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October 10, 2006


wholesale perennials

Anyone who wants to grow healthy plants should know that location is one of the most important factors that governs successful growth of plants. Most people buy a plant, go out into the garden, dig a hole somewhere, and place the plant in the soil: and when the plant fails to grow, they blame the nursery or soil. Site selection is vital if you want your plants to grow and thrive. Choosing the best site can save a lot of frustration and headaches.


Ditto on Tim's last comment - I am still looking for a good companion reading for my students to pick apart alongside the chapters they are assigned out of the Theodoropoulos book. ;-)


Matt, I'd be very interested to see what you end up publishing. The social scientist in me is as interested in how the "second leading cause" idea became so entrenched as in the scientific reasons why it is not a valid statement.

Matt Chew

I presented a paper titled "The Invasion of the Second Greatest Threat" at the 2002 History of Science Society meeting.
It has been on hold ever since, while I researched and wrote my dissertation "Ending with Elton: Preludes to Invasion Biology," which discusses scientists' observations and conclusions regarding human redistribution of biota, beginning with Peter (Pehr) Kalm in 1749 and finishing with Charles Elton's 1958 book. I defended in November, and some publications will eventually emerge from that.
BUT, TO THE POINT: In 'Second Greatest Threat' I showed that E.O. Wilson's 1992 claim was based solely on cases from three papers about North American freshwater fishes, and that both his method and results were irreproducible. Furthermore, I showed that Wilcove, et al made virtually no attempt to separate quantitative studies from anecdote and opinion for their 1998 'BioScience' article (which also appeared, with significant rhetorical differences, as a chapter in the 2000 TNC book, 'Precious Heritage.' As has been pointed out already, the 'second greatest threat' claim has proliferated wildly, with no apparent restraint on either scientific or ethical grounds.
The problems with turning this sort of thing into a journal article are (a) many editors are unwilling to touch this sort of controversy, and (b) that the historians think it's biology while the biologists think it's history. And it takes awhile to really develop the narrative; the draft is 10K words in present form. But I hope to get it into the pipeline somewhere soon, now that the dissertation 'key log' has been worked free.


Rosie, I will concede the fine point but not the broad theme: namely, that the overall contribution of habitat destruction to the loss of federally endangered or threatened rare speces in ther United states is vastly greater than the next greatest threat posed by invasive species. Invasives are unquestionably significant, but on their own are a far distant second to habitat destruction. Invasives alter habitats: bulldozers and pavement eliminate them. Draining swamps has greater impacts overall on biodiversity than the simplification of native plant communities after invasion by invasive plants.

What irks me, and prompted this post, is not that invasive species are not a significant threat, but that the cavalier use of this one "statistic" mistates their impact, paints with too broad a brush -especially substituing "plants" for "species" - , and has been repeatedly uncritically restated to the point of meaningless.

Lab Lemming

Looking at biodiverity threats from an Australian/New Zealand POV, I would say that it is hard to overestimate the threat posed by introduced placental mammals. Or the cane toad.

And I seem to remember that a recent study showed that worldwide frog decline was caused by a disease carried by the invasive African clawed frog, and not by habitat destruction, as was previously believed. The internet gives me a popular article here:
But no link to the original journal article on which this is based.

Rosie Redfield

I think you may be misinterpreting the Simberloff quote. Saying that "habitat destruction contributes to the threat to 85 percent of all imperiled and federally listed species..." is not the same as saying that 85% of the threat is from habitat destruction.


In their massive publication, Threatened Birds of the World, BirdLife International places invasive species as the 3rd biggest threat to birds, impacting 25% of birds they categorize as at-risk globally. Habitat destruction is #1 (85% of species) and direct exploitation, mainly for food and cage birds, is #2 (31%; a species can have more than one threat).


Thanks, Jenn, for your - as always - informed and thoughtful perspective. Invasive organisms threaten biodiversity along with other things we humans value, such as rangeland, scenic vistas, our backyards. Allocating resources and policy to address these impacts is the overwhelming challenge, and in my experience, their being a leading cause of biodiversity is but one selling point for such efforts, and not always the primary motivator. The "nuisance factor" of acres of barberry, tangles of bittersweet, fouled boat propellors and dead trees blighted by introducted pests and pathogens motivates a broader swath of the population to deal this this problem.


Well, I certainly cannot argue with your statement that "second leading cause..." has become meaningless mantra. Really, it's just fodder for leading off any paper about invasive species, in that first paragraph where you're supposed to cite all the seminal papers so the reader can go back and consult them. I've seen people use this line and cite papers that are actually citing others, and I've seen people cite reviews as the source. I cringe every time I hear or read it.

However, there is at least one study that has come out over the past ten years that scientifically supports the statement: Wilcove et al. in Bioscience in 1998 ("Quantifying threats to imperiled species in the United States." - v. 48, pp. 607-615). I read it but darnit I cannot find a copy of it right now. It's got graphs and everything :-). That's the main one I see cited when writers choose to repeat the mantra - I don't really feel that the Davis paper referred to in that Science letter addressed Wilcove et al., and I don't remember seeing Matt Chew's "in press" paper he cites.

The other source I have seen is a bit vaguer - a book published in 2001, edited by Sala and Chapin, titled "Future scenarios global biodiversity." It was cited repeatedly while it was still in press. I have not read it so I am not sure what work was done and whether it was by the editors or by a chapter in the book authored by someone else.

I had never heard the idea that E.O. Wilson was behind the statement until I read your post.

Setting aside the difficulties in truly teasing apart habitat loss from invasive species (in many cases one can't happen without the other), I find that we've come up against that same problem we always do. Do we take a few decades to attempt to settle the argument or do we instead direct our resources to prevent further invasive species introductions? Maybe we can just all agree that invasive species is just one of several threats to native biodiversity.

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