The Lymnaeidae 2012: Tales from the cryptic stagnicolines

Editor's Note. This essay was subsequently published as Dillon, R.T., Jr. (2019b)  The Lymnaeidae 2012: Tales from the cryptic stagnicolines. pp 37-43 in The Freshwater Gastropods of North America Volume 2, Essays on the Pulmonates.  FWGNA Press, Charleston.

Kip Brady is a Teacher of Science at New Philadelphia High School in eastern Ohio, and an all around nice guy.  In 2008 he hooked up with our good friend Andy Turner of Clarion University, initially attracted by the potential of freshwater gastropods as tools for the classroom.  Soon Kip became involved with Andy on an NSF "Research Experience for Teachers" study of freshwater gastropods and leaf litter processing at the Pymatuning Laboratory of Ecology (1).

But their study involved several populations of dark, marsh-dwelling stagnicoline lymnaeids that have proven extremely difficult to identify (Above, 2).  The variety of Lymnaea elodes that Andy & Kip consider "typical" in NW Pennsylvania has a rather slender shell, with an estimated mean adult width: height ratio around 0.37.  But in Hartstown Marsh (east of Pymatuning Reservoir) they found a "robust" variety V2, demonstrating a mean adult shell W:L ratio around 0.44 (3).

Andy and Kip showed samples of these two varieties to me at the 2009 NABS meeting in Grand Rapids, but I'm afraid I wasn't much help.  The difference in the body whorl was more striking to my eye than the W:L ratio, but both shell types seemed within the normal range of variation one sees in populations called L. palustris in Europe or L. elodes here.  I suggested breeding studies, which in retrospect wasn't very practical advice.

So Kip decided to try a simple common garden experiment, carrying pure populations through multiple generations in a uniform environment.  He collected four populations of dark, marsh-dwelling lymnaeids from northwestern Pennsylvania differing in their W:L ratios, divided them into twelve 300-gallon cattle tanks, cultured them for three years, and re-examined the second generation born in the tanks.  While three of Kip's populations converged on a uniform shell morphology (Conley, Osgood, and Killbuck), the robust V2 population from Hartstown Marsh remained distinct (Below, 4).

Let's recap, shall we?  Had we asked Frank Collins Baker back in 1911 to estimate the number of stagnicoline species in North American waters, he would have suggested about 14 dark, skinny marsh-dwellers and 25 pale, fat river & lake dwellers.  But in 1951 Hubendick lumped all our dark/skinny marsh-dwellers under the European nomen L. palustris, and our pale/fat lake-dwellers under L. catascopium, with L. emarginata as a question mark (5).  Then in 1959, Maria Jackiewicz distinguished as many as five cryptic species under European L. palustris on anatomical grounds, one of which she described as L. occulta.  The range of that species (under the name L. terebra) has recently been shown to extend across the top of Europe and Asia to the Bering Land bridge.  And recent DNA sequence data reflect striking genetic similarity between an individual L. occulta/terebra sampled from Poland and individual L. elodes, L. emarginata, and L. catascopium sampled from Montana, Michigan, and Ontario (6).

Now comes the news that at least two cryptic species of dark/skinny marsh-dwelling stagnicolines are lurking in the marshes of Northwestern Pennsylvania.  Maybe this isn't news at all?  Maybe this is exactly what we should have expected had research in America kept pace with research in Europe?  Might one of Andy and Kip's varieties be L. palustris, as Hubendick suggested 60 years ago, and the other L. occulta/terebra?  If that's true, there must be twenty names here in North America, including elodes, catascopium and emarginata, that would have priority over the European nomina occulta and terebra.

So maybe F. C. Baker was right about the diversity of our stagnicoline fauna way back in 1911, and we should never have looked to Europe at all?  No, I don't think so. 

At left is a detail from Plate XXVI of Baker's 1911 monograph, showing shells he labeled "Galba palustris."  The similarity between this image and the photo above is striking, isn't it?  If you click the image you can see Baker's entire plate (7), showing shells from six populations of nominal G. palustris, numbered 17 - 37.  While most of the 21 shells depicted look like robust-V2 individuals, to my eye figures 17, 22, 23, 29, 33 and 35 appear to show typical-V1.  And figures 20, 26 and 34 are getting very close to L. catascopium, aren't they?  Many of Baker's other stagnicoline plates look similarly mixed, to my eye, including his plate XXXIV of "Galba" elodes.

Thumbing through the 162 pages of text and 18 plates that F. C. Baker dedicated to his 39 nominal species of stagnicolines, I just don't think we here in North America have ever caught a clue about the lymnaeid fauna that covers half our continent.

So now it's the 21st century.  Might modern DNA sequence data cast some light on this question?  Tune in next time...

Notes

(1) Brady, J. K & A. M. Turner (2010) Species-specific effects of gastropods on leaf litter processing in pond mesocosms.  Hydrobiologia 651: 93-100. [PDF available from Andy Turner's site].

(2) This montage made from photos kindly provided by Dr. Andy Turner.

(3) Statistical inference on ratios like this is real funky.  I understand that Andy & Kip are planning to re-run their analyses using ANCOVA.

(4) This image courtesy of Kip Brady.

(5) The Classification of the Lymnaeidae [28Dec06]

(6) The Lymnaeidae 2012: Tales of L. occulta [23Apr12]

(7) Plate XXVI from Baker (1911).  Figures 1 - 16 show L. haldemani, bulimoides, obrussa and petoskeyensis not important for our story.  Figures 17 - 37 are Galba palustris, with 17-20 from Alpena MI, 21-26 from Halma MN, 27-28 from Fort Erie NY, 29-32 from Charlotte NY, 33-34 from Ebenezer NY, and 35-37 from Windsor, ON.  Baker noted, "Figures 17 - 26 are excellent examples of spire variation."

The Lymnaeidae 2012: Tales of L. occulta

Editor's Note. This essay was subsequently published as Dillon, R.T., Jr. (2019b)  The Lymnaeidae 2012: Tales of L. occulta.  pp 29-35 in The Freshwater Gastropods of North America Volume 2, Essays on the Pulmonates.  FWGNA Press, Charleston.

We last reviewed the classification of the Lymnaeidae on 28Dec06 (1).  And faithful readers may remember that I am a big fan of Bengt Hubendick's 1951 work of genius, demonstrating that the worldwide Lymnaeidae "possesses great morphological uniformity, while there is a wide range of variation within the various species (2)."  Hubendick recognized about a dozen species in North America, which he saw no reason to subdivide (3), placing them all in the typical genus "Lymnaea."  Meanwhile other workers have continued to carry 50-60 North American lymnaeid species over from the era of Frank Collins Baker, recognizing as many as seven genera.  The system we have adopted for use in the FWGNA project is a compromise, accepting Hubendick's broad concept of the genus, while retaining the seven intermediate-level taxa as subgenera.

Has there been any progress since Hubendick?  The quick answer is yes, but not much here.

In a career spanning over 50 years, Poland's Maria Jackiewicz made a significant contribution to our understanding of the European Lymnaeidae (4).  And it materializes that the large, dark, marsh-dwelling populations which Hubendick lumped under the name "Lymnaea palustris" in Europe may comprise as many as five cryptic species, distinguishable by detail of reproductive morphology.  Jackiewicz rescued several names from synonymy under palustris and described one species afresh in 1959, "Galba" occulta (Figured above left, 5).  Her thinking on the higher classification of the Lymnaeidae has continued to evolve over the years, but as of 1998 she had three of these cryptic species (including palustris and occulta) in a subgenus Stagnicola and two of these species grouped with L. stagnalis in the (typical) subgenus Lymnaea (6).

In 2008 an important asterisk was added to the work of Jackiewicz by Vinarski & Gloer (7).  They demonstrated that populations previously referred to L. occulta in northern Europe range across Russia from the Baltic Sea to the Bering, and that the species seems to have first been described from Siberia as L. terebra (Westerlund, 1885).  All the way to the Bering land bridge, but not over it?  Indeed?

Meanwhile, back in North America, Hubendick was not able to distinguish any of our dozens of nominal species of dark, skinny, marsh-dwellers from European L. palustris either, but he did separate our pale, broadly-shelled inhabitants of exposed environments as either L. catascopium (Say 1817) or L. emarginata (Say 1821).  And H. J. Walter (1969) could not distinguish emarginata from catascopium (Right below, 9).  In an 102-page tour-de-force, Walter (8) disassembled a large sample of Michigan L. catascopium all the way down to the nuts and bolts, polished each part to a lustrous sheen, and re-assembled the whole into a sparkling wonderland of basommatophoran imagery. 

 

And in a brief sidebar that I think may prove stunningly prescient, Walter wrote, "A lymnaeid recently discovered in Poland, and described as a new species (Lymnaea occulta Jackiewicz, 1959), undoubtedly is of advanced stagnicoline character (like L. catascopium); one may suspect that it is an American species introduced into Europe."  So the pale, broadly-shelled, inhabitant of exposed environments we call L. catascopium here in North America is anatomically indistinguishable from the dark, slender-shelled inhabitant of marshes called L. occulta in Europe and L. tarebra across Siberia? Indeed?

But despite the contributions of H. J. Walter, research on the lymnaeid populations generally referred to Stagnicola (at the full genus rank) here in North America has, well, stagnated.  J. B. Burch reverted to the Baker system in his 1982 "North American Freshwater Snails," recognizing 5 nominal species in his dark-skinny "Stagnicola elodes group" and 16 nominal species in his pale-broad "Stagnicola catascopium/emarginata group (10)."  And that’s where we’ve sat for 30 years.

Which is not to say that no research has been published.  The first gene trees were constructed for the Lymnaeidae in 1997 by the North American researchers Remigio & Blair (11), and I’ve tossed at least twenty additional papers onto the stack with Remigio in the last 15 years, almost entirely European in origin, many of them execrable, beneath citation.  The phylogeny suggested by a gene tree is not a predictor variable; it is a response (12).  Do we know enough about the biology of the lymnaeid snails to make sense out of all the sequence data published in recent years by Remigio, Bargues, Mas-Coma, Pfenninger, Streit, Jarne, Pointier, and others?

We will address that question more fully in a future post.  But for now I will introduce just one little snippet from an ML tree based on a concatenation of 16s, ITS-1 and ITS-2 published by Correa and colleagues in 2010 (13).  The sequence divergence across all seven North American stagnicoline samples shown above - including Michigan elodes, catascopium and emarginata - is less than 5% (Click to see the whole tree).  And no more than a few percent distant from the North American stagnicolines is a sample of L. occulta from Poland (14).  Correa and colleagues hypothesized that "L. occulta was actually introduced in Europe from North American populations."  Indeed?

Notes

(1) The Classification of the Lymnaeidae [28Dec06]

(2) Hubendick, B. (1951)  Recent Lymnaeidae.  Their variation, morphology, taxonomy, nomenclature and distribution.  Kungliga Svenska Vetenskapsakademiens Handlingar Fjarde Serien 3: 1 - 223.

(3) Hubendick did consider the limpet-shaped North American taxon Lanx sufficiently distinct to warrant recognition at the genus level.  But Walter (Ref 8) wrote, "the limpet-like lymnaeids are more closely related to some species of "Stagnicola" than are some species of "Stagnicola" to each other, and therefore I must reject the taxa Lancinae and Lanx."

(4) Jackiewicz has probably published at least 10 -15 papers on the European stagnicolines in her career, but the most accessible to a North American audience is probably:

Jackiewicz, M. (1998)  European species of the family Lymnaeidae (Gastropoda, Pulmonata, Basommatophora).  This was published as a stand-alone volume of Biologica Silesiae, but is usually cited as a serial, Genus 9: 1 – 102.

(5) This photo was scanned from a useful handbook by Gloer & Meier-Brook (1994) Susswassermollusken.  Deutscher Jugendbund fur Naturbeobachtung. 136 pp.

(6) Jackiewicz has recently appeared as a coauthor on papers using the new lymnaeid genus "Catascopia."  See  Meier-Brook, C., & M. D. Bargues (2002)  Catascopia, a new genus for three Nearctic and one Palaearctic stagnicoline species (Gastropoda: Lymnaeidae).  Folia Malacologica 10: 83-84.

(7) Vinarksi, M. V. & P. Gloer (2008)  Taxonomic notes on Euro-Siberian freshwater molluscs.  3. Galba occulta Jackiewicz, 1959, is a junior synonym of Limnaea palustris var. terebra Westerlund, 1885.  Mollusca 26:175-185.  Can be downloaded from www.malaco.de here: [pdf]

(8) Walter, H. J. (1969) Illustrated biomorphology of the "angulata" lake form of the basommatophoran snail Lymnaea catascopium Say.  Malacological Review 2: 1 - 102.

(9) This specimen of L. catascopium was collected from Oneida Lake in upstate New York.

(10)  J. B. Burch's North American Freshwater Snails was first published in 1982 by the U.S. Environmental Protection Agency, then as a serial in the journal Walkerana, and then finally (1989) as a stand-alone book.  (Malacological Publications, Hamburg, MI).

(11) Remigio, E. A. & D. Blair (1997)  Molecular systematics of the freshwater snail family Lymnaeidae (Pulmonata: Basommatophora) utilising mitochondrial ribosomal DNA sequences .  J. Moll. Stud. 63: 173-185.

(12) Gene Trees and Species Trees [15July08]

But see "What is a Species Tree?" [12July11]

(13) Correa, A. C., J. S. Escobar, P. Durand, F. Renaud, P. David, P. Jarne, J-P Pointier, and S. Hurtrez-Bousses (2010)  Bridging gaps in the molecular phylogeny of the Lymnaeidae (Gastropoda: Pulmonata), vectors of fascioliasis.  BMC Evolutionary Biology 10: 381.  Open access here: [html]

(14) None of the eight sequences on this particular branch of the tree is original with Correa et al.  The North American sequences are from Remigio and the L. occulta sequence is from M. D. Bargues and colleagues.

Toward the Scientific Ranking of Conservation Status – Part III

Note: This essay was ultimately published as FWGNA Circular No. 1 (19Mar12).

Thank you all for your comments on my posts of December and January, regarding my new method for assigning conservation status ranks (1). Almost all of you addressed your emails to me personally, rather than posting comments to the blog. But I do think some of the points you raised are of sufficiently general interest to warrant sharing.

Many of you commented regarding the obvious sampling biases in the relative abundances of the freshwater gastropods listed on Table 1 in my January post (2). Here’s a cute example:

Maybe "commonness" is actually "commonly seen in the field without a microscope-ness." Large things (elephants, Oprah, etc.) tend to be noticed more than tiny things (hydrobiids, lawyer's souls, etc.)

Yes, I agree that the conservation ranks I suggested back in January do indeed reflect sampling biases against small-bodied species, and against species that are difficult to identify, and against species unusual or cryptic in their habitat.

My biological intuition suggests to me, for example, that the most common freshwater gastropod species in southern Atlantic drainages may actually be either Physa acuta or Ferrissia fragilis. The Physa abundances in Table 1 are certainly biased downward by taxonomic difficulties – several species (all common) cannot be distinguished as juveniles, and hence no Physa of any species can sometimes be tallied in samples where physids most certainly do occur. The abundance of the large-bodied Campeloma decisum was probably biased upward in the casually-collected samples we obtained from museums, and the small-bodied Ferrissia fragilis biased downward in the quantitative (or semi-quantitative) macrobenthic data we obtained from natural resource agencies. Limpets are rarely recovered from kick-samples.

But such routine sampling biases, irritating though they may be, are nevertheless random with respect to the object for which these data were tabulated. There is no reason to suspect that species warranting conservation concern are different in their body size, habitat choice, or taxonomic nuisance than more common species.

Much worse, from the standpoint of our purposes here, must be conservation-biased oversampling, the sampling error in favor of rare species generated as a consequence of the misbegotten system under which we currently labor. For today we first identify our putatively endangered species by pseudoscience, and then secondarily fund directed surveys to hunt that anointed subset specifically.

In the early 1980s, for example, Hugh Porter was funded by a North Carolina Wildlife Resources Commission grant to survey Lake Waccamaw (3). When I visited the NC Museum of Natural Sciences in 2005, there were so many lots of the (apparently endemic) Lake Waccamaw Floridobia (cataloged as "Cincinnatia sp."), differing only by transect number, that I simply closed the drawers and moved on (4). The (just 4) records of Waccamaw Floridobia shown in January Table 1 result from my own (arbitrary, but admittedly subjective) culling efforts.

Footnote #5 of my January post bears further attention in this regard. To compile my Table 1, I footnoted “We have screened any date-duplicates from the databases we have obtained from secondary sources, including museums and state natural resource agencies, as well as any nearly-neighboring collections, such as those taken upstream and downstream of single bridges.” This exercise was much more complex than my footnote made it sound, but was rendered necessary by overly-intensive sampling, often brought on by narrowly-directed surveys like Porter’s.

The situation regarding the endemic hydrobiid fauna of Georgia is similar. Fred Thompson has surveyed this fauna exhaustively, lodging in the Florida Museum of Natural History (for example) 49 records of Notogillia sathon and 29 records of Spilochlamys turgida from five small counties in central Georgia (5). Our colleague Charles Watson was also awarded a USFWS grant to survey this same fauna in 1995 (6), lodging 5 records of Notogillia and 4 records of Spilochlamys in the NCSM . These records I have boiled down to the 22 and 15 shown in Table 1, respectively, almost certainly every accessible spot where every Notogillia and Spilochlamys currently in existence can be sampled.

Meanwhile, January Table 1 showed just 16 records of Fontigens nickliniana, an ecologically-similar hydrobiid common in every hardwater spring in western Virginia (ranging all the way to Michigan, if you can believe it, Note 7) and hence attracting no interest from funding agencies or conservationists.

Io fluvialis must (literally) be the poster-child for conservation-biased oversampling (witness crawling to the left in the FMCS logo above). The snails are as spectacular on the hoof as any freshwater gastropod worldwide, but populations are currently restricted to the Clinch, Powell, Holston and Nolichucky Rivers in western Virginia and East Tennessee. The raw database I received in 2005 from Brian Watson, my colleague at the Virginia Fish & Game, included 128 (mostly historical) records of Io from Virginia alone, to which 54 records were added from directed surveys. I culled these records as best I could, but reference to the map at left (detail – click for larger) suggests that the 42 records ultimately remaining in our database continue to represent a gross over-estimate of the abundance of Io relative to the other 37 freshwater gastropods inhabiting East Tennessee River drainages.

The FWGNA survey we released in August found Pleurocera clavaeformis to be the most common freshwater gastropod in East Tennessee drainages, represented by 289 records as against our 42 records of Io. But my simple search of the Global Biodiversity Information Facility this morning returned 456 “occurrences” of Io fluvialis in the museums of the world, and just 204 occurrences of Pleurocera (“Elimia” or “Goniobasis”) clavaeformis (8).

So here’s my bottom line for the month of March. Not only is the method I proposed back in January scientific, it will be more effective in ranking species for conservation priority than the current system as developed by NatureServe. What is needed, now more than ever, is a continental survey of our freshwater gastropod fauna, conducted in a manner that is objective with respect to conservation status. Welcome to the FWGNA project… 14 years old, and still toddling forward (9).

Notes

(1) Toward the Scientific Ranking of Conservation Status:
Part I - [12Dec11]
Part II – [9Jan12]

(2) Table 1 - The 57 species of freshwater gastropods inhabiting the southern Atlantic drainages of the United States, ranked by their abundances in the FWGNA database 1/2012. [PDF]

(3) For references to Hugh Porter’s research see my post:
Crisis at Lake Waccamaw [16July10]

(4) My search of the online database at the NC Museum of Natural Sciences this morning only returned nine records of “Cincinnatia sp.” from Lake Waccamaw. That’s just a small fraction of their actual holdings, if my 2005 notes are correct. [NCSM]

(5) The Florida Museum of Natural History online database can be accessed here [FLMNH].

(6) Watson, C. (2000) Results of a survey for selected species of Hydrobiidae (Gastropoda) in Georgia and Florida. In Freshwater Mollusk Symposia Proceedings, Part II, eds. Tankersley, Warmolts, Watters, Armitage, Johnson & Butler, pp. 233 - 244. Columbus: Ohio Biological Survey.

(7) Hershler, R., Holsinger, J. & Hubricht, L. (1990) A revision of the North American freshwater snail genus Fontigens (Prosobranchia: Hydrobiidae). Smithsonian Contributions to Zoology, 509, 1-49.

(8) For more about the GBIF see:Freshwater Gastropod Databases Go Global! [26May09]

(9)  I initially made Parts I and II of this series available as a pdf separate back in January.  That document was updated on 19Mar2012 to FWGNA Circular No. 1.

The Peril of Clairvoyance in the Freshwater Gastropoda

I feel compelled to call the attention of our group to the video clip below, which aired on Comedy Central's "Colbert Report" 3Jan12, the night of the Iowa caucuses [1]. You may need to hit the "unmute" button at the lower right corner of the screen:

The Colbert Report
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So I gather that from an audience perspective, that was pretty funny. But was anybody thinking about the snail?

I am 95% sure that "Megyn Shelly," the brunt of the hilarity in Mr. Colbert's cruel prank, was a young adult Pomacea bridgesii [2] - the South American ampullariid that has risen to such popularity with aquarium hobbyists in recent years. I believe that's the variant with the albino body but pigmented shell [3].

So of course "Megyn" could not move when placed under the heat of Mr. Colbert's swirling spotlights - freshwater gastropods are notoriously immobile when suddenly transported into the terrestrial environment. In fact, she was holding her breath, fearing for her life. As Colbert and his heartless audience mocked and scorned! How could such a travesty be perpetrated?

I would speculate that Mr. Colbert suffers from a dearth of malacological expertise in his staff of comedy writers. So my guess would be, judging from the podia, that the part of Megyn Shelly was originally written for a land snail. And that only after plans were made, and cucumbers assembled, was some young intern tasked to call the local pet shops and audition a star for the show. On a short time line.

But I am not sure, even in New York City, that one can find a living land snail for pickup on short notice. Those things are pretty much all potential agricultural pests, every one of them, and the interest in the pet trade must be very close to negligible. One might order Helix aspersa from a biological supply company, but such an approach would have been no help to our young intern, who needed a star for the show that very evening.

So the talent agent at the pet shop on the other end of the telephone might well have responded to her renewed entreaties, "We've got some decent-sized aquarium snails we could sell you this afternoon." And by such a scenario, victimized by malacological fashion, USDA regulation, and cruel fate, I should speculate that our luckless ampullariid found herself dewatered on national television, to the general hilarity.

I know you read this blog, Colbert, and I have a prophecy for you. At the present writing (February 3) only four candidates remain in the running for the Republican presidential nomination. You endorsed Herman Cain right here on the CofC campus January 20, but Herman Cain endorsed Newt Gingrich eight days later. I predict this wave will carry Newt Gingrich to a victory in November.

A Gingrich presidency will cast a shadow over your rich, liberal, New York media establishment no different from the darkest hour of the McCarthy Era, Colbert! Megyn may have seen her low-water mark on your television show that fateful night of January 3. But you have seen your high.


Notes

[1] The clip can be viewed in a slightly larger format back at the Comedy Central mother ship here [Comedy Central].

[2] Is the common aquarium pet now being referred to P. diffusa? I saw an oral presentation from Ken Hayes at the AMS in July that suggested a huge amount of revision on the horizon for the Ampullariidae, including yet another name change for the invasive populations we're now calling P. insularum. But I haven't seen anything published since 2007. Have I missed a paper? Ken or Rob, would you care to enlighten us?

[3] There's a very nice website dedicated to apple snails in the aquarium run by a dedicated hobbyist named Stijn Ghesquiere here [applesnail.net]. The site features a cute (and credible) "hypothesis" regarding the genetic basis of the various color forms seen in P. bridgesii. But I do wish somebody would undertake a good, old-fashioned, Mendelian breeding study! And publish something formal.

Toward the Scientific Ranking of Conservation Status - Part II

Note: This essay was subsequently published as FWGNA Circular No. 1 (19Mar12).

Since the birth of their discipline, community ecologists have been interested in a phenomenon generally called “the distribution of commonness and rarity.” If one surveys bird abundance on a set of Pacific Islands, for example, certain patterns (e.g., all bird species equally common) do not seem to occur. Rather, what one typically finds is that a few species seem to be very common, and many species seem to be very rare. Such observations led to the development of several prominent theoretical models to explain the distribution of commonness and rarity, each based on slightly different assumptions about the processes that might be ordering biological communities. The best review of this literature I know is the 1975 work of Robert May [1].

The model that ultimately rose to prominence was the lognormal. In my book I gathered data from ten communities of freshwater mollusks (three of gastropods, five of unionid mussels, and two of pisidiid bivalves) and confirmed lognormal distributions for five of them, including the gastropod communities of Oneida Lake, NY, and Lake Esrom, Denmark [2].  A lognormal distribution of commonness and rarity is hypothesized to reflect “minimal structure” in biological communities [3]. If (for example) species #1 takes a random portion of the total resource, then species #2 takes a random portion of the remainder, then species #3 takes a random portion of the remainder, and so forth, a lognormal distribution of abundance will result.

Although (as far as I am aware) the lognormal model has not been extended beyond community ecology, it seems plausible to me that such “minimal structure” might generalize to evolutionary time, and find application to the regional (or even continental) distributions of related organisms no longer competing, or indeed even interacting, in any way.

For example, across the southern Atlantic drainages the FWGNA project has recorded 593 populations of Helisoma anceps and 192 populations of Helisoma trivolvis. But because H. trivolvis is adapted to lentic environments and H. anceps to lotic, they rarely occur together. The same relationship exists between Gyraulus parvus and Menetus dilatatus, and between Amnicola limosa and Somatogyrus virginicus, and in several other pairs and groups. This sort of “minimal structure,” integrated over the evolutionary history of the freshwater Gastropoda, might plausibly lead to a lognormal distribution of commonness and rarity at a scale much larger than the single biological community.

From the Atlantic drainages of the four southeastern states, the FWGNA Project has recorded the 57 species of freshwater gastropods ranked down the left margin of Table 1 [4] by the total number of lines in our database [5]. The most common species across the region was (somewhat surprisingly) Campeloma decisum with 1,188 records, followed by Physa acuta with 1,082 records, and so forth, down to four species (Gyraulus deflectus, Valvata tricarinata, Fontigens bottimeri and Marstonia gaddisorum) with one record each.

Because data of this sort are typically found to contain many singleton values, the convention in community ecology has been to use base-2 log transformation. Thus log2 abundances for all 57 species are given in Table 1 and plotted in Figure 1, to the left above [Note 6, click for larger].

A lognormal hypothesis does indeed fit the distribution of commonness and rarity of the 57 freshwater gastropod species of southern Atlantic drainages (Shapiro-Wilk W=0.962, p<0.065). The mean of the distribution shown in Figure 1 is 4.83 (= 28.4 records), with a standard deviation of 2.96 (= 7.8 records).

In recent years a widespread practice has developed wherein species are prioritized for conservation purposes into a system of five “status ranks” [See the previous post in this series – Note 7 below]. Convention would dictate that special consideration should be given to the rarest 5% of the species, 1.64 standard deviations (or more) below the log mean abundance. Shall we assign such especially-rare species to “Rank-5”? Then Rank-4 species might be those with log abundance less than 1.64 standard deviations below the mean but greater than 1 standard deviation, and Rank-3 species might be those between 1 standard deviation below the mean and the mean itself. Let us assign Rank-2 to species with log abundances greater than the mean but less than 1 standard deviation above, and Rank-1 to all species with log abundances greater than 1 standard deviation above the mean.

Figure 1 shows that the 57 freshwater gastropod species of southern Atlantic drainages include just the 4 singletons at Rank-5, an additional 7 species at Rank-4, 17 at Rank-3, 17 at Rank-2, and 12 species at Rank-1. The conservation ranks of all 57 species are given in the far right column of Table 1.

The implications of adopting such a system to guide conservation decisions more generally, in other groups of organisms elsewhere, would bear considerable discussion. Perhaps we will devote a third essay to this question in some future month. For now I will close with this.

It will be obvious to any of my readership with a general appreciation of the North American freshwater gastropod fauna that two of the four species here designated as “Rank-5” are narrowly endemic and genuinely rare (the two hydrobiids) and that two of the four species (Gyraulus deflectus and Valvata tricarinata) would have become much more common had our survey been extended further north. Clearly, the ranks we have assigned in the present exercise are dependent on the region surveyed. Thus we propose to call this set of 57 “FWGSA” ranks – Freshwater Gastropods of the Southern Atlantic drainages [8].
And more generally, the stability of any ranking system based on abundance data will be a function of the area surveyed – the smaller the area, the more unstable the classification. So although the regulatory apparatus for conservation purposes (and grant funding!) is largely administered by the states, we have resisted the temptation of calculating state-level abundance ranks here. Rather, we anticipate expanding our area of coverage, ultimately to include the entire continent, at which point we will publish FWGNA ranks, perhaps characterized by some stability.

But in any case, the system described above is rigorous, objective, and theoretically-based. In short, it is a scientific method to assign conservation status ranks, heaven help us.


Notes

[1] Although I dabbled in community ecology early in my career, I admit I have not kept up with the literature. There is probably something more current than this:
May, R. M. (1975) Patterns of species abundance and diversity. Pp. 81 – 120 in Ecology and Evolution of Communities (M. Cody and J. Diamond, eds). Cambridge, MA: Belknap Press.

[2] Pp 421 – 428 in Dillon, R. T., Jr. (2000) The Ecology of Freshwater Molluscs. Cambridge University Press. [website]

[3] Sugihara, G. (1980) Minimal community structure: An explanation of species abundance patterns. Am. Nat. 116: 770-787.

[4] Table 1. The 57 species of freshwater gastropods inhabiting the southern Atlantic drainages of the United States, ranked by their abundances in the FWGNA database 1/2012. [pdf]

[5] Each line in the FWGNA database records the collection of a single species at a discrete site. We have screened any date-duplicates from the databases we have obtained from secondary sources, including museums and state natural resource agencies, as well as any nearly-neighboring collections, such as those taken upstream and downstream of single bridges.

[6] Figure 1. Log2 abundances of the 57 freshwater gastropod species inhabiting the southern Atlantic drainages of the United States, divided into five categories (“FWGSA Ranks”) as described in text. [jpeg]

[7] Toward the Scientific Ranking of Conservation Status – Part I. [12Dec11]

[8] A paper including the text of both my December and January essays, together with Table 1 and Figure 1, was  initially made available as a pdf separate on 9Jan12.  That paper was updated on 19Mar12 as [FWGNA Circular No. 1].

Toward the Scientific Ranking of Conservation Status - Part I

Editor’s Note. This essay was originally published in FWGNA Circular No. 1 (19Mar12).  It was subsequently published as: Dillon, R.T., Jr. (2019d) Toward the scientific ranking of conservation status.  pp 223 - 227 in The Freshwater Gastropods of North America Volume 4, Essays on Ecology and Biogeography.  FWGNA Press, Charleston.

Last month I got an email from a colleague in the South Carolina Department of Natural Resources, asking for my help updating the state wildlife conservation plan. I told him I'd be willing to pitch in with the 2011-12 effort, just as I helped in 2004-05 [1]. But I continue to harbor deep misgivings about the entire process.

In Part I of the essay that follows, we debride a nasty sore on the left butt cheek of American environmental science - the unscientific (possibly pseudoscientific) method by which we prioritize our biota for conservation purposes. And in Part II of this series, to follow next month, we will begin the process of suturing that wound back up.

Like all other states with which I am familiar, South Carolina’s wildlife plan relies upon a subjective system of conservation status ranks, as follows:

S1 - Critically imperiled state-wide because of extreme rarity or because of some factor(s) making it especially vulnerable to extirpation.
S2 - Imperiled state-wide because of rarity or factor(s) making it vulnerable.
S3 - Rare or uncommon in state.
S4 - Apparently secure in state.
S5 - Demonstrably secure in state.

The spreadsheet my DNR colleague sent me for my input [2] had a column for species number (N=32 freshwater snails in South Carolina), scientific name, common name, legal status, conservation status rank (as above), and an (astonishing!) 19 additional data columns, more about which later. My colleague asked me to complete this massive 32x24 matrix by January 15, indicating as he did that the results would (ultimately) be forwarded onward to the nonprofit organization, NatureServe.

The origin and evolution of the conservation ranking system in general currency around the United States is shrouded in mystery. According to documents available from the NatureServe website [3], the notion of a state "natural heritage inventory" arose from collaboration between the nonprofit Nature Conservancy and my very own South Carolina back in 1974, with the first (A-B-C) system of conservation status ranking appearing in 1978. The current five-tier system was developed in 1982. In 1994 a group of state natural heritage program directors formed a related but independent nonprofit organization called the "Association for Biodiversity Information" to catalog the rising flood of inventory and status ranking data, which (in some complex fashion) led The Nature Conservancy to spin off "NatureServe" in 2001.

The 1982 system featured ranking at three scales: Global (G-ranks), National (N-ranks), and Sub-national (S-ranks), based on eight "factors" scored by anonymous participants. The number of factors taken into consideration has increased over the years, as has the number of participants, as has the elaboration of the technique by which the body of anonymous opinion is reputedly converted into a system of conservation status ranks.

For example, the 19 columns on the right side of the matrix my SCDNR colleague sent me last month included

• Knowledge of the species population status - "High" if we know the status throughout the species range, "Medium" if we know the status in select areas, "Low" if we know little to none.


• State Threats - "A" if very threatened, "B" if moderately threatened, "C" if not very threatened, "U" if unthreatened.


• Feasibility Measure - How likely is it that conservation activities can make a difference for this species (High, medium, low).

Any reader curious regarding the actual analytical technique by which standard international ignorance units (SIIUs), state threat quotients (STQs), feasibility metrics (FMs), and 16 similarly baffling variables counted and scored for each species are converted into the critical-imperilment-demonstrable-security scale on the global conservation status gauge is invited to peruse the voluminous documentation available from the NatureServe website [4].
This is obviously not science. Conservation status ranks, as they have been propagated throughout the entire natural resources community for 30 years, are not testable, verifiable or falsifiable. The entire system is, at its very foundation, anonymous, unaccountable, subjective opinion.

Are conservation status ranks merely unscientific, or are they pseudoscientific? Pseudoscience is “a claim, belief, or practice which is presented as scientific, but which does not adhere to a valid scientific method [5].” Thus the difference between harmless non-science and execrable pseudoscience is in its presentation.

To the extent that the conservation status ranks arising from this system are presented honestly, as an opinion poll of mysterious parameter, I think they can be excused as (at worst) innocent claptrap. Is there any better solution to the genuine challenge of prioritizing species for conservation? Are we not doing the best that we can in a difficult situation? This is America - take a vote. Fine.

But if there is any effort or intent to present conservation status ranks as scientific, then we as a community will be guilty of promulgating pseudoscience. The elaborate machinations of NatureServe, which have developed over the years into a byzantine system of coding and computation, look suspiciously like dressing a pig in a ball gown, especially when standing behind a velvet rope, looking towards the sty.

And when we scientists make use of conservation status ranks, we give the appearance of endorsing the process that brought them, turning nonscience into pseudoscience by the very act. Surely we wouldn't reproduce conservation status ranks in our peer-reviewed journals, would we? Surely, surely we scientists wouldn't gin up some "crisis" on the basis of such a system, in a self-serving ploy to attract funding for our own research programs, would we? To do so would be to commit pseudoscience of a high and aggravated nature.

I absolutely understand why natural resource agencies personnel rely on conservation status ranks for their state wildlife action plans. The state of South Carolina cannot launch inventories of every bug, slug, and butterfly within its vastly triangular borders every five years to meet the data requirements of each fresh wave of federal regulation [6].
But as scientists, we must be very clear that the current system of conservation status ranking, as implemented by NatureServe, cannot be endorsed.

The FWGNA project has now developed a large database with objective estimates of the abundance of all 57 species of freshwater snails inhabiting the Atlantic drainages of the southeast. In the next installment of this series, I will propose a new method to rank these 57 species into five categories of abundance for conservation purposes. But while this approach is designed to mimic the existing system of status ranking currently in favor throughout American conservation biology, it has a theoretical basis and will be rigorously objective.

Stay tuned...
Rob

Notes
[1] I reviewed the 2005 South Carolina wildlife plan together with the plans of nine other southeastern states in my essay, "Freshwater Gastropods in State Conservation Strategies - The South." [26May06]

[2] The header indicated that this particular data matrix has been developed in collaboration with North Carolina and Georgia. I was peripherally involved in the Virginia process back in 2004, and it wasn't quite as elaborate.

[3] See the brief history of NatureServe on its "Tenth Anniversary" page.
[4] NatureServe Conservation Status Assessments:
Methodology for Assigning Ranks

[5] This is from Wikipedia, which is the first hit one gets, if one googles it.

[6] I’m surrendering to reality here. In fact, the FWGNA has surveyed most of five states for less than $20k in total grant support. I suppose the entire country could be done for $200k. Land snails and bivalves for similar figures? Each order of insects? We’re probably talking several million dollars to inventory the biota of the entire country. I suppose that’s too much to ask.

The Freshwater Gastropods of Tennessee

The FWGNA project is pleased to announce the launch of our new web-based resource, "The Freshwater Gastropods of Tennessee," by R. T. Dillon and Martin Kohl. This brings to five the number of states currently covered by the project.

Our study area extends only over the eastern third of the state at the present time, to cover the Tennessee River and its tributaries upstream from the Alabama line just south of Chattanooga. But the area also includes 8 counties in southwest Virginia, 15 counties in western North Carolina, and 7 counties in north Georgia, for a total catchment of approximately 57,000 square kilometers.

A total of 38 freshwater gastropod species are documented from 766 sample sites, with distribution maps, taxonomic notes, a dichotomous key, a photo gallery, and conservation recommendations. Here’s the direct link:
The Freshwater Gastropods of Tennessee
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Pleurocerid snails often dominate the macrobenthos in this part of the world, especially in the smaller rivers and creeks that have escaped impoundment by the TVA. The spectacular morphological diversity demonstrated by the East Tennessee pleurocerid fauna led 19th-century authors to recognize at least 140 specific nomina, which Calvin Goodrich pared down to approximately 31 in 1940. Our review suggests that a better estimate of the biological species of pleurocerid snails inhabiting East Tennessee would be (a still impressive) 15.

Against this background, perhaps the most interesting finding of the present survey is the discovery of one valid biological species of pleurocerid snail that seems to have been entirely missed, in 200 years of shooting, 140 rounds fired. A formal description of this new "skinny simplex" species is currently in manuscript.
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Our appreciation is due (once again) to the Virginia Department of Game & Inland Fisheries for support of this work, as well as to the Office of Inventory and Monitoring at the Great Smoky Mountains National Park.