Killer Cactus?

For the discussion of topics related to the conservation, cultivation, propagation and exhibition of cacti & other succulents.
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graham
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Re: Killer Cactus?

Post by graham » Thu Sep 10, 2015 10:35 pm

I entirely agree with Dave's points, and, as he has pointed out, points that were being made from the outset, it's just very sad that 'survival of the fittest' caught on so well, but I suppose that 'non-survival of some of the less fit' doesn't really have the same impact.

It's also risky to make assumptions that any trait has an absolute advantage especially when there were no records kept at the time the trait was first observed and subsequently. Not only because inevitably, well, that's a bit risky in itself - so let's say 'in all likelihood' - the conditions when the trait was established were not the same as today.

As for predation, i.e. killing, as a anti-herbivore mechanism I have my doubts. It seems to be that there are several more effective ones: deterrence (i.e. sharp pointy things); bad taste (usually bitter, often alkaloids); hiding - very high often and so on. It's impossible to know how the proto-mammals behaved but whether rodents or ungulates and equids it's very likely that they had the vestiges of learned behaviour - from the mother, the family group or the herd - and in such a situation deterrence is a far more effective strategy: deter one, then another, then the offspring then the rest of the herd will avoid the plant, but killing means that the killed cannot pass on the "don't eat that plant" message.

Finally as for sheep-killing Puyas; I have to ask are there examples of the local camelids being killed ? Or the local rodents ? Or the native sheep ? Or is it just the bred for meat and wool essentially European sheep (also seemingly bred for lack of intelligence - or so some would claim) ?

graham
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Rogan
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Re: Killer Cactus?

Post by Rogan » Fri Sep 11, 2015 7:45 am

The answer: don't grow cactus - grow mesembs! :lol: :wink: :oops:
"Mesem-bri-la"
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IanW
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Re: Killer Cactus?

Post by IanW » Fri Sep 11, 2015 9:35 am

DaveW wrote:It is notable for places like coral reefs in warmer waters there is a greater bizarre range of variation between the fish species so the survival of the fittest is not so obvious compared to colder more stressful waters where variation in species becomes far less extreme and only the fittest shapes survive.
It doesn't matter if it's not obvious, that's a wholly anthropomorphic view- your premise is that if it's not obvious to a human what the benefit is, then the benefit doesn't exist, but that's nonsense, the universe doesn't revolve around humans. Just because we don't yet understand the survival benefits does not mean that they do not exist.
DaveW wrote:If we take Darwin's survival of the fittest to it's logical conclusion all habitats by now should be only populated by a single species, or at least all species having a similar form. That is patently not true since evolution only weeds out the unfittest which don't survive long enough to breed. It is surviving long enough to breed and passing on their genes that determines survival, anything non detrimental to that evolution ignores.
Again, complete nonsense, you're assuming that the duration of life on our planet is enough for convergence to reach a single point, you're assuming that everything works on human time scales, and if it's not done in our life time then it can't ever happen. We exist at a point in time, we're not the end game of the universe, we're not observing the universe at it's final ultimate stage.

But survival of the fittest doesn't preclude the possibility of multiple species in the long run regardless, species can happily both be fit, by complementing each other, often adapting together through coevolution.
DaveW wrote:If only the fittest were left and climate or conditions changed, as it has throughout the earths history, all life would be wiped out.
No, not all life, simply life that wasn't fit enough to adapt. This happens and is well documented, have you ever heard of the dinosaurs? Extinction events are a thing, but they don't require that everything dies off, just that which cannot adapt.
DaveW wrote:If you take the male birds of paradise for instance, producing long ornate plumes to attract the female prejudice's their flying ability and so makes them more vulnerable to predator's, but as long as the males last long enough to breed and pass on their genes the species survives.
Again, complete nonsense. You're assuming that such plumage has no defensive function in itself, and yet we know the many eyes display of species such as the Peacock is in itself a defensive mechanism. But even in reference to actual birds of paradise your theory is trivially dismissed by the fact that some such species don't have a rapid breeding cycle anyway - at least one species waits around 15 years before it first gets to breed which in itself is evidence of not having to select for predation risk, and instead having to select for simple ability to outcompete other members of their own species in an attempt to breed. Any species not well fitted to avoiding predators would be wiped out if there was a significant predation risk and average time to first breeding was 15 years - this would in itself require that evolution drive first breeding to a much younger age.
DaveW wrote:Evidently Wallace agreed with my emphasis above that evolution works by the elimination of the unfittest, leaving all those that can survive long enough to breed, not simply the single most fit, as the following quote shows
Why go all the way back to Darwin and Wallace? Neither of them really got it completely right even though they were obviously profoundly influential in kickstarting that area of human knowledge. We're 150 odd years on now and know much better than both of them put together about the topic.

You can't approach topics that examine the very nature of life and the universe with a wholly anthropomorphic view that the universe revolves around us and that everything must be obvious to us, and work on our time scales. It doesn't. We are not the centre of the universe.
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Re: Killer Cactus?

Post by IanW » Fri Sep 11, 2015 9:46 am

graham wrote:It's also risky to make assumptions that any trait has an absolute advantage especially when there were no records kept at the time the trait was first observed and subsequently. Not only because inevitably, well, that's a bit risky in itself - so let's say 'in all likelihood' - the conditions when the trait was established were not the same as today.
The problem is, if you believe this, then you need to find a compelling counter-explanation as to how the development of a new trait in one in maybe 10,000 members of a species becomes predominant. You need to explain why, no matter how many times you try, if you provide a population of a fast breeding species and genetically modify one of them with a trait offering no survival advantage that trait never becomes predominant, but if you add a mutation with a survival advantage then it often does - this is an actual experiment we can reproduce in labs, and if you have a compelling counter-explanation for it I'm sure the entirety of the scientific community would love to hear what you're proposing and I'd certainly find it interesting too.

Thus far, the only plausible explanation we have is survival of the fittest. If you want to disagree with the likeliness of that as a theory that's fine, but you need a more compelling argument than "I don't like/don't understand the implications of that theory and how it works so it's probably not true".

Emergence is a profoundly well studied field, with strong mathematical backing behind it, and survival of the fittest is merely a form of emergence.

So whilst yes, you may be right, survival of the fittest is wrong, but if you genuinely believe that I don't think you quite grasp the scale of the task you have ahead in proving your case - the body of evidence against is overwhelming, and that's why it's perceived to be by far the most credible explanation - there just isn't any other theory that can come close to the level of empirical and mathematical proof behind it.
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Re: Killer Cactus?

Post by Thermoman » Fri Sep 11, 2015 9:55 am

Whilst I would be one of the first to agree that 'survival of the fittest' does not imply that those who pump iron shall inherit the Earth, this is surely not the point. I posed and reposed a question with a binary answer which I still await. If 'don't know' is the only currently available response then should not the BCSS mount an expedition forthwith to settle the matter?
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Re: Killer Cactus?

Post by fruit » Fri Sep 11, 2015 10:00 am

Thermoman wrote:should not the BCSS mount an expedition forthwith to settle the matter?
There's no-one left, they've all gone to Belgium!
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Re: Killer Cactus?

Post by IanW » Fri Sep 11, 2015 10:01 am

If "don't know" is a possible outcome, then it's not a question with a binary answer is it? Any attempt at receiving a binary answer will merely ignore complexity of the topic and be largely worthless.

But if you want a binary answer that belies the complexity of the topic, then here it is: "No"
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Re: Killer Cactus?

Post by KarlR » Fri Sep 11, 2015 10:49 am

graham wrote:Finally as for sheep-killing Puyas; I have to ask are there examples of the local camelids being killed ? Or the local rodents ? Or the native sheep ? Or is it just the bred for meat and wool essentially European sheep (also seemingly bred for lack of intelligence - or so some would claim) ?
I have no idea. I don't even know how well documented it is that sheep are caught by the plant and, if so, whether this is ever intentional from the plant's point of view in terms of having developed a potential capacity to trap and kill animals to provide extra nutrients. I have read articles claiming it's the flower spikes that kill but this seems nonsensical. It must be the recurving spines on the leaves that catch the sheep (and possibly other animals).

What I would suggest though, is that cacti won't have developed hooked spines for no reason. They must serve some purpose, otherwise why not just stick with straight spines. Perhaps the ultimate goal is simply to function as a deterrent in the same way as straight spines. If so, it's possible that hooked spines offer some advantage in terms of protection over straight spines, although if they did one would sort of assume that more species would have hooked spines. After all, there aren't that many species with hooked spines. An interesting case is Mammillaria perezdelarosae and the form described as ssp. andersonii. The former has hooked spines while the latter (usually) doesn't. Apart from that I can't really tell them apart. Or take Ferocactus with some species like F. latispinus having powerful hooked spines, while others such as F. histrix are perfectly content with ordinary straight spines. It seems logical that there must be a reason for the spines being hooked or not.

As an aside, the Saguaro is known to have killed at least two people in the US. One was killed when, after having shot the poor plant full of bullets, it toppled over and crushed him. Another was killed when, after crashing his paraglider into one of the giant plants, it toppled over and killed him in the cockpit after the unfortunate pilot had initially survived the crash landing itself.
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Re: Killer Cactus?

Post by Thermoman » Fri Sep 11, 2015 11:23 am

IanW wrote:If "don't know" is a possible outcome, then it's not a question with a binary answer is it? Any attempt at receiving a binary answer will merely ignore complexity of the topic and be largely worthless.

But if you want a binary answer that belies the complexity of the topic, then here it is: "No"
There I must disagree with you. The question, “Are there disproportionately large quantities of small animal bones in the vicinity of hook-spined cacti in habit?” most certainly has a binary answer – 'Yes' or 'No'. 'Don't know' is not an answer. Complexity has nothing to do with it, any more than it has with the question of whether Freddie Starr ever ate someone's hamster.

If 'No' is your choice, is this based on field work? Have you, or some other trusted authority, actually counted animal bones around hook-spined cacti and compared the result with that around straight-spined plants? Were the results published?
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Re: Killer Cactus?

Post by Thermoman » Fri Sep 11, 2015 11:28 am

KarlR wrote:
graham wrote:...As an aside, the Saguaro is known to have killed at least two people in the US. One was killed when, after having shot the poor plant full of bullets, it toppled over and crushed him.
There does, then, appear to be some form of justice in the USA!
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