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Biodiversity - Week 3

Biodiversity: An Exploration

These pages are being generated as part of a senior seminar course directed by Neal Williams at Bryn Mawr College during fall semester, 2007 Among the topics to be considered are

  1. What is biodiversity?
  2. What's happening to biodiversity?
  3. Why is it happening?
  4. Why does it matter?
  5. What should/can be done about it?

This week, a discussion of

  • Purvis, A. and Hector (2000) Getting the Measure of Biodiversity. Nature 405: 212-219
  • Petchy, O.L. and Gaston, K.J. (2002) Extinction and the Loss of Functional Diversity. Proceedings of the Royal Society B 269: 1721-1727
  • Clough, Y. Holzschuh, A, Gabriel, D. Purtauf, T. Kleijn, D. Druess, A., Steffan-Dewenter, I., and Tscharntke, T. (2007) Alpha and Beta Diversity of Arthropods and Plants in Organically and Conventionally Managed Fields. Journal of Applied Ecology 44: 804-812
Background notes (Word document)
Williams17sept07.doc29 KB


Anne Dalke's picture

bio-diversity as human-centrity?

I'm dropping into this discussion from up the hill--over there in English House where cultural diversity is much discussed--and am intrigued. And puzzled. Once the goal of "genetic diversity" is re-defined as the aim of preserving as high a number as possible "of significant or meaningful experiences" ...

...then the whole game changes, right? Because the term "experience" has built into it--definitionally--consciousness, i.e. humanness? So then the goal of biodiversity gets re-defined as something that is human-centric, something that contributes to what humans value (the apples our grandfathers peeled for us, the grains our grandmothers baked with ...)? If only humans have 'experiences,' once "enhancing biodiversity" is defined as "adding to the sum total of 'meaningful experiences,'" then the only thing that counts is what humans count?

But mightn't there be a perspective available to us that doesn't measure value in human terms? Let me evoke an imaginative text: anyone else know James Tiptree/Alice Sheldon's sci fi short story, "The Last Flight of Doctor Ain," in which Dr. Ain infects all humans-->kills all order to save what he loves most: the planet Earth....?

Paul Grobstein's picture

Biodiversity as ongoing process rather than a definable state?

Lots of ideas in this discussion. A few things I want to think more about ...

Clearly "biodiversity" needs to be understood to be a term that has a variety of different meanings, ie its a "summary of observations" and one needs to be aware of/sensitive to the particular kind of observations being summarized in any given case. "Species richness" may be the most common/easy to measure meaning of "biodiversity" but it pays to keep in mind that demonstrably "the variety of life cannot be measured along a single dimension" (Purvis and Hector, 2000). Clearly, it is not only numbers of species but their relative frequencies and various additional idiosyncracies of species ("generalists" or "specialists"? their roles in larger communities?) that may be relevant in thinking about "biodiversity." There's an interesting parallel to this in thinking about grading in academic courses (cf end of Bio 103 course syllabus) , and in the problem of "assesment" in general, exemplified by, for example, the inability of a biologist to say which is the "best" organism.

"Unpeeling the onion" of "biodiversity" also calls attention to the phenomenon that different meanings both reflect and serve different objectives, and so inclines one to try and identify/unpack those. Is it actually "species richness" that one cares about, or is that simple a surrogate for the more important notion of "genetic" diversity? And, if so, why is one particularly concerned about specifically genetic diversity? And is that a concern about "life" in general or more specifically about human life?

Figure 2 of Purvis and Hector helps to bring out these issues. The total "genetic diversity" within fruit flies is, by a standard measure, greater than that of all monkeys, apes, and hominids. If one were committed to sustaining the maximal genetic diversity, one might therefore decide that preserving fruit flies takes precedence over sustaining primates (including humans). The twist here is that the standard measure of "genetic diversity" is based on the degree of differences in those parts of the genome which can reasonably have been presumed not to have been under selection pressure, ie those that have been varying randomly and so provide a good evolutionary clock. I though (and I suspect others) would be more inclined to use a measure of "genetic diversity" that emphasizes rather than downplays parts of the genome that have been under selection pressure, ie those that represent prior experiences rather than random change. Isn't it in some sense the total number of significant or meaningful "experiences" (how would one measure this?) that one wants to preserve, and so makes one concerned about a "biodiversity crisis" or "loss of the wild"?

If so, it seems to me one needs to acknowledge that the place of humans in evoution is less clear than it might normally appear. Yes, we are almost certainly responsible (as are other organisms) for the extinction of species and an associated loss of "biodiversity" in one sense But perhaps we (and other species) also enhance "biodiversity" in other senses, not ony be creating new kinds of ecological niches but also by adding to the sum total of "meaningful experiences" in other ways, represented not so much in genomes as in cultural embodiments?

Ought the issue perhaps be posed not so much in terms of "preserving" but rather in terms of "evolving"? Life was very good at generating new possibilities long before we existed, continues to be good at it, and will go on doing it whatever we do. Maybe what's important, both for humans and for life as a whole, isn't preserving "biodiversity" per se but rather finding ways that humans can be comfortable with and contribute to an ongoing process of generating biodiversity in the variety of known (and yet to be recognized) senses of that term?

Here too there are some interesting parallels to issues outside the strictly "biodiversity" realm. Languages, for example, are continually changing in ways that include extinctions (cf Languages Die, but Not Their Last Words) Might our thinking about biodiversity be useful in thinking about the problems and possibilities of cultural change, and those in turn contribute to our thinking about biodiversity?


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