We shape landscapes ever more strongly around our needs. What serves no recognisable purpose can quickly appear dispensable. Yet this contains a hidden error: we judge species by functions we already know, even though much of their capacities and relationships remains unknown.
Imagine a landscape consistently tailored to human purposes: fields produce what we eat or sell, forests provide timber, rivers are engineered for water supply and flood control, and infrastructure occupies clearly defined space. The more consistently we optimise such a landscape, the more plausible a provocative question becomes: why do we still need so many species?
Growing maize does not require every species
For a single function, not every species is indispensable. Biodiversity research likewise shows that individual ecosystem functions can display saturating relationships with species richness; when several functions are considered, more species can be required because different species contribute to different functions.[1]
The hidden step is that before deciding which species we “need”, we have already decided what we need them for. Use defines the function; the function then defines what appears useful or superfluous.
A bacterium and a plastic bottle
In 2016 researchers identified Ideonella sakaiensis, a bacterium capable of degrading PET and assimilating its breakdown products under the laboratory conditions studied.[2] The study does not establish whether this capability arose as an adaptation to PET. The bacterium does not solve the global plastic problem. Its significance here is epistemic: an organism possesses biochemical capabilities relevant to a human-made material. The example illustrates how difficult it is to predict which capabilities of an organism may one day become significant to us.
Life under radiation
The melanised fungus Cladosporium sphaerospermum was observed in radioactively contaminated areas at Chernobyl. Laboratory work found that ionising radiation altered melanin's electronic properties and that irradiated melanised fungi showed enhanced growth under the studied conditions.[3] Whether the fungi actually make ionising radiation metabolically usable remained a hypothesis of the authors. Saying that such fungi simply “feed on radioactivity” goes beyond the established evidence.
PET and the observations associated with Chernobyl do not prove that nature contains a ready-made answer to every human problem. They illustrate something more fundamental: we do not fully know what life is capable of.
When is a species redundant?
Species may be similar with respect to a particular function. Eisenhauer and colleagues have argued for the more precise language of “functional similarity”, explicitly tied to function, environment and context.[4] Fischer and de Bello counter that functional redundancy retains distinct ecological value as a concept.[5] Species that are similar may perform a comparable function under present conditions and still respond differently when conditions change.
Ecosystems also perform more than one function. Measured biodiversity–multifunctionality relationships depend on the identity and number of functions considered.[6] The analytical method also affects the measured relationship.[7]
“We do not need this species” therefore initially means only: we do not need it for a particular known function under particular known conditions.
The biological space of possibilities
Within the IPBES framework of Nature’s Contributions to People, maintenance of options (NCP 18) describes the capacity of ecosystems, habitats, species or genotypes to keep options open for a good quality of life.[8] This article calls the totality of these options a “biological space of possibilities” – a journalistic shorthand, not an established scientific term.
This does not mean every species must someday prove useful to humans. The key issue is the limit of our knowledge. We do not even know the exact number of species on Earth. Mora and colleagues estimated about 8.7 million eukaryotic species in 2011 (± 1.3 million, standard error) while emphasising the uncertainty of indirect estimation.[9]
When a species disappears, we do not necessarily lose a known indispensable function. But biological possibilities and relationships can disappear before we even know that they exist.
This limit to our knowledge does not mean that every species must be given equal weight in every circumstance or that conservation can do without priorities. Decisions about protection, use and competing objectives remain necessary. They should simply not rest on the broader assumption that the absence of a function recognisable today makes a species dispensable.
This says nothing yet about any intrinsic value species may have. This article deliberately addresses only the narrower, instrumental question of whether our present knowledge allows us to infer that a species is dispensable.
The blind spot of the standardised landscape
The more a landscape becomes a standardised production surface, the more our chosen use determines which functions are visible and relevant. “Not required for our present use” can quietly become “not required”. The latter does not follow from the former.
We may be standardising the Earth faster than we are learning about its biological possibilities.
So do we need every species?
Science offers no simple answer. It would be too easy to claim that every species is indispensable for every conceivable function. The opposite claim is at least as problematic.
Perhaps the decisive biodiversity question is therefore not: How many species do we need?
But: How do we know which species we do not need?
As long as we cannot answer that question, the claim that a species is dispensable reaches further than our knowledge.
Sources and notes
- Hector, A.; Bagchi, R. (2007): Biodiversity and ecosystem multifunctionality. Nature 448, 188–190. ↩
- Yoshida, S. et al. (2016): A bacterium that degrades and assimilates poly(ethylene terephthalate). Science 351, 1196–1199. ↩
- Dadachova, E. et al. (2007): Ionizing Radiation Changes the Electronic Properties of Melanin and Enhances the Growth of Melanized Fungi. PLOS ONE 2(5): e457. ↩
- Eisenhauer, N. et al. (2023): Reconsidering functional redundancy in biodiversity research. npj Biodiversity 2, 9. ↩
- Fischer, F. M.; de Bello, F. (2023): On the uniqueness of functional redundancy. npj Biodiversity 2, 23. ↩
- Meyer, S. T. et al. (2018): Biodiversity–multifunctionality relationships depend on identity and number of measured functions. Nature Ecology & Evolution. ↩
- Gamfeldt, L.; Roger, F. (2017): Revisiting the biodiversity–ecosystem multifunctionality relationship. Nature Ecology & Evolution. ↩
- Faith, D. P. (2021): Valuation and Appreciation of Biodiversity: The “Maintenance of Options” Provided by the Variety of Life. Frontiers in Ecology and Evolution 9:635670. ↩
- Mora, C. et al. (2011): How Many Species Are There on Earth and in the Ocean? PLOS Biology 9(8): e1001127. ↩
This article, including the accompanying AI-generated image, is licensed under CC BY-NC-SA 4.0. Structure and parts of the wording were developed with the assistance of AI (GPT, OpenAI). Editorial responsibility: Hans Leo Bader.