Reasons to defend and promote biodiversity

On May 22 just ended it was declared “world biodiversity day”; I would therefore like to take advantage of this anniversary to shed, as a biologist, some light on what we intend to bring to everyone’s attention on this occasion. From many quarters, we hear the promotion of the conservation and increase of biodiversity as values, and since, at least in words, this objective is now incorporated by politics at various levels, national and international – and therefore through the public administration we are all and we will be increasingly driven to coherent actions in this sense – I think it is first of all necessary to be clear about what we are talking about, both in terms of the definition of the asset that we intend to protect, and in terms of what the actual value would reside in such protection.

As my friend Paolo always reminds me, for a conversation to be useful you need to be very sure that you intend to discuss the same thing, especially if you intend to reach an agreement that influences our actions, as in this case. In the first instance, one might think that the variety of species in that environment lies at the basis of the definition of biodiversity in a given environment. However, this is a definition that is problematic in many cases: for example, a zoo would have a greater biodiversity than a mountain pasture, and therefore, as regards policies to increase biodiversity, we should promote the establishment of zoos . In the same way, the crop varieties of a single species such as, for example, those of certain fruit trees or vines, which are intended to be preserved as a source of biodiversity for our agriculture, could not fall within the definition, being in each case, of individual species. For reasons such as those illustrated, in modern ecological science biodiversity is measured on several levels, with appropriate indices useful for each level, indices which, then gathered in appropriate profiles, allow the biological diversity of the living community which it occupies to be compared and evaluated. a given environment.

We start from taxonomic diversity, which is not simply proportional to the number of different species, but also to the number of other taxonomic categories, of a higher order; thus, to take an extreme example, an environment in which there are hundreds of species, but all belonging only to bacteria, will be considered less diverse than one in which there are a comparable number of species, but belonging to all living kingdoms. This diversity is directly related to the genetic and morphological variety indices of the species present in a certain environment: the more that environment contains distant and varied organisms in terms of genetics and phenotype, the more it will be considered to have high biological diversity – which explains the example just given, just as it explains why crops with many varietal differences (genetically and morphologically distinguishable) are considered to have greater biological diversity than those characterized by greater homogeneity, regardless of whether a single species is considered. It is not enough: in fact, a community of organisms will be considered more different in which there is a greater difference in functional adaptations, or in different ways of obtaining the energy necessary to fuel one’s own metabolism, in behavior to escape predators and in under the most varied environmental conditions possible.

There functional diversity it is measured through indicators of the overall metabolic complexity of a living community (linked to how many resources can be exploited as food, how many transformation steps are possible, the variety of non-food energy sources, etc.), behavioral (more difficult to measure, linked for example to the complex of cognitive and innate behavioral modules implemented to perform defined functions) and adaptive (linked to the variety of physiomorphological adaptations not directly connected to metabolism, but for example to protection from adverse conditions, exploitation of favorable ones and reproduction). So far, the zoo of our initial example should be considered as having a high biological diversity, and as far as the indicated parameters are concerned it certainly is; but there is a further level to consider, namely that of ecosystems. An ecosystem, in particular, is defined by the functional relationships between different species: primary consumption, predation, symbiosis, non-obligated cooperation, parasitism, competition for physical and metabolic resources are all examples of relationships involving different species and define the so-called ecological network .

The complexity of this network and of its possible evolution over time, measurable for a given community of living beings thanks to parameters derived from graph theory, provides a further parameter for measuring biological heterogeneity, and is, of course, the one which distinguishes, for example a zoo from an alpine pasture, because in the first the interactions between different species will be very limited, while in the second they will be common, making it more biodiverse. Bearing in mind this multilevel definition of biodiversity, which incorporates taxonomic/genetic, functional and ecological variety, one can at this point ask why, given a certain environment, it is preferable to maintain a high biodiversity in it. In other words, we need objective parameters to examine what the value, positive or negative, of a policy that promotes biodiversity could be. In this sense, we are helped by an extensive review of literature data, published in Nature in 2012, which examines 25 different effects commonly attributed to the increase in biodiversity: even if more than a decade old, this review considered more than 1700 previous studies, and therefore still represents very solid and reliable work. We learn from this analysis that an increase in biodiversity in terms of plant species present in a given environment, individuals and biomass being equal, increases the yield of wood in a forest and that of forage in pastures, confers resistance to the entry of plants invasive alien, increases carbon dioxide sequestration (but not necessarily storage), favors the remineralization of nutrients and increases organic matter in the soil. Furthermore, a greater variety of plants decreases the abundance of plant parasites, among other things also by increasing their natural enemies, and ultimately decreases the prevalence of plant diseases.

As for the animal biodiversityAs an example of a positive effect, the authors find that an increase in fish species stabilizes farm production. Instead, there are many cases in which the evidence is conflicting or solid data is lacking: while the high genetic diversity of farmed plants increases, for example, crop yields, it is not clear whether this also applies to different species or whether the variety is sufficient of cultivars; in no case is it certain that the stability of these yields is increased by plant biodiversity, and this also applies to forest and forage production. The ability to store carbon and its correlation to plant biodiversity is not proven, as there is conflicting evidence, as well as conflicting evidence about the decrease in parasites as animal biodiversity increases. Even the most classic of the effects usually invoked, the increase in pollination efficiency as the biodiversity of pollinators increases, appears to be unsupported for now, because in this case too the data are conflicting. The role of plant variety in erosion control, improved soil moisture and – of interest these days – improved flood containment, does not show sufficient general support, due to lack of data. Then there are cases in which expectations are decidedly contradicted by the data: a greater variety of plant species, for example, is not correlated to an increase in primary productivity, and a greater biodiversity of water is not correlated to their purification.

Of course, even without considering that further evidence has emerged in the ten-plus years since the publication of the work discussed here, one point should be clear: in the face of advantages that are not sufficiently proven or even denied, there are a good number of certain ones, all related to the increase in biodiversity of specific components of the different ecosystems studiedthe; and this without considering other advantages, more anthropocentric but no less important, such as the recreational, cultural and aesthetic values ​​that biodiversity promotes. The reasons of those who intend to protect biodiversity therefore seem well founded; but how and where is it possible to promote biological diversity? We’ll talk about it later.