Almost, but not quite.
Ilsa: You’ve been making quite a good argument against Batesian mimicry. Please check out this and re-arm yourself.
Blake: Occasionally you post useful things. But it seems to me that you started off in this thread by posting random nonsense:
Do you do this kind of thing deliberately? Just make stuff up as you go along? What’s the deal?
Man, all this argument about venoms as possible defensive adaptations and nobody mentions spitting cobras/rinkhals? What, are you all becoming old and slow and vulnerable to predation ;)?
Anyway that is one system that is undeniably a defense mechanism and a rather elaborate one at that. As to mimicry of venomous snakes being common, I think the coral snake controversy at least has been mostly laid to rest - it pretty likely is Batesian/Mullerian mimicry at work at some level. For example work in the 1970’s and 1990’s showed a strong tendency for avian predators to avoid models with coral snake patterns. See for example this review:
http://www.public.iastate.edu/~curteck/MIMICRY.PDF
- Tamerlane
Thank you Desmostylus; I already knew that, but the reference helps. The problem is that there are other venomous snakes in their ranges, just not coral snakes. I didn’t know what Blake would make of that.
FWIW, I am a herpetologist. I don’t have a PhD yet, I occasionally make mistakes, but I am published and generally know what I’m talking about RE: snakes (if little else!).
So: Tamerlane, you are correct. That is certainly a case of the secondary development of defense uses for venomous snakes. As for the coral snakes, the debate isn’t necessarily settled as to the reasons for the predator avoidance. I suspect that predators avoid them due to the fact that they have had bad experiences with bright colors in the past, i.e. monarchs and whatnot. The primary reason I don’t believe that it necessarily has anything to do with their venom is due to their behavior. Eastern coral snakes are nocturnal and fossorial. They are active mainly at night, and are hardly ever active on the surface. Additionally, they are very inoffensive animals. They are difficult to provoke. They also cannot really strike in the typical sense. They turn their head and jerk their upper body backwards towards whatever the threat is. They don’t strike in the traditional sense, and if grabbed near the rear portion of the body, they have trouble making contact. They do have tendency to flip wildly about after being provoked, though, this may be a deterrent to the predator.
Their colors do, however, do an excellent job of breaking up the line of their body as they dart away, making them difficult to follow. I suspect that this is their primary function, due to the secretive nature of the snakes in general. As to the predator avoidance, I am not convinced (nor are many of the herpetologists I know) that it is due primarily to their venom. The defenses of the supposed “mimics,” for instance, are radically different. The scarlet kingsnake (Lampropeltis triangulum elapsoides) begins, after being cornered, immediately attacking whatever has grasped it, biting and chewing (those little teeth hurt!). The scarlet snake (Cemophora coccinea) begins slowly writhing back and forth on the ground and autohemmorhaging from the mouth (quite disturbing). Combine this with the fact that almost the entire Lampropeltis triangulum complex (ranging across about 60% of the continental U.S.) shares the supposed mimicry pattern, while overlapping with the coral snake range in about 15% of it’s range, and the scarlet snake overlapping with the coral snake in about 30% of it’s range, and you begin to suspect claims of mimicry. All of these snakes are fossorial, however, and the pattern breaks up the line of their body when they are escaping. Avian predators may avoid them, but terrestrial predators like rats, raccoons and many other snakes don’t. I suspect that the pattern similarities are the result of some forces of convergent evolution for predator escape, rather than mimicry for predator avoidance.
As for the rest of the venomous snakes, yes, it is possible that their venom occasionally gives them some defensive advantage. This is, however, purely and distantly secondary, as evidenced by their reticence to even strike (as per the paper I linked) and their reticence to use venom when they strike. This, combined with the fact that venomous and nonvenomous snakes are eaten with gusto and little apparent regard for their toxicity by myriad predators, provides little evidence for their use of venom as a defense system. The idea that it is so effective as a defense that nonvenomous snakes are using Batesian mimicry to try to fool predators into believing they are venomous is ridiculous.
Desmpostylus I didn’t make up anything. Apparently you know nothing about scorpion fish
It is an ambush predator.
http://www.edge-of-reef.com/scorpenidi/SCOTaenianotustriacanthusen.htm
The style of lionfish predation, (i.e., ambush predator) is not unique on southeast United States reefs and wrecks (e.g., red grouper, frog fish, scorpion fish)…
www.public.iastate.edu/~zoogen/Bio394/394assn5.html
In short Desmostylus WTF are you on about? Whatever gives you the idea that scorpion fish are not ambush predators? That statement isn’t even vaguely controversial, much less made up.
Ilsa_Lund, I can’t help but notice that you refused to answer my two simple questions. Shall I take this as your acceptance that monarch butterflies do use their poison as an effective defence against predators despite the fact that monarchs lose an encounter with predators most of the time when the predator actually has physically grasped the butterfly with the intent of killing it?
Yes. This has exactly what to do with anything?
Well let’s see.
You said that defensive displays were a sign that venom has little or no defensive capability because
You then went on to further support that claim by saying that
You later qualified that by that you meant
But we know that the Monarch has a defensive display in its colouration. We know that any defensive advantage in the monarch is conferred only during a face-to-face encounter. We know that most of the time when the predator actually has physically grasped the monarch with the intent of killing it the monarch dies.
And yet for some reason you insist that poison is a defence for the monarch yet can’t possibly be for snakes because when a snake uses its poison for defence it dies.
And Isla can you please respond to my other questions and criticisms?
Why would we still expect overall predation rates to differ markedly between the copperhead and the corn snake when we don’t expect overall predation rates to differ markedly between the springbok and the wildebeest. You’ve already agreed that the wildebeest has a defensive advantage with no difference in predation. Why would that be different for snakes.
Do you have any evidence that ions kill significantly more springboks than cheetahs relative to their abundance?
Since you claimed that predation on animals with specialized defences is usually restricted to specialized predators can you name the specialised predators of platypus, skunks and chameleons?
To me it seems that all these claims are simply untrue. Since your argument hinges on such untrue statements that makes them relevant. And that is exactly what this has to do with everything.
Ilsa: Well, North American coral snakes are secretive and shy, 'tis true. But there are dozens of species of Micrurus ( as well as Micuroides and perhaps, if still recognized, a couple of Leptomicrurus ) in the Americas, many of them diurnal and many ready to bite defensively. As far as overlapping range, Harry Greene notes:
The evidence of harmless, brightly marked species in areas with no venomous models is not evidence against mimicry, since coral snake patterns might have arisen in a mimetic ancestor and been reatained for other ecological roles.
As you noted the rings are great camouflage on the forest floor ( which may play into the above statement ), but the fact that so many species use “self-mimicry” when threatened ( boldly displaying bright colors to ward off predation ), seems to indicate that those bright colors/patterns are used for more than merely passive defense.
As for a case of mere covergence…I dunno. Look at the photos in the back of Campbell and Lamar’s Venomous Reptiles of Latin America ( 1989, Cornell University Press ) some time - some of resemblances to sympatric coral snakes by “mimics” is simply astounding. As C & L point out, even a single species like Erthyrolamprus aesculapii can vary geographically to “mimic” whatever species of coral snakes happens to abound in a particular area - Micrurus hemprichii in eastern Colombia, Micrurus lemniscatus in Suriname, Micrurus spixii in southern Peru.
So put me down on the “pro-mimic” side :).
By the way I notice Greene cites Collared Peccaries and Coatimundis avoiding coral snake models as well, so it isn’t always just birds ( though given presumably weak mammalian color vision, one wonders if the pattern isn’t the key here, whereas in avian studies it definitely seems both color AND pattern related ).
- Tamerlane
In at least one case, it’s a narrowly targeted “overkill” – Australian red-back spiders are highly venomous to primates, but not particularly so to other large animals. There could have been no natural selection on this trait until very recently (there were no primates in Australia until the ancestors of the aborigines arrived about 40K years ago), and if anything it then became a slight evolutionary disadvantage (i.e. humans recognize, and go out of their way to kill, venomous spiders). This makes me think that it’s pure random accident of molecular configuration.
Correction: That should be “funnel-web” spider; red-backs are a different type of venomous Australian spider.
Fair enough. Don’t some of the Micruroides use the tail-as-head ploy, as well? WAG-territory: it may be that venom-as-defense is more common in elapids, due to them generally being more active, mobile and confrontational. That would explain the secondary evolution of the venom-related defenses of the spitters.
I’ll accept mimicry in the South American corals; I just don’t think that active mimicry explains the North American ‘mimics.’ They are probably related to the “other ecological roles.”
Ilsa I notice that you are ignoring my repeated requests for clarification and, you know, facts.
Do we take this to mean that you’ve got nothing?
Yes, this is one of several ways in which the dragons kill their prey. I’ve been to Komodo Island and seen the dragons at very close quarters. I learned a fair bit about them, from talking to the Guides and the villagers.
The dragons (giant lizards) are among the world’s greatest predators. Nothing can really harm a dragon except another dragon, whereas there’s virtually nothing a dragon can’t kill if it wants to. A dragon can run faster than the average dog if needs be. Younger ones can climb trees, older ones can’t but then again never need to. One well-aimed side-swipe of the very powerful tail will knock just about anything over and leave it feeling ‘dazed and confused’ to say the least, and probably will several broken bones. The dragon has extremely sharp, nasty claws that can rip anything open with one strike. Then, finally, there are the sharp teeth and the saliva that is effectively toxic and which contains anti-clotting bacteria.
To conserve energy, dragons wdo sometimes just bite their prey (small boar, deer etc.) and then allow the ‘toxic’ saliva to do its work and wait until the slowly-bleeding-to-death prey keels over. This usually takes hours rather than days. The dragon doesn’t worry about the prey trying to run or hide while it is bleeding from the wound, since the prey won’t get very far and in any case the dragon can ‘smell’ the blood from 2-3 miles away if needs be.
Grossly fallacious.
Snakes both venomous and nonvenomous, use the following as defenses:
In this order (roughly)
-
Fleeing
-
Coiling up, flattening the body, hissing.
3a) Gaping and fake striking.
or
3b)Coiling up tightly and hiding the head.
- Striking.
There are exceptions, such as feigning death, but this is what most snakes do. Even when physically molested and provoked to strike, venomous snakes are reticent to use their venom, as per the paper I linked and many, many other references.
When a predator has taken things to this level, a snake will likely lose. Even when a predator has taken things to this level, venomous snakes are unwilling to utilize venom in their defense. If venomous snakes used their venom as a defensive measure, we would expect them a) to stand their ground when attack and strike readily and often, while b) using their venom.
If venom constituted a major defensive advantage, we would expect two major things to be true: that a) the defensive strategies of venomous and nonvenomous snakes would differ (unless every snake everywhere was a Batesian mimic, which is unlikely), or at least would involve active defense with venom, rather than passive defense without it and b) that, even if nonvenomous snakes were Batesian mimics, for their predation rates to differ, as venomous snakes would be able to back up their bluffs with the ability to kill their attackers, as predators would learn to tell the difference between garter snakes and rattlesnakes fairly quickly. We would expect the rates to be different as nonvenomous snakes would not have access to as effective a defense strategy as their venomous counterparts. If venom were defensively advantageous, venomous snakes would not only have the options available to nonvenomous snakes, i.e. fleeing and bluffing, but also the added advatage of deadly toxins, just as the cheetah has it’s speed and jaws. We would expect predation on venomous snakes to be restricted to a few specialized predators capable of dealing with the difficulties of venom (and if widespread Batesian mimicry were the case, the predation of all snakes restricted to such) and not to any old opportunistic predator that hops through the forest.
I don’t know that ions kill many cheetahs or wildebeest. It appears that that was not a particularly apt analogy, however. Do lions kill many rhinos?
Prior to European settlement, platypi had relatively few terrestrial predators. Their primary predators are crocodiles. Although a few predators may occasionally take on a skunk, skunk predation is generally limited to owls and bobcats, the only animals generally tough enough to handle skunks. As for chameleons, their primary predators are the boomslang, vine snake and the Cuckoo hawk, a specialized chameleon predator.
Read the paper I linked. Although venom may occasionally constitute a small defensive advantage, it is not particularly effective as such, nor is that anything resembling its primary purpose, save a few isolated examples. This, as has been pointed out numerous times, is evidenced by the snake’s reluctance to use venom defensively, and the fact that they are preyed upon by a myriad of very generalized predators, as or nearly as often as their nonvenomous congeners.
No we wouldn’t, because as you already pointed out a snake in such a situation is likely to die. Natural selection would garauntee that this is exactly the behaviour we wouldn’t expect.
Do you actually have any figures on what proportion of venomous snakes actually inject venom in defensive strikes? I know that you have named one example, but we really need more than that.
And as I’ve pointed out its; highly unlikely that it would not be the case.
Really? Then would I be correct in saying that this argument hinges i their being no examples of where Batesian mimickry has resulted in identical predation rates?
Please answer so we can end this argument very quickly.
The problem is that it is as superbly apt analogy, one that you yourself could see was apt. With cheetahs and gazelle we have two creatures of the same approximate size living in the same environment with wildly differing defence mechanisms, both of which work. Yet the existence of that difference in defence mechanism hasn’t; resulted in differential predation.
I have no idea whether lions kill many rhinos. It’s rather a red herring. Nobody is saying that a perfectly effective defence has never been evolved. The point is that we can point to numerous examples of where moderately effective defences have evolved that have not resulted in differential predation rates. That makes a nonsense of your claim that if venom were a moderately effective defence we would expect differential predation rates.
Which doesn’t answer the question in any way at all. Are you saying that bobcats are specialised skunk predators? And that boomslangs are specialised chameleon predators? In what way are they specialised? What specialisations do they have for that prey type? It seems to me that these things are about as generic as predators can get.
What percentage of venomous snakes don’t inject any venom in defensive bites?
What, generalised predators like crocodiles, boomslangs and bobcats? But you just said that they were specialised predators didn’t you?
I am tiring rapidly of this discussion. You seem to be ignoring all of the major points I have made, instead choosing to pick nits with the minutiae.
Please outline precisely how you feel that venom constitutes a major defensive advantage for the majority of venomous snakes and why the predation rates are similar for both nonvenomous snakes and venomous snakes when they use the same defenses, which, for the venomous snakes, involve venom around 50% of the time.
Some food for thought:
http://jeb.biologists.org/cgi/content/full/204/24/24/e
That certainly seems to suggest the venom has a serious defensive role.
http://jeb.biologists.org/cgi/content/full/204/24/4345
Hmmm. That would certainly seem to suggest that defensive strikes are an effective defence, to the extent that they are using more venom.
http://www.umanitoba.ca/faculties/science/zoology/faculty/horn/z423/mimicry.ppt.
Double hmmm.
It certainly seems like the authorities are quite happy to accept that snake venom has a serious defensive role to play.
Nothing gives me the idea that they aren’t ambush predators. The statement is controversial, nonetheless. Let’s look at again:
What exactly is it hiding from? Hint: What does “ambush predator” mean? What would an ambush predator necessarily hide from?
Rubbish I have addressed every major point you have raised in detail. You on the other hand have to be badgered before you will answer even simple questions.
Well first off lets deal with facts, not fantasy. Venom is NOT used around 50% of the time. Even your own reference says venom may not be used in “as many as half of all bites”. IOW 50% is the lower end range. In fact “roughly 10 percent of the bites are dry” . That is nowhere around 50%. ( http://www.llu.edu/llu/grad/natsci/hayes/research-a-snake-venom/ ).
And that is for only one species
Next you should note that even some offensive bites are dry. If the presence of dry bites in a minority of cases is sign that the venom has no role to play in the effectiveness of the bite then you are presumably arguing that venom has no role to play o\in prey capture either. That’s clearly nonsense. The fact that a small minority of bites are dry clearly doesn’t signify much at all.
How is venom a major defensive advantage? Because venom kills predators or makes them ill. It works by exactly the same mechanisms that monarch \venom works by. I find it hard to believe that you can’t understand such a simple concept so I assume that wa sin fact a rhetorical question.
Why is predation the same on both venomous and non-venomous snakes? Through a combination of Batesian mimicry and the evolution of other defenses by non-venomous snakes. I have spelled this out in great detail previously.
Now will you please answer my questions, particularly given that I have provided references which state outright that snake venom plays a defensive role?