Well rather than asserting that perhaps you can support it with some references? Are there any non-venomous snakes inhabiting areas without venomous snakes that use it?
Well we won’t get bogged down in the details. The point is that you conclude that many predators don’t strike without warning. That is all that is required for defensive venom to have a massive evolutionary advantage. That particular argument can now be scrapped since every snake in the world apparently has at leats one predtaor that doesn’t strike without warning.
Well then can we have a reference to support it please?
I’m not trying to imply anything. I am pointing out that if venom were to act as a major deterrent as you described it we would expect the non-venomous snakes to either become extinct or else to evolve methods to counter balance it. Those are the only two options. You can’t have a situation in the natural world where two direct competitor species are subject to massively different predation rates and both survive which is what you implied should happen.
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The evolution of predation defenses is an “evolutionary arms race” between the predator and the prey to continually “out-evolve” the other. This balances in the end due to the fact that neither ever gets to far ahead of the other.
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And yet you have suggested that “venom” as a “defensive advantage” would result in “the rates of predation of venomous snakes” being “significantly lower”. Why would it be significantly lower unless the prey species were significantly ahead of the predator?
A nonvenomous snake whose entire range is completely outside the range of any venomous snake? I can’t think of any snake off the top of my head that meet that criterion, let alone the type of their defensive display. Nearly all snakes utilize some kind of defensive display when cornered, and venom is “only” 60 milllion years old. What do you suppose snakes did before that? The fact that the trait is as cosmopolitan as it is suggests that it is rooted farther back in the evolution of snakes than than the advent of venom, and suggestsing that all nonvenomous snakes are mimicking venomous snakes is slightly ridiculous, akin to suggesting that possums mimic badgers when they are cornered.
A reference that a snake being held in the grip of a coyote’s jaws will likely die? I’m afraid I don’t have one.
I still don’t understand. I’m saying venom doesn’t act as a major deterrent; that venomous and nonvenomous snakes are subject to roughly equivalent forces of predation when they occupy similar niches. Cottonmouths and water snakes in the southeastern United States are similarly sized, have very similar habitats and are often found syntopically, and have similar diets. They are also equally preyed upon equally by alligators, snapping turtles, hawks, etc.
I’m saying that if venom were a significant defensive advantage, venomous snakes would be at the top of the food chain in much the same way that a tiger has no predators other than man because of its advantages of size, strength and lethality. Yet, venomous snakes are preyed upon; no less, apparently, because of their venom; indicating to me that venom does not confer a significant defense.
I can accept that. But unless the coyote is gripping the snake very near to its (the snake’s) head, wouldn’t the snake have a pretty good chance of killing the coyote, too? I know that if I had poisonous fangs, and a predator had me in its jaws and my death were certain, I’d try to bite and inject it. Yeah, the snake still dies, but that’s one coyote who’s inclined to nosh on snake who’s been removed from the gene pool, so at least I’ll make the world a slightly safer place for my offspring and other relatives.
And for the record, the plural of “mongoose” is “polygoose”.
Sure. It probably happens occasionally. But remember, this is a skilled predator, so the likelihood of a strike being possible are probably low and the coyote won’t necessarily die. Additionally, as Blake pointed out, if the snake has not been quickly dispatched it will have been exhausted and likely incapacitated before being eaten. If you’ve never seen a video of a large predator like an alligator or a coyote eating a snake, they grab it and shake it violently while biting hard. Lather, rinse, repeat until the animal can be safely consumed.
So there is no reason at all to assume it’s not essentially Batesian mimmicry.
Not specifically, simply a reference that a snake will lose an encounter with most predators most of the time.
Since you don’t have that your statement doesn’t make a lot of sense. Monarch butterflies lose most encounters with most predators that get a good grip on them, are you proposing that monarch poison offers no defensive advantage?
And I’m pointing out that your any claim that if venom worked as deterrent venomous snakes would be preyed upon much less doesn’t hold true. It could only possibly hold true if the non-venomous snakes were unable to evolve alternative defensive methods, in which case they would becomes extinct.
Just so we can discuss this sensibly, will you accept that a wildebeest has a defensive advantage over a springbok because of its size?
Not according to any dictionary I’ve ever seen. I assume that was a joke.
Other than the fact that it is absurd to assume that nearly every nonvenomous snake on the planet of every conceivable phylogenetic stripe is essentially imitating a venomous snake when it puts on a defensive display. When a robin begins thrashing wildly and screaming when someone approaches its nest, it is not imitating a Killdeer. It is a common behavior in birds.
Not most of the time period, most of the time when the predator actually has physically grasped the snake with the intent of killing it.
OK, I understand your point now. Yes, I will concede that a wildebeest’s size gives it an advantage, in terms of size. The nonvenomous snakes would only go extinct when there were nonvenomous snakes in the same niche to being with, however. This is sometimes the case, sometimes not. The cottonmouth has nonvenomous analogues. The copperhead, throughout most of it’s range, doesn’t. If venom were a deterrent, then yes, either water snakes would go extinct or continue evolving new defense mechanisms. However, we would still expect overall predation rates to differ markedly between the copperhead and the corn snake (snakes that are sympatric, but not in competition). Put another way, cheetahs and springboks are similar in size. Why are the predation rates by lions significantly higher on springboks than on cheetahs? Yet, many birds eat spiders and grasshoppers with the same gusto.
If venom is a predatory deterrent, it is a very poor one indeed. The predation on animals with specialized defences is usually restricted to specialized predators. Yet snakes, both venomous and nonvenomous, are the prey of some of the most generalized predators in existence.
PBS here recently had a show on venemous animals (perhaps what inspired this thread?), and they mentioned that there are only four known venomous mammals.
Of course, they mentioned the platypus (as someone did upthread there aways).
Because that way, it kills mice really fast, reducing the distance they can run away before they drop and increasing the chance that the snake will get to eat them. In many cases, the venom is also the beginning of the digestive process too.
The bearded lizard linked is the friendly (if not quite cuddly) Bearded Dragon (Pogona) of Australia, found in homes and pet shops throughout the U.S. (and, presumably, Australia).
The Mexican Beaded Lizard is a venomous lizard of Western North America. (The linked site uses the sloppy terminology of referring to these snakes and lizards as poisonous.)
(Several sites mention that the Beaded Lizard and Gila Monster are the only venomous lizards. Interestingly, they tend to support my founder effect hypothesis: they are both in the genus Heloderma; they have adjacent ranges; they have nearly identical eating habits; both store fat in their tails; and they both use venom defensively.)
Its hard to compare venom from landborne vs water borne animals. The aquatic venom has to be stronger, partly, because of dilution. Also prey has to be subdued immediately or it would be lost, as food, but still dead. The hunter would be eliminating its food source, and not eating. A downward spiral.
Slight hijack: There’s an australian mouse, mole, vole, rat, anyway, some sort of rodent that’s poisonous. Is it like the Komoto Dragons? or does it have true venom?
No that’s not right. Males of both the Tachyglossus (Australian) and Zaglossus (New Guinea) echidnas share the male platypus’ spur and gland, but the echidna glands are non-functional. Only the male platypus has a functional venom gland.
D’oh! You are correct. I inserted an “r” where it didn’t need to be, then looked up the wrong photo. That’ll teach me to do searches on common names…
Doesn’t really change what I said, though: given their environment, they still aren’t “stand-out” conspicuous the way many poisonous frogs and insects are.
Nope. Of pitohuis alone, there are at least four species, and there’s a whole other genus - Ifrita - which is toxic. It is also believed that the toxicity of these birds is not inherited, but most likely acquired via diet. See this article (originally posted by Colibri in this thread). In fact, there appear to be several other bird species which use some sort of noxious chemical as a defense, as noted in that article:
No it isn’t absurd in the least. If venomous snakes put on a display that deters predation precisely because they are venomous and since we have agreed that all non-venomous snakes hare habitat with venomous then it would in fact be absurd to suggest that it didn’t happen.
Two simple questions Isla:
Do monarch butterflies use their poison as an effective defence?
Do 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?
Once you’ve answered those questions I think it will be easy to show the flaw in your reasoning re snakes.
Why? We don’t expect overall predation rates to differ markedly between the springbok and the wildebeest after all.
Because there are far more springboks simply because there will, in any ecosystem, be more primary than secondary consumers. I don’t believe that lions do kill significantly more springboks than cheetahs relative to their abundance despite the differing defences of the species. And the same applies to venomous and non-venomous snakes. Relative to abundance the predation rate is the same.
Simply not true. A chameleon has a specialised defence and is preyed upon by every suitably sized generic predator in that environment. The same is true of a sloth or an opossum or a platypus or a skunk, all of which have specialised defences. There is no specialised skunk predator or specialised chameleon predator.
This seems suspiciously like a circular argument. The predation on animals with specialized defences is usually restricted to specialized predators and we know when a defence is specialised because it restricts predation to specialised predators.
Wow, really? Shows what I know about birds. And that I should stop posting things I hear in bars as facts.
It makes sense that birds have an easier time evolving venom glands. Being more closely related to dinosaurs and other reptiles. Or are they?
What’s also amazing is how people find out about these things. I mean, which sane person travels the jungle eating his way through the local bird fauna in order to see which ones are poisonous?
“Choke, gargle, choke. I found another one, hooray! What a great day for science! Choke, gargle!”
These birds don’t have venom glands though. As we sorted out above venom is something that’s injected. These birds are simply poisonous if eaten, although there is some evidence that their bites may be mildy venomous as well.
What these birds have are slightly modified oil glands that secrete poisons that the birds eat. You know how when you eat a lot of garlic your skin can smell of garlic for days afterwards as the ‘oils’ are secreted in through the sweat glands? Well these birds do basically the same thing except the skin secretes the poisons form the insects and frogs the birds eat.
Birds aren’t more closely related to dinos, they are a type of dino if that’s how you want to think of them. If you don’t then they are simply descendants of dinosaurs in much the same way that we are descendants of reptile like ancestors. Their closest living relatives are the crocodiles.
However that’s all fairly irrelevant since:
Jurassic Park aside there is no evidence for any venomous dinosaurs.
Even amongst the reptiles poison isn’t really very common as we discussed above. It’s not as though simply being a reptile predisposes an animals to evolving venom/poison.
