Biological Invasions: Economic and Environmental Costs of Alien Plant, Animal, and Microbe Species

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Ph.D., David Pimentel
CRC Press, Jun 13, 2002 - Nature - 384 pages
Bioinvasion is fast becoming one of the world's most costly ecological problems, as it disrupts agriculture, drastically alters ecosystems, spreads disease, and interferes with shipping. The economic and environmental damages from alien plant, animals, and microbes in the United States, British Isles, Australia, South Africa, India, and Brazil acco

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Full Disclosure: I am reviewing this book based on one excerpt from this book and the negative impact that it has had on the intellectual integrity of the discussion of feral cats and their impact on wildlife. Invasive species (which most certainly includes cats) is an important topic, so I hope Dr. Pimentel treats it with more care than he gave to his estimate of the economic impact of feral cat predation on wild birds. Dr. Pimentel attempts to monetize wild birds by assigning each bird a dollar value of $30. He arrives at this figure by throwing out three other, unrelated dollar values: 40 cents for each bird observed by a bird watcher; $216 for each bird killed by a hunter; and $800 for each bird reared by a specialist for release. He doesn't share the mathematical formula into which he presumably plugs these numbers to arrive at his result of $30, leaving us to speculate that perhaps the number 30 just felt right and was somewhere in between 40 cents and $216. The 40 cent per bird figure, calculated from data in a 1985 USFS recreation survey, is an utterly meaningless statistic. It takes all the money spent on bird related travel and bird related equipment and presumably spreads it over the number of birds estimated to be in the U.S. at any given time. What Dr. Pimentel either doesn't understand or chooses to ignore, is that bird related travel expenditures are highly disproportionately spent on specific bird watching areas and rare birds. For instance the 2004 Red-footed Falcon on Martha's Vineyard prompted hundreds of bird watchers to book flights, cars and hotel rooms, generating tens or hundreds of thousands of dollars in revenue. Averaging these dollars across every House Sparrow, Starling and Rock Pigeon is simply absurd.
Dr. Pimentel attempts to reinforce the $30 value by saying that the EPA values small fish and certainly a bird is worth three times a small fish. Apparently, his peers reviewing this work read this, nodded their heads and said "of course!" Why wouldn't a bird be worth just twice a small fish, or as much as four times a small fish? We are left to speculate. Again, this appears to just be a number that feels right to Dr. Pimentel. (By the way, that EPA value of a fish is based on fines that they issue, and fines don't actually correlate with the value of the object in question, just another lazy misstep.)
What is terribly unfortunate about this sloppy math is Dr. Pimentel quite possibly undervalues the real economic value of a bird. He most certainly undermines the ecological value of those birds who are unlikely to generate bird-related revenue. For example, a Cactus Wren facing diminishing numbers in a local ecosystem has far more ecological value than that misplaced Red-footed Falcon, but one would believe otherwise based on Dr. Pimentel's model.
Again, I dearly hope this sloppiness is an anomaly. If the bulk of Dr. Pimentel's figures are this random, then his book will unfortunately be of little value.

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