In the discussions and debates covered in my blog, buzzwords abound. Sustainability, capitalism, developed countries, consumer society, biodiversity… Because of the subject of my PhD thesis, I have had to deal with biodiversity the most recently. It is a great word, invoked by many in many different contexts and… lacking a specific, agreed upon definition. We love buzzwords, so we love biodiversity. The problem, however, with such words is that they hinder discussions, since everyone assumes that others understand it as one oneself does – which is not always the case. What is biodiversity?
The term biodiversity was created by the conservation biologist Walter Rosen in 1986. In this year, the National Forum on BioDiversity was held in Washington, the proceedings of which were published two years later in a book known to most ecologists – Biodiversity, edited by Edward O. Wilson. In its full form, biological diversity, the term was in use already in the 1970’s.
Many critics of the term have bemoaned that it has an emotional, advocative connotation. In an interview conducted by Edward Grumbine, the acknowledged population geneticist Michael Soulé said to the question why diversity is good that this is based on intuition and aesthetics, while admitting that an important goal of conservation biology is advocacy. On the other hand, biodiversity is believed to sound more “scientific” than the alternative nature, which is supposed to be one of the reasons why the term emerged at all. Whatever the exact motivation behind the coinage of the term, a widely recognized problem with biodiversity is that it has not a single, clear, agreed upon definition. It has been called pseudocognate, which means that its users implicitly assume that others understand it the same way as they themselves do. Also, biodiversity has been compared to love and faith as being a “fuzzy” term that is widely used even though there exists no clear definition of it.
The most popular and authoritative definition of biodiversity, however, is the definition of the Convention for Biological Diversity, which was one of the more tangible results of the Rio 1992 process:
“Biological diversity” means the variability among living organisms from all sources including, inter alia, terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are part: this includes diversity within species, between species and of ecosystems.
This definition has been replicated, partly in a slightly modified form, in many recent documents and analyses of biodiversity. Many definitions used have been even less specific, most of them stressing the variety aspect: “variety of morphology, behavior, physiology, and biochemistry in living things” (Mallett 1996), variety of life (DeLong 1996), “variety of life on Earth and […] its physical conditions” (Oksanen 2004), “the variety of life forms, the ecological roles they perform, and the genetic diversity they contain” (Wilcox, 1984). The vagueness of the CBD definition resembles the problems surrounding the Brundtland definition of sustainability.
Some commentators defend the use of such broad and inclusive definitions for pragmatic reasons. However, when it comes to more concrete aspects of the definition of biodiversity, there seem to be a number of points which biologists have not yet reached agreement on. For instance there exist controversies about whether biodiversity should only include biotic components of ecosystems or whether abiotic compartments should also be taken into account. Another point that has been frequently subject to debate is whether biodiversity should be only used in the context of “natural systems” or human-managed systems as well (particularly agriculture). The widely quoted CBD definition seems to include the latter. An interesting interpretation has been proposed where biodiversity is understood as information or insurance, the latter being an extension of the portfolio theory originating in financial economics, coupled with C.S. Holling’s notion of resilience. Both interpretations view biological diversity as something that provides a buffering service to ecosystems.
While the CBD definition only names three levels of biodiversity: intra-species (or genetic) diversity, inter-species (taxonomic and phylogenetic) diversity and ecosystems diversity, further (sub-)levels have been proposed, e.g. molecular biodiversity or the increasingly influential notion of functional diversity. Functional diversity seems to offer a particularly useful perspective, since it focuses on the functions fulfilled by the various parts of an ecosystems. However, variants of species diversity have been dominant in most analyses in the field, even though this particularly strong focus on species diversity have been criticized already in the 1980’s.
Biodiversity being such a “fuzzy” term, there is no easy way to quantify or operationalize it. It cannot be measured as such – only some of its aspects can. Two broad categories of biodiversity indicators can be found in the literature: those measuring numbers and those concentrating on differences, with a mixed category of indicators attempting to combine these two dimensions.
With regard to which aspect or level of biodiversity to measure, many different indicators have been proposed. The table depicted below provides an overview over the measures commonly used to express genetic, species and ecosystems diversity. According to some authors, genetic diversity is the most easily (or, rather, uncontroversially) operationalizable one since it deals with clear, countable entities. Species diversity is more complicated a measure, particularly due to a lack of agreement among biologists as to what constitutes a species, with ecosystems diversity being the most abstract notion.
|Level of diversity||Indicators|
|(Source: Nunes, Bergh, and Nijkamp 2003, modified)|
As can be seen in the table, most biodiversity indicators are nice in theory, but not easy to handle when it comes to empirical application, either due to lack of data or because the definitions of the indicators are too vague (e.g., what does “functional diversity differences mean?). Therefore, when it comes to actual application, e.g. in environmental economics, species diversity seems to be the variable of choice. Moreover, while it has been acknowledged that indicators of species diversity should include a notion of relatedness, this is a complicated matter in practice. As a group of economists pragmatically put it (Christie et al. 2007, 345–346):
Ecosystems are defined as communities of co-occurring species of plants and animals plus the physical environment; as such they are difficult to define and delimit. At the other end of the spectrum, genes are currently still difficult to identify and count. Thus, species counting is the obvious tool for measuring biodiversity.
Species richness has been called a suitable proxy for biodiversity and many researchers in the field of environmental or ecological economics seem to be implicitly following this conviction. A similar interpretation is reflected in measuring biodiversity changes in terms of species loss. The problem with this approach is, however, that to date only some 1.7 million species have been documented worldwide – meanwhile, estimates of their real numbers range from 10 to 100 million.
The sometimes misleading use of common indicators of biological diversity has been criticised, since they do not reflect links and interdependencies among species and may also invite to introduce non-native species as a move to enhance local biodiversity. In line with this critique, Partha Dasgupta stressed that biodiversity is about species that “have co-evolved under selection pressure [not] a simple head-count of “objects”” (Dasgupta 2004, 128).
The controversies surrounding the use of different and, at times, conflicting indicators of biodiversity, can be extended to the notion of biodiversity hotspots, proposed by Norman Myers. These are areas of outstanding, yet threatened biodiversity. Myers defined the hotspot areas based mainly on the vascular plant species diversity and endemism. Alternative defintions, based of different aspects of diversity, would be possible. While these likely wouldn’t change the general picture, it should be clear that there is some arbitrariness in Myers’s choice. Meanwhile, this arbitrary definition of biodiversity hotspots might determine the direction of resources aiming at the protection of natural systems. Whether the chosen hotspots are the most worthy of protection from the human perspective, is not clear.
The fact that there is no measure of “overall” biodiversity may be viewed as a sign of flexibility, not a problem. However, this supposed flexibility may lead to problems in conveying the message of biodiversity science, be it conservation biology, be it environmental economics or any other discipline dealing with this concept. If there are so many differing perspectives on what biodiversity is and how to measure it, transaction costs abound every time findings that depend on a particular approach have to be communicated. It should not be a surprise, then, that most people do not know what biodiversity is, and many researchers, particularly non-biologist, use the term as a true buzzword, a nice synonym of nature. So do the media. Meanwhile, whereas these terms are related, they do stress different aspects of the same reality.
This post is a modified section from my PhD thesis. I have omitted most citations. They can be provided upon request.