pattern and ecology: Varanids

[mbayless]

Hi All,
The other day I was reviewing some Marine Biology materials - just to brush up on it for enjoyment, when I stumbled onto the following information:

Oceanic Islands By Nunn. Page 309:

Banded Iguana life in wet zone (Brachylopus fasciatus) vrs. crested iguana (B. vitiensis) more diffuse coloration adapted to life in dry zone w/more varied coloration.

Do this same pattern morphology and ecology work for Varanids as well as Fiji Iguanas? Is this banded phase (= wet zone) a trait more often seen in wet zone reptiles than the more diffuse pattern seen in drier climate regions for Fiji Iguana apply to monitors too?

V. dumerilii and V. rudicollis come to mind - as well as V. exanthematicus. How about V. salvator or V. bengalensis?

Thoughts? Ideas?
markb

[kap10cavy]

What about albigs? I see dark and light colored albigs.
I see spotted and striped. Does this have to do with locale and/or heat absorbtion?

Scott

[mbayless]

Hi Scott,
I see this too - albigularis can be found far far from water - banded, splotched, speckled types too - I posted the above as I am not sure if it applies to monitors or not?? Just throwing it out there for comment....sometimes I get too caught up in my own ideas about these animals = but unlike some people, I adapt and change the model according to new information - as a good student of Science (= knowledge) should...

As you have read Scott, for the all the info 'out there' on albigularis, what I have written leads to more questions, not less. :)

markb

[kap10cavy]

Well, hopefully I will never run out of questions. Learning new things about these critters is what makes it fun for me.
I want to know everything.
So far my best teachers have been my lizards not some silly scientist. hahaha
Once I think I am starting to figure them out, they do something to throw me a curve and wondering,"Now what?"
Aint they fun?

Scott

[treevaranus]

Hey Mark, good topic once again, I nearly missed this one.. glanced over it I suppose.

I think one must ask what factors would call for differentiation in patterning. I would have to say that foliage types/amount of shade would have great effects on patterning, and I suppose that when you think about it, 'wet' areas are typically more densely forested than dry area, having a greater diversity in foliage/trees/plants, as well as a substanitally greater amount of shade coverage.

I am not entirely familiar with the natural range of Bells Lace Monitors, but I believe they are a northern population- more heavily forested areas... I could be mistaken..

But we also see banded monitors in rather dry conditions as well- V. pilbarensis and V. glauerti come to mind with their contrasting tail banding.

Members of the V. prasinus comples vary a bit in pattern, some are 'banded', others have ocelli making up faint bands, others have random spotting(kordensis).

While I think that it is more involved than just 'dry' vs. 'wet' areas, I do think that patterning in many varanids is a result of the foliage and amounts of shade they live among, which like I said, are usually limeted by/determined by rainfall.

That is an interesting concept, and I suppose wouldn't be that difficult to research with some of the currently recognized variants of the prasinus group- correlating rainfall amounts to patterning. I think that such allopatric variants indigenous to small islands would be ideal for such a study, when compared to say, different populations of V. niloticus in west africa... Probably a bit more difficult to get accurate correlations between rainfall and exact localities in that situation.

While findings may never be conclusive, it could give us some more insight into any correlations between wetness and patterning... where we can then dive deeper into the idea. I will try to look into it.. Finding rainfall reports for some of the small islands that some of the V. prasinus group comes from is going to be tough...

Cheers Mark and Scott,

Bob

[mbayless]

Hi Scott and Bob,

Well this silly scientist first looks at the animals, then compares it with all the literature at his disposal - and compares the two - sometimes they agree entirely, other times not - and then I take sides with the monitor, for they will always be 1-2-3- steps ahead of us...and playing catch-up with them is fun!

I have been looking at V.varius pattern for awhile, and I have noted the banded/bels phase are inland forms, and coastal types hav the diffuse pattern = care to comment Sam? DK? Others? I do believe there is something to the validity of two distinct 'races'* of Lace Goanna - more study and time will tell.

*an antiquated political incorrect term nowadays...

markb

[Sam Sweet]

Once again, Mark, I think that the general answer to your question is no. Is that good enough? I'll try to post something later on the functions of color and pattern in monitors.

[Sam Sweet]

Animal coloration and patterning serves many functions. Only one of those is crypsis (= camouflage), the topic of the thread here. Like most other scleroglossan lizards, monitors do not use bright colors or conspicuous postures for transferring information to other individuals (as we often see in iguanid and agamid lizards or chamaeleons, for example), and so yes, maybe, crypsis may be the principal determinant of the colors and patterns we see among monitor species.

Just to get rid of a common misconception at the outset, the visible colors of reptiles have little to do with heat absorption. Heat is transferred in the near-infrared portion of the spectrum, and all reptile skin is black to infrared light. A lizard that is white under visible light is just as black in the infrared as is one that we perceive as black, so the whole "heat uptake" role for colors as viewed in visible light goes out the window.

This sidebar serves one directly relevant purpose, because it introduces the Big Idea that both "color" and "pattern" are relative concepts. Artists know this, but the rest of us can use a reminder. For example, what color is snow? It depends, doesn't it, on the type of light that a particular patch is reflecting -- in a painting you might need to represent snow as gray, or blue, or pink, whatever, according to the available light. Light passing through foliage has different spectral qualities than open sunlight, and light reflecting from the ground is different again when it meets the pale belly of a monitor lizard and reflects to your eyes. A round-bodied animal should be darkest on top and palest below, because this will compensate for variation in light intensity around the body and in that sense 'cancel out' the highlights and shadows we use as visual clues to roundness – this is an old idea known as countershading, whose crypsis value becomes clear if you paint up a model and then check it out turned upside down.

OK, the spectral quality of light out there affects how we perceive colors. But what are monitors hiding from? Mostly not from humans, but instead from other predatory mammals, and especially from birds. However, other animals don't see colors the same way that we do, so this complicates any simple analysis. For example, how can deer hunters wear bright orange vests? Easy -- deer see that wavelength as gray. On the other hand, deer can see farther into the ultraviolet than we can, and some hunters have finally learned that you shouldn't wash your camo jacket in detergents with 'whiteners' – those products make your clothes look brighter to you, but they also make your camo jacket stand out like a black-light poster to a deer!

So now we have two Big Ideas about color – first, that an animal's apparent color depends on the lighting conditions where it is, and second, that natural selection is going to adapt the colors of an animal to be least visible to its most important predators. Now, how about pattern?

Pattern refers to the mix of color schemes and the relative sizes and positions of pattern elements. Countershading is a simple pattern, and there are lots of others. For example, many animals employ 'disruptive coloration', which is usually a bar or spot of a dark color with a narrow, bright upper edge. If the rest of the animal is neutrally colored, this highlighted mark fools the observer's eye – it appears to be closer to the viewer than the rest of the animal does, and so disrupts the animal's outline and integrity as a single 'thing'. A similar trick seen in many forest monitors involves rounded bright spots on a dark background – under dim light these spots are also indistinct, but in a fleck of sunlight they 'jump forward', and can momentarily confuse the eye about where the animal's back actually is. This is a good way to have a hawk grab an inch short of a fleeing lizard, and of course the lizard that gets away breeds more than the one that didn't.

The third Big Idea about crypsis is that pattern and pattern elements appear differently at different distances – small spots, bands and details are sharp at close range, but blend together from a distance, while larger pattern elements may stand out at middle range but also blend together as the observer gets farther away. Again, natural selection is paying attention to making crypsis most effective at the average distance that the typical predator is likeliest to see the animal. This is obviously farther away, on average, in open country than in dense vegetation, and so forth.

We can put this stuff all together in a slightly different way, by asking at last what would be the most general definition of crypsis? According to John Endler, who has done much of the recent novel work on the topic, a cryptic animal is one that appears to be a *random sample of its background*, as seen under the lighting conditions where it occurs, by the predators that represent the greatest risks, at the average distance that those predators look for prey.

So anyway -- no, Mark – forest monitors are not more often banded than those from more open habitats. Different monitors have different color and pattern schemes, and these often vary between juveniles and adults as well. There are lots of reasons "why", and I've only scraped the surface here. It does not work to look at a posed picture, or at your captive in its weirdly-lighted cage and say "this is obvious and that is so". Humans have good eyesight and are especially good at pattern recognition, and unlike most predators we can set a plan: "I know what a V. salvadorii looks like and I am going out in the woods now to find some". Even with that, people who work with wild monitors know that they are hard as the dickens to see.

[mbayless]

Hi Sam,
Thats a good post - and I agree with much of it, and will have to read up on this John Endler fellow. I have a few books on crpysis and will look into it.

But with V. varius, the pattern of bels phase 'appears' to be a small regionally localized area - so is it genetic phenotypic chance 25%, 50%, 75% etc. or is there something to this bels phase population?

Yes, I agree crypsis is common in Varanus - the eye stripe tells us that - what about those few species that do not have an eye stripe? The eye stripe protects the animal via camouflage from the spotter being spotted...and how important the eye is to the animal - as we see in many insects, fishes, etc. where the eyes are protected by being more crpytic...aint Nature Wonderful...
cheers Sam,
markb

[kap10cavy]

That would explain the dogs problem in finding my escaped lizard.
Somehow, one of my bigger savs escaped and was found outside. The dog heard the movent in the bushes but couldn't see it. The poor dog was barking and sniffing around trying to figure out what it was smelling and hearing.
I didn't see the beast at first, I found it because it ran when I got close.
If it would have stayed still, we might not have e
have found it. It just couldn't resist chasing and eating the anoles that are all over the bushes.
It's amazing that a 3 foot plus lizard can just sit there and hide.

Scott

[mbayless]

Patience is a virtue, and stealth and camouflage is an advantage.... as we know/will know from the next iquada attack in the USA whenever it happens - they blend in, become invisible until they get you... it works well for the predator and the prey - much to your dogs excitement and frustration...
markb

[crocdoc]

Hi guys! Back from holidays.

In answer to the V varius questions, as mark said, the bells phase is normally found out west (although some are found near the coast in southern queensland). No one is sure of the genetics at this stage, but from what little I have gathered from captive crosses with normal phase lace monitors, it appears that it may be a dominant gene following the standard mendelian pattern.

I can say that the speckled normal phase lace monitors found up and down the coast in NSW disappear when in dappled light on the forest floor, as do diamond pythons found in the same habitat (which are also yellowish or whiteish spots on a dark background).

It's thought by some that the banded bells form may have some advantage in more open forests out west, where the light isn't dappled but where there larger, hard edged shadows. However, both phases are found there and it isn't exclusively bells phase territory.

[mbayless]

Hi DK,
Thank you for your post on V.varius - very interesting. Somewhere I remember seeing a paper about the intensity of light hitting a forest floor vrs canopy levels - I will have to go find it again, and see how it might fit in with V.varius dynamics - if it does apply?

Cheers DK,
markb

[kap10cavy]

Ok Mark, step up. hahahaha
Been awhile since you heard that huh?
I am waiting to see that pic of the tree running on the ground you mentioned before. I am sure Bob and others would love to see it too.
And onother thing. I have been searching everywhere online for different studies. All I can find are authors and subjects, no actual articles.
I wish I had time to go to Auburn University and go through what they have. I don't see my boss leting me have time off to go read about critters.
Can you paont me in the right direction?

Scott

[mbayless]

Hi Scott,
I remember it is cited in a paper about lights and terrarias, so it is probably in the many articles written by Gherman (or something like that spelling) on lights = I will have to go look for it now....
but be patient. I just refiled all the materials I used for my most recent project back into the files, where I hope they will remain buried, until needed again....now I am working on a survey of the Nile monitor complex....and back to my treatise on dragons once again.....all 300+ pages of it so far....and not even close to finished....Chapter 3-4 is on Giant Lizards: Chapter 3 discusses past giant Varanus, aka V. prisca, V. dirius, etc...and Chapter 4 discusses locality specific sightings and reports of such animals - laugh Sam laugh....I am not making an opinion of these reports, but merely reporting of them...and other anomalies as well.
markb

[infernalis]

Resurrecting another of Mark's threads.

well worth reading this one folks.

[Pirarucu]

Thanks for bringing these up Wayne.

[infernalis]

Now I understand why crocdoc said he missed Mark to me once in the past.

He sure had a way to get people to use that grey matter inside their skulls.

[crocdoc]

I miss conversations with Mark, but it's also kind of freaky to suddenly see a post by him after all of these years :)

[infernalis]

I miss conversations with Mark, but it's also kind of freaky to suddenly see a post by him after all of these years :)

I honestly feel I missed out on some wonderful conversation opportunities, these two threads were far too good to leave buried in the forum archives though.

The idea exchange was brilliant, I wish we could get some discussions like these going on here today.

[Pirarucu]

I miss conversations with Mark, but it's also kind of freaky to suddenly see a post by him after all of these years :)I thought the same at first..
I agree Wayne, I love reading these in depth conversations. There is so much we don't know about these animals.

[Gregg M]

I was shocked to see this thread. Kinda freaked me out too Dave... Mark was a very close, dear friend of mine and my buddy John Adragna. No one hade as much written literature on varanids and other retiles than Mark had. The dude was a serious goldmine of information. He was even working on his very own African Varanid book. He was also writting a book on cryptozoology. I actually have a rough copy.

I miss Mark a lot. I met Mark in person for the first time in 1993. What a character. Took him to Hooters as soon as he got off the plane. They made him stand on a table, put a tin bucket on his head, put a giant hotdog in his hand and made him dance to the weinie man song. LOL. So funny.

RIP buddy.