Words matter. More specifically, the conventional meaning ascribed to words matters. I have been struggling with this in the context of some Mexico research this week. As a neophyte to biogeography, I wanted to solicit feedback from sage readers on this blog more experienced than myself. So, basically…all of you!
Allow me to set the stage.
Let’s take the Sierra Madre de Chiapas. For those who are unfamiliar, this is a northwest–southeast trending mountain range in Mexico and Guatemala which, in the Mexican state of Chiapas, tightly parallels the Pacific Ocean. The ragged peaks tower dramatically above the narrow coastal plain. Some might argue that it’s the coolest mountain range in Mesoamerica…but that’s a subject for another post! For most of its length in Chiapas, the western foothills of the Sierra Madre de Chiapas are less than 30 km from the Pacific Coast. But the eastern slopes, which eventually drain into the Gulf of Mexico, lie closer to 300 km from the Gulf. To put it another way, in Chiapas, the Continental Divide runs along the spine of the Sierra Madre de Chiapas. Rainfall to the west of the crest drains into the Pacific, via a short and direct route. Rainfall to the east of the crest drains into the Gulf, via a long and circuitous route.
Now let’s say that a species (to keep things interesting, let’s make it an emerald-green snake) occurs on both the eastern and western slopes of the Sierra Madre de Chiapas. To clarify, I am not talking about occurrence records that lie just a few dozen meters northeast (toward the Gulf) from the crest of the mountains. I am talking about records that lie multiple km away from the line where precipitation drains into the Pacific instead of the Gulf.
So, here’s my question: can the geographic range of this species accurately be described as a “Pacific versant distribution”? Put another way…does the word “versant” refer to the set of points on a map where rainfall drains into a particular ocean? Or does it refer to the set of points on a map that are all closer, in Euclidean distance, to a particular ocean?
The motivation behind my question is as follows. It appears that authors have long been misusing the phrase “Pacific versant“ when describing the distribution of the species in question. However, I am looking for independent confirmation of this suspicion before I (gently) call attention to those presumed mistakes.
Please share your thoughts in the comments! And because this is a dry topic, here is a photo of the species that may have motivated this post.
Biology of Mexican Herps 
Good question! Since the word appears to reference the direction in which something slopes, I would not necessarily want to use “versant” to describe the slopes that lead to the Central Depression of Chiapas. Otherwise you also have “Pacific versant” (due to the direction they are facing) on the south side of the Northern Highlands of Chiapas. That’s why in some of our discussions I would try to use language like “interior slopes of the Sierra Madre del Sur de Chiapas” rather than reference the versant, which is not very informative in this context due to the presence of the Central Depression.
For those of you that do not know the region well, the Central Depression in Chiapas shares high similarity biogeographically to the Pacific slopes of the Sierra Madre del Sur de Chiapas. So if I was talking about the herp communities in the Central Depression, I might mention that it contains much of the Pacific versant fauna.
I’d like to hear more thoughts on the topic though!
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Thanks a bunch, Levi! That all makes good sense to me.
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We’ve adjusted herp.mx/tacana 🙂
All but maybe an handful of the records for B. bicolor in Chiapas fall on the Pacific versant – and those that don’t are a stones throw (<5km) from the continental divide.
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Cool, thank you! I have been learning a lot since digging back into this early last month.
I agree that many B. bicolor records in Chiapas fall on Pacific slopes. But based on the research I’ve done so far, in Chiapas roughly 40% of vouchered records for B. bicolor actually fall on interior slopes. That number is a bit fuzzy, though, because there are several old records with locality data so vague that I cannot yet confidently allocate the records to one versant or the other.
I also agree that nearly all B. bicolor records on interior slopes lie very close to the Continental Divide. But at least one record lies 10 km from the Continental Divide, which we published a few years back: http://mesoamericanherpetology.com/uploads/3/4/7/9/34798824/mh_3-4_clause_et_al.pdf
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The majority of records with real, verifiable locality information fall on the Pacific slopes. The old records are indeed vague, usually only containing parts of the multi-part name of an ejido or finca and often with “Google hits” in the form of a pueblo/locality on the Atlantic slope. But, if you check the databases leveraging INEGI’s data, you almost always find a smaller Pacific Slope locality with the same/similar name (and most always in the vicinity of known records with higher degrees of confidence). When HERP.MX’s Chris Grünwald was looking at ‘ornatus’ we concluded that there were very few that fell on the other side of the continental divide (including Levy’s animal at MZFC). On a related note, we interviewed locals in cloud forest around Siltepec, Motozintla, etc. without positive hits and left with the idea that bicolor/ornatus probably do not range onto the Atlantic versant beyond the first couple thousand meters of cloud forest creeping over the continental divide. While saying that it is 100% restricted to the Pacific versant isn’t completely accurate, it is a predominately Pacific versant snake.
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Thanks for sharing the information about your conversations with residents of interior-slope communities! That is quite interesting and useful. As I alluded to earlier, my collaborators and I have a number of unpublished interior-slope records for B. bicolor that refute the conventional wisdom of it being a predominantly Pacific versant snake in Chiapas, although I continue to agree with you that, based on the available data, it appears to rarely extend more than a few km from the Continental Divide on the interior slopes. This dialogue is convincing me of the importance of publishing our new data sooner rather than later, so thanks!
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That’s fantastic. Really anything on Chiapanecan vipers should be considered important and publishable. Do your unpublished B. bicolor match up with “ornatus” or did you get some SE of the Huixtla – Motozintla Rd?
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