactions? “Both”, ecologists tend to answer. “Not so fast”, will suggest the epistemologist: just because we consider the mosaic of species communities that make up a landscape (the third level of biodiversity) does not mean that we are necessarily interested in indentifying the various links binding these communities. The recurrence of species assemblages is what makes them distinguishable as communities. The skill of the systematist is all that is needed to characterise the assemblage. Each structuring level of reality deserves to be characterised. No one would ignore or deny the need to characterise species, subspecies and even populations, but as soon as the issue of characterising communities of species is raised, the task is seen as a study of interactions, thereby obscuring compositional characterisation. However, whether an ecologist or a systematist is characterising communities in a landscape, the question is one of systematics, not of ecology: we continue to describe what is there, and the spatial segregation of entities does not change that. The issue here is not functional relationships, but a relatively perennial compartmentalisation of living things, which is recurrently found. Furthermore, the use by ecologists of concepts of systematics to characterise communities of species does not mean that they are asking questions about systematics, or that ecology includes systematics. Twenty-five years ago, the French Académie des sciences produced a report on the state of systematics in France [8], which discussed the scientific autonomy of the discipline. This report addressed the confusion between being a user of systematics—almost any profession in contact with living organisms—and being a systematist, i.e. a scientist who conducts research in systematics.

Moreover, the definition of biodiversity dates back to the late 1980s, when geno-centrism was in full swing. Intraspecific diversity could only be genetic. And this is still what is taught today. All exhibitions on the subject speak of infraspecific diversity only in genetic terms, as do our ministries​​​​​​​⁷ , or Wikipédia⁸ , for example. Yet explanations of the variability observed in the living world no longer focus exclusively on the gene, but also on the organism. Variations can exist, and sometimes be passed on through mechanisms beyond the gene, such as accidents or modulations in embryonic development [9], certain behavioural components, cultural variations [10, 11, 12], and those known as “epigenetic” variations. We are beginning to glimpse the evolutionary effects of some of these [13, 14]. Genes are still important, but we now recognise that such effects can be attributed to variations transmissible through channels other than genes, at a level of integration linked to the organism. In short, it is important today to bear in mind that intraspecific diversity is not just genetic, because the sources of these heritable variations are involved at several levels of integration within the organism.

The concept of Biodiversity (judged too all-encompassing by [6]) could have been scientifically useful if it had not confused everything, i.e. the study of what there is (the characterisation of diversity) and the study of what it does (the characterisation of functional interactions between living beings). This confusion is found among members of the Académie des sciences, in the collective “Libres points de vue d'Académiciens sur la biodiversité” [15]. When two academics were asked “What is biodiversity?”, one did not include interactions in the definition, while the other did [15, p. 6]: “Biodiversity is therefore all the diversity of living organisms, broadly structured into genetic diversity, species diversity, diversity of forms, functions and interactions”. When four academicians were asked the question “Does the study of biodiversity only concern the census of living species?”, two academicians maintained a clearly systematic epistemology, while the other two subordinated biodiversity to the ecosystem and its study to the study of interactions, e.g. on p. 7 : “But a simple inventory of living species would only give a very partial understanding of the diversity of the functioning of living organisms. Each individual interacts with members of its own species within a population, each species with other species; all these species use resources and recycle matter and energy within larger ecological systems, the ecosystems”; or p. 11: “The study of biodiversity cannot be limited to a census of living species (...) it must also make it possible to specify the role of biodiversity in the functioning and dynamics of ecosystems, for example with regard to their productivity and stability in the face of disturbances of varying degrees of severity (...) Nevertheless, the study of biodiversity cannot be developed without a census which, it must be acknowledged, is still only partial”. This last opinion generously grants biodiversity the only analytical prism that, in my opinion, can give meaning to the concept. Within the same ideological framework, and probably unconsciously, the INPN's definition of biodiversity⁹ refers to the study of functioning as an improvement (the description of living organisms remains behind, relegated to an already completed task): “Today, we are still studying the components of biodiversity (inventories of ecosystems, flora and fauna), yet we are increasingly seeking to understand how it functions. We have reached a new stage in our understanding of the system, moving from its description to the study of how it works”. Systematics is an outdated science, a view echoed at the beginning of Robert Barbault's book [1], as discussed in [16]. As a result, confusion now exists about the respective uses of the terms “biodiversity” and “ecosystem”, which have become virtually interchangeable in the general public's usage.

To overcome these confusions, the ecosystem must remain what is examined when documenting the interactions between species in a given environment, or between these species and the abiotic environment, regardless of the scale considered. Since these interactions are part of the definition of biodiversity, either “ecosystem” and “biodiversity” are synonymous, or “ecosystem” is a subset of “biodiversity”. However, it is difficult to see how the latter option could be possible. Indeed, if “ecosystem” is only a subset of “biodiversity”, there must be entities that come under the heading of biodiversity that cannot be understood through the prism of the ecosystem. This is impossible, because there are no living beings that are not in relationship with others. Therefore, introducing interactions into the definition of biodiversity (at its third level) makes the concepts of ecosystem and biodiversity superimposable, and renders the concept of biodiversity useless. There is no need to look for a distinction in the first two levels: we know of no specific diversity that is not part of an ecosystem; we know of no individual conspecific organisms that are not part of an ecosystem.

2. Systematics and taxonomy deal with what is there, ecology with what it does

For biodiversity to be a scientifically operational concept, interactions must not be included, which are then reserved for the ecosystem. If we do not include interactions in the definition of biodiversity, the ecosystem is no longer synonymous with it, but this does not diminish its significance: it remains what constitutes the interactions between organisms among themselves (biocenosis) on the one hand, and between organisms (biocenosis) and their environment (biotope) on the other. In short, an ecosystem is defined by what organisms do with each other and with the environment. Ecosystems are studied by ecology, geochemistry, pedology, geology, meteorology, etc. Biodiversity would then be what is examined when characterising what organisms have (their structures) and are (how we refer to them), at all scales, from the individual to the population, from the population to the species, from the species to assemblages of species. Biodiversity is then studied by systematics and taxonomy, informed by the sciences that compare and characterise structures.

The common confusion in the use of the terms “biodiversity” and “ecosystem” is also undoubtedly due to the fact that these two modes of apprehending reality address the same entities: in the former case, the focus is on what they are; and in the latter, it is on their interactions (Figure 1). This can lead to tensions between scientists, as it does in politics: taking power or capturing resources always involves reclaiming concepts and lexicon. A political or administrative round table is indeed a strange place where all sorts of tricks are allowed when it comes to manipulating concepts, but where any rectification is forbidden for fear of drowning the meeting in a “quarrel between specialists”, a pejorative term designed to protect the ideology at work. Epistemology and politics cannot coexist on a board of directors, or even on the scientific board of any research institution. The latter manipulates the former. This should come as no surprise. When politics involves power relations, its power depends on an ideological framework that is all the more effective for having rewritten history and redefined words to suit its needs. This is undoubtedly where the term “biodiversity” comes from: a new term was needed for political reasons. Today the confusion is such that, even among scientists, words have sometimes lost their meaning. For example, the characterisation of living beings in a given environment by metabarcoding (i.e. the identification of populations and species present through the analysis of a small piece of their DNA sequences) is described as “molecular ecology”, even though the concepts and methods used actually are those of molecular systematics. Indeed, the question is what is there and how much there is in a given place, not what it does. The people involved are not even aware of this. In universities, the “molecular ecology” curriculum teaches the conceptual content of molecular systematics, not that of ecology. Moreover, taxonomy is taught in the context of ecology rather than systematics, which can lead to many inaccuracies.

To conclude on a positive note, biodiversity was a useful concept at the end of the 80s because it drew attention to a point of caution: measuring the diversity of living organisms should not only be done by counting species. It was also necessary to take into account the diversity within each species, which was crucial for estimating its evolutionary potential, as well as the diversity of communities in a given landscape, in other words whether the landscape was formed by a homogeneous assemblage of species or whether it was composed of packets of species that were distinct from each other. Today, to save the concept from intellectual vacuity, we need to clarify its relationship with the ecosystem, by restricting biodiversity to the exactness of its etymology: it is what is studied when the biological diversity of what there is at all levels is examined. Walter G. Rosen has removed “logical” in the expression “Biological diversity”. But logic ought to come back.

Declaration of interests

The author does not work for, advise, own shares in, or receive funds from any organization that could benefit from this article, and has declared no affiliations other than his research institution.