Conversations on Diversity Series Off to a Lively Start

The diversity of a particular habitat depends on the size
of the habitat, the immigration and emigration rates
of species, and the evolution and extinction rates of
species. (chart courtesy of Roger Lederer)
What constitutes diversity? How is it measured? How maintained? And what connections, if any, can we make between biological and cultural diversity?

These were some of the questions discussed during the Center for Multicultural and Gender Studies' first "Conversation on Diversity." Roger Lederer, a field biologist and dean of Natural Sciences, presented a talk entitled "Homage to Santa Rosalia, or Why Are There So Many Kinds of Animals?" from the classic paper by G. Evelyn Hutchinson, whose 1959 study of water-bugs in a Sicilian cave shrine led to the theory of biodiversity.

Lederer then fielded questions from the audience and participated in the discussion that followed.

When measuring biological diversity, Lederer explained, scientists must take into account not just the number of species but also their "equitability," or evenness of distribution. By the Shannon-Wiener biological diversity index, for instance, the Chico area measures out at around 1.0, fairly low when compared to the 4.0 of a tropical rainforest. Equatorial regions have a diversity advantage partly because they have been spared the catastrophic effects of glaciation, allowing them more time to develop new species.

Whatever the index, though, it's hard to know what parts or how much of a given environmental mosaic can be stressed or removed without causing the failure of the system overall.

Using a metronome and a pocket watch as metaphoric ecosystems, Lederer asked the participants to guess how much of each mechanism might be removed before it quit working. It turns out that removing six of the twelve parts of the metronome would not cause it to stop ticking, but taking away half of the 120 parts of the pocket watch would be ruinous. Of course, if you removed just one essential part of the metronome—the counterbalance, say—it, too, would cease operating. The parallel with natural systems seemed clear: take the kelp out of the Pacific or the ants out of the Amazon and the whole system collapses. Over time, Lederer said, diversity tends to peak, then fall off to about three-fourths of its highest level, where it then achieves stability.

Were there such a thing as a cultural diversity index, the Chico area would no doubt still yield a low number. Some might say that, culturally speaking, the catastrophic effects of glaciation still pertain. The question seems to be just how far the biological model can help us understand the cultural situation. After all, humans are all members of a single species (one that nevertheless shares 99 percent of its DNA with chimps). Given that, biologically speaking, the term "race" refers to regional differences, CMGS director Carol Burr asked whether it might be useful to consider some human "race" catastrophes, such as the forced passage of Africans to America, as regional disruptions. What might be learned?

In California, the uplift of the Sierra meant that magpies, originally a single species, developed into two distinct races: a black-billed type in the Susanville area and the yellow-billed race we find in the orchards around Chico. They don't communicate. Squirrels in Arizona that were divided by the Grand Canyon into the Kaibab race and a virtually identical cousin can no longer interbreed. In the 1800s, Lederer said, someone who believed America ought to contain all the birds of Shakespeare's plays brought over the first starlings, which thrived and quickly became pests. On the other hand, pheasants imported from China fit into the avian landscape without much of an impact.

The discussion ranged from the reintroduction of wolves in Yellowstone to miscegenation laws to the effects of population density versus the carrying capacity of the planet with almost everyone contributing a question or point of view. I left the gathering feeling a little more in touch with my inner chimp and looking forward to the next "Conversation on Diversity," when feminist philosopher Terri Elliot presents "Two White Girls Go for a Walk in the Dark."


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