Out of Eden

For those of you interested in invasive species, the NYTimes has an excerpt of the first chapter of Out of Eden: An Odyssey of Ecological Invasion. The book’s author, Alan Burdick, sums up the problem neatly: “The greatest threat to biological diversity is no longer just bulldozers or pesticides but, in a sense, nature itself.”

The NYTimes’s review illustrates the book’s engaging prose that epitomizes the best of science writing. However, the reviewer wonders if Burdick goes too far in trying to soften the blow of environmental disaster and ends up contradicting himself.

Burdick tries to make the case that nature is adaptable enough to handle the changes in our topsy-turvy world. When scientists figure out how to isolate the problem and interpret all the variables, it appears, for instance, that even having 500-pound feral pigs rooting through the forests of Hawaii may not do the permanent damage conservationists fear. Instead of causing local extinctions, he writes, “most successful invaders simply blend into the ecological woodwork. . . . To the local eye, biological diversity seems to have increased. Isn’t that a good thing?”

Maybe Burdick is simply trying to avoid the hazards of environmental alarmism, but surely this goes too far. It doesn’t square with the evidence he has diligently accumulated: What about the Australian tree spreading rapidly through the Everglades that ”draws in so much water through its roots that it essentially converts open marsh habitats . . . into . . . dry land”? What about the European green crab, which “single-leggedly crushed the soft-shell clam industry north of Cape Cod”? And how about, shortly after a cholera epidemic in South America in 1991, ships dumping ballast water that released the same strain of cholera bacteria into oyster beds at Mobile Bay in Alabama? The argument that many, or even most, invasive species cause no harm risks encouraging a “What, me worry?” attitude in a public already too complacent about environmental change.

In addition to worrying about complacency, this passage should cause us to question the use of increased biodiversity as a measure of environmental quality. Are more species in a habitat necessarily better? Of course not. Still, it’s easier to do counts than it is assess the more qualitative aspects of a habitat. This problem has been called the “meaning/measurement dilemma” by Warner (1967). That is, the value or meaning of the measure varies inversely with the objectivity of the measure. Both activists and policymakers attribute low meaning to objective—easily quantifiable—measures (e.g., the number of spotted owls); conversely, high-level meaning measures (for instance, biodiversity quality) are viewed as too subjective. So if we are to assess the long-term impacts of invasive species then we need good (and publicly digestible) measures of the effects.

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