“All Life Ends! Amphibians, Cartilaginous Fishes Hardest Hit.”
That was the headline yesterday in newspapers all over the country as editors reacted to a press release from Science magazine which described a broad study of species loss. Even the Wall Street Journal, which is not known for overreacting, ran this: “A War Against Extinction: The Number of Species Keeps Falling, but Conservation Racks Up a Few Successes.” Golly! A war!
What makes this headline odd is that this same paper, and many others, not one month ago, announced to us: “Census of Marine Life unveils 6,000 new species.” That’s a lot of new species!
In an article announcing the many new species, the WSJ said:
Researchers participating in the census say they have now pinpointed about 250,000 species that live in the sea, but estimate that another 750,000 species still elude human discovery. And that’s without counting millions of microbe species, which constitute 90% of the ocean’s biomass.
So, which is it? Are the number of known species dwindling towards one (us, naturally), or are they proliferating out of control? The answer depends on what statistical method is used to count species. And in not making common errors the authors of the Science study appear to have made.
Suppose you have a list of Officially Tracked Species which are, obviously, known to you. There can be any number of species not known to you. At some point you go out in the field and try to count the number of each officially tracked species. Some time later, you venture out again and re-count. Only two things can happen: (1) the number of each species can go up or stay the same or (2) they can go down or become zero. But no matter what, the number of species on your official list can only decrease.
Why? Just think: your list of officially tracked species is set and, by definition, you are not adding to it. Your counting can only record extinction events. It is possible that since the official list was set, speciogenesis occurred somewhere, and we know with certainty that there are a large number of previously unknown species that could be added to the list. But the point is: these species are not on the list. So when you count, you can only be disappointed.
Thus, it should never shock a scientist to discover his list has shrunk. Poor Nicholas Dulvy, co-author to the Science study, evidently did not know this and was so upset after his counting that he fumed, “The reality is we’re still exporting degradation across the world.” See what I mean? Bad statistical thinking led US Citizen Dulvy to conjure up the image of his countrymen “exporting” some kind of species destruction engine.
The second error is this: the official list itself is incomplete. Dulvy and his brother scientists should have written an article announcing that the number of known species has increased since the last time they checked. And they should have acknowledged that it is likely to increase even further the next time. And they should have said that this will be so even if a few of the previously known species vanish.
Scientists do not have the power of King Herod and cannot order a census. They can only count a small sample, and are forced to use statistical modeling to estimate the extant number of any species. The models they use are error prone and cause over-certainty; and they often mistaken. How many times have we seen headlines like this? “‘Extinct’ Amphibians Rediscovered After Decades Lost to Science.” Amphibians! The very group said by Dulvy et alia to face the highest risk. Worse, as more people count, the bigger the chance that a species will be said to have gone extinct. (This is a form of observation bias.)
Now, it is true that some species since we have begun counting have gone extinct. This causes “biodiversity” to decrease, and that is said to be a bad thing. Sometimes, of course, the loss of a species is a bad thing. But not always. We can easily compile a list of killer microbes, creepy crawlys, and vermin that the world would be better off without. And what about the species thriving because of humanity? Dogs, cats, cows, pigs, and so forth are doing fine.
To say that some species are bad or good, or that some don’t count, or that diversity is important are moral judgments which have nothing to do with science.
Biodiversity is not to be desired just for the sake of diversity, either. Further, everybody believes this, even those who ever have that word on their lips. Prove it? Easily: suppose we create 10 new species, all of which are hostile or lethal to man. Biodiversity will have increased—hurrah!—but at the cost of human lives. Only the insane would say this is good.
Then, too, how many who worship biodiversity speak out against genetic modification of plants and animals, activities which can only increase, not decrease, diversity?