What’s So Good About Biodiversity?

Sometimes, there are books you wish you wouldn’t have read. Mostly, these are bad books. Recently, I read a quite good book that I nevertheless first wished had escaped my attention. It’s Donald S. Maier’s What’s So Good About Biodiversity: A Call for Better Reasoning About Nature’s Value. It’s shaken up my view of why biodiversity is valuable (although not as much as initially thought). As I had to think a lot about Maier’s provocative and very polemic argumentation, for it has posed a challenge to the core of my PhD thesis, I would like to attempt a “self-therapeutic” review of his book’s first part, in which he attacks the status of biodiversity as carrier of nature’s value (I haven’t yet read his exposition of an own account why nature is valuable).

Let’s start with a few general points. Donald S. Maier calls himself “an environmentalist, trained as a scientist, and a moral philosopher by current profession”. He knows a lot about biological theories and concepts, but analyses them from an ethical perspective mainly. His main question, suggested in the title of his book, is: what (if anything) makes biodiversity valuable? The summary of his elaborate answer is: nothing. Biodiversity is, according to Maier, the wrong concept to choose as the carrier of nature’s value. Here, we already encounter one of the main caveats I shall make in my review: he assumes that nature’s value is viewed entirely through the biodiversity lens, and criticises the notion on this basis. While making his argument more clear, this also makes it less powerful than it seems in the first place. As soon as you acknowledge that biodiversity constitutes only one aspect of nature’s valuable essence, many of Maier’s arguments lose their force. Furthermore, it is sometimes annoying how polemic he is–most of the time, he attacks a few specific contributors to the vast biodiversity literature, particularly Edward Wilson, Sahotra Sarkar and Daniel Faith. This creates the impression that his critique might be applicable only to the work/arguments of these few scholars, without having more general validity. While I don’t think that this impression is really justified, it would certainly have helped a lot if Maier wouldn’t have chosen so polemic a language for his book. Last but not least–the book could be compressed to fill, say, 200-300 pages. It consists of 500.

To start with more specific issues: I like the definition of biodiversity that Maier formulates very much. According to him, biodiversity is the multiplicity of kinds within biotic or biota-encompassing categories. Such categories might be, e.g., species, genotypes, functions/traits, ecosystems. However, he completely dismisses any “add-on concepts” that are often used in the biodiversity literature, in the context of biodiversity measures, such as rarity, uniqueness and, above all, abundances. Prima facie, this seems right. In the end, when we consider diversity of kinds in a category, e.g., the diversity of species, it is not really relevant how many individuals of each species there are. However, a few days ago I attended a very interesting talk at my university by Jonathan M. Chase, who showed that abundances are quite important in practical applications. When measuring biodiversity we always rely on samples–to make sampling efficient, the inclusion of abundance and other non-core-biodiversity variables is crucial. In addition to his broad definition, Maier stresses that the kinds within a biodiversity category must be treated equally (egalitarianism) and as fungible (economists would prefer the term “substitutable”). Thus, he criticises various attempts to discriminate against, e.g., specific species as either “less important” or “alien”. This is, I think, an important point, particularly his criticism of the concept of invasive alien species. However, he seems to ignore that some species are less important in the long run, as their disappearance has no significant effects on the survival of other species, while others may “pull down” other species with them, too. It is, indeed, a main problem with Maier’s analysis that at first sight it seems very convincing, but later turns out to be too simplistic.

It would be too much to present all arguments Maier makes to show that biodiversity has no value. Instead, I would like to pick up three most common concepts of what constitutes biodiversity’s value, and critically analyse Maier’s respective criticism (in that, I will defend my own concept of biodiversity’s value, which I am currently developing as part of my PhD thesis). I will use his nomenclature for the concepts. Before I start, however, I would like to make one point that is relevant for all three lines of criticism. Interestingly, this is a point that Maier makes himself, but he downplays its importance and does not really take it into account most of the time. The point is the following: biodiversity as a concept is only relevant because our knowledge of the natural world is inherently limited. If our knowledge of the interactions and dynamics within and between ecosystems would be perfect, the concept of biodiversity would be useless. Let me explain this by use of an example: in the ecological literature, there is a discussion of “biodiversity effects” on ecosystem functioning, as opposed to “identity effects”. The former are effects attributed to (species, genetic…) diversity, the latter are attributed to specific species or genes or other individual entities. However, in reality all such effects are actually the result of either the “activities” of single species (or genes or whatever) or of interactions of a specific group of species. We just don’t understand them well, and if these interactions are complex, we are doomed to viewing them in terms of the crude notion of biodiversity. Now, if we could overcome the knowledge limitations we face, we wouldn’t any more have to resort to biodiversity, as we would now exactly which entities in the ecosystem are the relevant ones and what the relevant interactions look like. But we don’t know that, and this is, I believe, something we have to accept as permanent. Our knowledge is getting better and more precise all the time (although some argue that every question we succeed to answer creates new unsolved questions), but it will never be perfect. For this reason, I think that biodiversity will always be a relevant and helpful concept in ecology. Also, its thus understood nature–as reflecting our knowledge limitations–constitutes a major part of its value.

1. Biodiversity as Pharmacopoeia: one of the most common arguments used in favour of the thesis that biodiversity is valuable to people is that it is the source of new medicines. Also, the argument goes, pharmaceutical companies engage in bioprospecting, which means that they buy land or licences for specific use of this land, particularly in tropical forest areas, to search the flora and fauna for bioactive substances which might be the basis of new medicines. By this, they are supposed to express an economic valuation of biodiversity in these areas. Maier counters this argument by pointing out that, first, it is specific plants and animals which provide the substances we need to develop medicines, and second, there are only very few biota-based medicines on the market, most progress in this area being made via rational drug design. The latter argument seems to me convincing indeed. Bioprospecting is a seldom practice of rather minor importance, while rational drug design is quite efficient to date (and will likely become more so in the future). With regard to the former argument, it is exactly the kind of confusion I meant above–clearly, it is particular (groups of) plants and animals that provide us with pharmaceutically interesting bioactive substances. However, as we do not know which they are until we have found them, it is sensible to speak of them as contributing to the value of biodiversity. More on that below, under “Biodiversity Options”. However, taken together it seems that Maier is at least partly right–even if one grants biodiversity the role of the source of new medicines, it is not very valuable as such and likely not even indispensable due to rational drug design techniques. Furthermore, as he rightly points out, high levels of biodiversity are also linked to high levels of pathogen diversity–which means that, in terms of health, biodiversity might well be a nuisance for us. This is a point that rarely comes to surface in discussions of biodiversity’s value–rather, the focus is solely on biodiversity’s alleged potential to provide cures and suppress pathogens. Reality is indeed much more complex.
2. Biodiversity as Service Provider: another often-used argument for why biodiversity is valuable is that it underpins the (stability of) provision of ecosystem services. With regard to this line of thought, Maier questions the validity of the link between biodiversity and ecosystem functioning. Particularly, he rejects the extrapolation of small-scale experimental findings to ecosystems and points to the fact that some ecosystems exhibit exceptionally low levels of biodiversity, while being exceptionally stable and productive at the same time (his preferred example is salt marshes). Furthermore, Maier is no friend of the ecosystem services concept and argues that since most (provisioning and regulating) ecosystem services are dependent only on very few species, there is no logical connection between preserving ecosystem services on the one hand, and preserving biodiversity on the other. While there is some truth in each of the three arguments, they are all more or less flawed or at least one-sided when viewed from a broader perspective. It is a fact that the biodiversity-ecosystem functioning (BEF) debate is a complex and controversial one. And it does mainly depend on small-scale experiments. Still, state-of-the-art meta-analyses (e.g., this and that one) reveal that there is a general consensus, based on empirical data (both experimental and observational), that biodiversity and (stability of) ecosystem functioning correlate. More detailed effects are controversial, but the general message from this body of literature is rather unambiguous. With regard to his salt-marsh-argument, it is a clear misconception–no-one claims, to my knowledge at least, that more biodiverse ecosystems are per se more stable and productive. Rather, the BEF link is valid within a specific ecosystem type. You cannot compare completely different ecosystems and derive from that any conclusions about biodiversity effects. Last but not least, I think that Maier’s opposition to the ecosystem services concept is flawed for at least two reasons. First, he focuses entirely on provisioning and regulating services, and within the former class, mainly on agriculture, to argue that there is no need for much biodiversity to preserve them. However, he completely ignores the notion of cultural services, which may well have a more direct link to biodiversity. Further, he again downplays the limitations in our knowledge. Indeed, many provisioning and regulating ecosystem services depend directly only on a few species. Nevertheless, as we do not understand properly how ecosystems work and what the crucial interdependencies are, it might well be a good idea to preserve intact and biodiverse ecosystems if we want to ensure stable provision of ecosystem services. This is particularly true for regulating ecosystem services such as water purification.
3. Biodiversity Options: the last popular route of thinking about biodiversity value as criticised by Maier that I would like to discuss is the conviction that biodiversity bears options for the future–an idea borrowed by conservation biologists and environmentalists from economics. There are two variants of the value of options in economics, both discussed at length by Maier. Option value has its source in our risk-aversion–human-beings are generally rather cautious and welcome opportunities to “pool risks” (think of insurances or financial portfolios). Biodiversity is often seen as a kind of portfolio that carries options to react to future developments–indeed, the abovementioned pharmacopoeia argument is essentially an option-value argument. The other variant is called quasi-option value and is based on considerations of irreversibility: as we might in future realise that we need some parts of an ecosystem, there is a reason not to irreversibly alter it. Here, the link to biodiversity is less obvious, as quasi-option value is more about ecosystems as such, not just the diversity of their elements. Maier rightly points out that in discussions of biodiversity value these two strictly economic notions are invoked very carelessly. For example, one can only talk about quasi-option value when irreversibility is an issue. On the other hand, irreversibility is time-scale relative, and Maier seems to assume time-scales that are much longer than common in such discussions. Also, he attacks those who invoke option value as a source of biodiversity value for two main reasons, one of which is quite challenging for this line of argument, while the other is plainly wrong. The challenging argument is that the comparison of biodiversity with a financial portfolio has one major flaw: in a financial portfolio, all assets have a positive expected value. But not all species in the “biodiversity portfolio” do. For example, the already mentioned pathogens clearly have negative (expected) value, just as do agricultural pests. The strength of the portfolio approach in finance lies in the fact that, while fluctuating, the expected returns on all assets are positive. Otherwise they wouldn’t be included in the portfolio. However, there is no logical possibility of excluding the negatively valued “assets” from the biodiversity portfolio. This is indeed very challenging for the interpretation of biodiversity value as lying in its role as a “portfolio”. The other argument Maier uses is his questioning the general risk-aversion of human-beings. Meanwhile, it is a well-established fact that most people are risk-averse in most situations, as indicated for instance by the widespread purchases of insurances or the differences in rates of return on financial assets as depending on the respective risk of losses/defaults. Nonetheless, the portfolio-problem remains untouched by this and should be taken into account when one tries to make a case for biodiversity’s value resulting from its being a carrier of future options.

As can be seen from my responses to Maier’s arguments, the reasons for valuing biodiversity are clearly interlinked. And this fact provides the last argument against Maier that I would like to mention: he treats all the pro-biodiversity-value arguments as separate. But they aren’t. And taken together, they do show that biodiversity is valuable. On the other hand, Maier rightly points out that biodiversity is not all that is valuable in nature. But I would still claim that it is an important part.

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• biodiversity
• ecosystem services
• values