Elena Casetta

After having reconstructed a minimal biological characterisation of species, we endorse an “empirical approach” based on the idea that it is the peculiar evolutionary history of the species at issue—its peculiar origination process, its peculiar metapopulation structure and the peculiar mixture and strength of homeostatic processes vis à vis heterostatic ones—that determines species’ identity at a time and through time. We then explore the consequences of the acceptance of the empirical approach in settling the individuals versus kinds dispute. In particular, while conceptual arguments have been proposed to show that species can be equally treated as individuals and kinds because mereology’s and set-theory’s languages are inter-translatable, we advance instead a causal argument to sustain the claim that each species is both a kind and an individual.

Despite increasing communication, accelerating policy and management responses, and notwithstanding improving ecosystem assessment and endangered species knowledge, conserving biodiversity continues to be more a concern than an accomplished task. Why is it so? The overexploitation of natural resources by our species is a frequently recognised factor, while the short-term economic interests of governments and stakeholders typically clash with the burdens that implementing conservation actions imply. But this is not the whole story. A different perspective on the problem shall here be considered, by exploring the conceptual and practical challenges posed by conserving biodiversity.

In recent years, we have assisted to an impressive effort to identify and catalogue biodiversity at the microbial level across a wide range of environments, human bodies included (e.g., skin, oral cavity, intestines). This effort, fostered by the decreasing cost of DNA sequencing, highlighted not only the vast diversity at the microbial level but also the importance of cells’ social interactions, potentially leading to the emergence of novel diversity. In this contribution, we shall argue that entities other than species, and in particular multispecies biofilms, might play a crucial—and still underestimated—role in increasing biodiversity as well as in conserving it. In particular, after having discussed how microbial diversity impacts ecosystems (Sect. 9.1), we argue (Sect. 9.2) that multispecies biofilms may increase biodiversity at both the genetic and phenotypic level. In Sect. 9.3 we discuss the possibility that multispecies biofilms, both heterotrophic and autotrophic, are evolutionary individuals, i.e. units of selection. In the conclusion, we highlight a major limitation of the traditional species-based approach to biodiversity origination and conservation.