Wikipedia:Reference desk/Archives/Science/2018 March 12

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March 12

carnivore eats carnivore

Why do most carnivores prefer to eat herbivores and not other carnivores? Are herbivores tastier?2A02:8109:89C0:8AC:C40F:313C:7952:AC96 (talk) 15:42, 12 March 2018 (UTC)

That's an observation for mammals, but not fish. Anyone care to expand on that aspect? Andy Dingley (talk) 16:32, 12 March 2018 (UTC)

Even herbivorous can inflict life threatening injuries to a carnivore during the hunt (with horns and hoves). Should a carnivore animal pick a fight with another carnivore animal, neither is likely to come away uninjured. From a survival point of view, it is not worth the risk. Unless a big carnivore chances upon a small carnivore. In that case, carnivore do eat other carnivores. --Aspro (talk) 16:39, 12 March 2018 (UTC)

So it's only humans who do "Dog Eat Dog"?[1] ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:26, 12 March 2018 (UTC)

Dogs do, too. 2601:646:8E01:7E0B:0:0:0:64DA (talk) 06:37, 13 March 2018 (UTC)

(e/c)Herbivores are easier to catch and don't pose the same threat as another carnivore. I suspect they are tastier; perhaps someone who has eaten dog meat could confirm. Bushmeat is known to spread disease. Hyenas and vultures are not so fussy but they always let someone or something else do the killing.--Shantavira|^{feed me} 16:41, 12 March 2018 (UTC)

(edit conflict) Even among mammals, lions will predate the cubs of other big cats or of wild dogs if they have the opportunity. An apparent preference for berbivores may simply be because herbivores are (a) more common than carnivores and (b) don't have sharp teeth and claws. Gandalf61 (talk) 16:44, 12 March 2018 (UTC)

Trophic level. In particular the ten percent law says that 100 pounds of herbivore flesh only sustain 10 pounds of Level 2 carnivore and 1 pound of Level 3 carnivore. So, carnivore eating carnivores are rare, though certainly they make an impression. Note that cold-blooded animals are more efficient, hence more interesting chains among fish in the ocean. Wnt (talk) 17:59, 12 March 2018 (UTC)

This answer is so correct we could probably close the thread. To summarize a simply as possible (at the risk of imprecise phrasing): food energy derives from the sun, via plants. Plants use a portion of this energy to grow. Herbivores eat the plants and then use a portion of that energy to grow and/or live as well. Carnivores and carrion eaters eat herbivores and then use a portion of that energy to grow/live as well. Even if carnivores and carrion eaters were as easy to eat as herbivores (they almost are for modern human hunters), it's no where near as rewarding. Carnivores would have to be ten times easier to hunt just to be equally worthwhile. Cougars would have to be in the habit of breaking in to our houses and exploding into already butchered and cooked to be more useful than cows. Ian.thomson (talk) 18:19, 12 March 2018 (UTC)

Err, no, a cougar is likely about as nutritious as a herbivore of the same mass. The problem is that in order to "keep" a cougar, you need to provide it with ten times its weight in herbivores, and in that case you get 10x more food if you just eat the herbivores yourself. 93.136.99.236 (talk) 21:26, 12 March 2018 (UTC)

What’s the err bit for? The above doesn’t suggest that carnivore meat (like cougar) is more nutritious . Carnivorous are just further up the food chain. --Aspro (talk) 21:50, 12 March 2018 (UTC)

"Carnivores would have to be ten times easier to hunt just to be equally worthwhile." - this is the part that I disagreed with, that to me implies that carnivore meat is 10x less nutritious. That's not the issue (and probably not the reality, although we humans mostly dislike land carnivore meat for some reason) - the issue is that if you're a level 3 carnivore, you have to wait for your prey to feed and grow, and you use up a much higher share of the ecosystem in doing so than if you were level 2. That means that the ecosystem can support 10x smaller population of your species (going with the 10x estimate). If your species can also eat herbivores, it will be able to support a larger population than that, but that doesn't say anything about the nutriotiousness of carnivore meals. 93.136.99.236 (talk) 00:06, 13 March 2018 (UTC)

There is no rule or system other than big eats small aka Opportunism for carnivores. For example Sperm whales only eat squids, who are also carnivores and even often cannibalistic. Most seals eat fish, sea lions even specialize on penguins and sea birds and are themselves hunted by Sharks and Killer whale. Only the offspring is typically spared by its own parents and species. --Kharon (talk) 21:28, 12 March 2018 (UTC)

I think 93.136.99.236 is on-target here, and Ian and Wnt, generally reliable contributors, have missed the boat on this one. As 93 alludes to, the ultimate energy cost of the meat is a consideration for a rancher, but is unlikely to interest a predator.

It does seem plausible, though, that predators might avoid prey higher in the food chain to avoid higher concentrations of toxic substances; see biomagnification. From "plausible" to "true" is a big leap, and I don't know whether there is any good research on it. --Trovatore (talk) 21:40, 12 March 2018 (UTC)

A relevant question may be: what is the earliest carnivorous life on earth? Another relevant question may be: what is the earliest herbivorous life on earth? And a third relevant question concerns the truth or falsity of the hypothesis that most carnivores eat herbivores. If we know that herbivores preceded carnivores in the evolution of life on Earth, and if it is the case that most carnivores eat herbivores, then the reason for the present arrangement can be a consequence of the order in which the two types of life forms came into existence on Earth. Bus stop (talk) 22:38, 12 March 2018 (UTC)

@Trovatore: At no point did I suggest that carnivore meat is more nutritious. My point is 1) you need 100 pounds of herbivore meat to keep 10 pounds of carnivore meat living, if it feeds on herbivores, and 2) you need 10 pounds of carnivore meat to keep 1 pound of carnivore-eating carnivore meat living. Which means that if all sizes are equal, you expect to find 100 herbivores roaming around for every 10 carnivores that kill herbivores and every 1 carnivore that kills carnivores. Now to dispel an idea someone started pursuing above, this does not mean that purely carnivore-killing carnivores can't exist; they do because they have a distinct ecological niche, which means, if there are sufficiently few of them on a frontier, they can eat well because not much else could compete with them to eat those particular carnivores that are their prey, guaranteeing some equilibrium number can exist. Wnt (talk) 00:02, 13 March 2018 (UTC)

I think the question does not concern ecological niche. Sure there can be exceptions. But generally speaking, does most life on Earth follow the principle of carnivore eats herbivore? An ecological niche can be an exception to what generally is the case. Bus stop (talk) 00:10, 13 March 2018 (UTC)

By "ecological niche" I mean that you can always support a certain number of mongooses in their natural habitat, because nobody and nothing else is crazy enough to mess with a cobra. (* this is not really altogether true, but amusing) Wnt (talk) 00:19, 13 March 2018 (UTC)

And cobras are carnivores. But perhaps this arrangement is an exception to a general principle prevailing over the entirety of life forms on Earth. Bus stop (talk) 00:27, 13 March 2018 (UTC)

Well, eating carnivores has a higher ultimate energy cost, but the point is that the predator doesn't pay that cost. It's a pure externality. So you seem to have a missing step in your argument, if you claim that's the reason that predators prey less on animals higher on the food chain.

You might be just saying there are fewer of them around to eat? --Trovatore (talk) 00:29, 13 March 2018 (UTC)

The "balance of power" between herbivores and carnivores is a result of an as yet unidentified factor. I am suggesting a ratio of available nutritional value is a consequence of the order that these two classes of life came into existence. The first carnivores fed on herbivores, assuming that is the order in which they came into existence. I am suggesting that from that earlier point in time to the present, that ratio has been resistant to drastic change. Bus stop (talk) 00:42, 13 March 2018 (UTC)

The above was actually a response to Wnt. --Trovatore (talk) 00:49, 13 March 2018 (UTC)

I know it. I'm just trying to clarify my hypothesis. Bus stop (talk) 00:57, 13 March 2018 (UTC)

Yes, I was just saying there were fewer around to eat, and explaining the reason for that.

As for the "order of the two classes of life", that's basically balderdash. Sure, there's a "Carnivora", but in general there are a lot of omnivores and the ecology is relatively labile. As a generalization, mammals all pretty much look and act like rats (well, shrews if you want to use the favored description of the common ancestor), and will typically go back and forth from devouring grain, grasshoppers, or misfortunate fellow mammals pretty freely. Out of that, on occasion, some have developed more predictable tendencies, sometimes (as with panda bears) not what you'd expect. Wnt (talk) 02:09, 13 March 2018 (UTC)

How does one intelligently respond to the question "Why do most carnivores prefer to eat herbivores and not other carnivores? Are herbivores tastier?" So far, I don't see any answer emerging from the responses. At least, we should be intelligent enough to ask the relevant questions. Are the inbuilt assumptions correct? Do most carnivores eat herbivores? Bus stop (talk) 03:05, 13 March 2018 (UTC)

They have to, because about 90% of the available meat is herbivore, as I explained above. Wnt (talk) 21:59, 13 March 2018 (UTC)

@Wnt: As I understood the question, the claim is that predators selectively prefer herbivore meat. If that is true (I don't know whether it is), then saying there's more herbivore meat around is not really an answer.

It could be part of an answer, if you claim that the predators have to make specializations to eat one or the other, so it makes more sense to eat the one there's more of. But that's a separate claim that needs to be separately asserted and defended. Without it, the claim about prevalence is kind of a non sequitur. --Trovatore (talk) 17:50, 14 March 2018 (UTC)

Perhaps I took for granted that predators would occupy some knowable position in a food chain, yes. A hypothetical predator (Pac-Man) that can catch and devour any flesh the same way should have no preference. But if a predator needs to have any adaptation to catch specific prey, then for every one predator specialist there will be ten herbivore specialists ... provided the chances of catching and eating the food are the same, which admittedly I don't know. Even at the cultural level we tend to specialize -- there are some people who like to go out and hunt bear year after year, but most people choose deer because there are more of them. And people who regularly hunt deer wouldn't quite know how to hunt or cook a bear, so given one bullet and a choice, you might expect them to look for more deer. Wnt (talk) 19:02, 14 March 2018 (UTC)

Apart from the 90% of meat locked up in herbivores as Wnt points out, there is also the animal physiology to deal with. predators have evolved to kill, they have sharp teeth and claws, while herbivores have evolved to only prevent themselves from being eaten, but that hasn't led to a body design that's very lethal to predators. Herbivores have not evolved to be stronger or to be able to outrun predators either. Many herbivores have instead evolved to live in large herds and they are then protected by being safe in numbers. Basically the herd gives predators that hunt them what they want so that the vast majority of the herd members will survive. Evolution of the herbivores due to the pressure of predation is then driven more by competition within the herd than by competition between the herbivores and predators. A herd member is safe as long has it is not the slowest of the group, there is no need to be faster or stronger than the predator. Count Iblis (talk) 22:52, 13 March 2018 (UTC)

I suspect, but cannot prove, there is more to it than this. I have the impression that any herbivorous species like the dodo in the absence of predators will tend to degenerate, so that contrasted with another species subject to predators it has no chance to survive, and so in that sense the predator and prey are essentially symbiotic -- at the species level, that is. In the case of the dodo, of course, predators can be blamed for their demise, but I do wonder if an object lesson can be found where an herbivore literally became extinct through the lack of predation and ordinary levels of environmental change. Wnt (talk) 23:15, 13 March 2018 (UTC)

So the answer to the question originally posed is: availability, or as Trovatore said, "You might be just saying there are fewer of them around to eat?" Bus stop (talk) 23:11, 13 March 2018 (UTC)

See where I said "Yes", above. Wnt (talk) 23:16, 13 March 2018 (UTC)

OK, I stand corrected. Bus stop (talk) 00:36, 14 March 2018 (UTC)

'Degenerate' is a weird word to use in evolutionary contexts. NZ had very few mammals and no real land mammalian predators [2] (also earlier article). There were a small number of bird predators like the Haast's eagle and Ruru (Morepork) but on the whole, it's probably fair to say there were far few predators of larger animals than in many other locations. Species in NZ therefore evolved in this relatively predator free environment and many birds for example spend a lot of time on the ground with a number being completely flightless. With the introduction of mammalian predators particularly rats, ferrets, stoats, cats, dogs and for some humans (I mean as direct predators); many of animals have problems coping. Habitat and other largely human induced changes don't help either. This shouldn't be that surprising with a basic understanding of evolution. But how would these species compete in a pristine NZ (including fauna) with other herbivore birds etc. Some like rabbits would I suspect do well, probably even in a pristine NZ. But will all do so? BTW, in terms of the general question, I think this is one (of many) cases where we have to be careful about just so stories or simplistic answers. There's a reasonable chance a number of different factors in combination (albeit often related) have given rise to the rarity of carnivorous predation of other carnivores. I'd note also that many or even probably most predatory animals seem willing to be scavengers when the opportunity arises, as far as I know there's no evidence of much bias against scavenging other carnivores. I think even the bias again their own species tends to be a lot less than most people expect. Nil Einne (talk) 10:09, 15 March 2018 (UTC)

Y-chromosome inference

To what extent and with how much confidence can a man's Y chromosome be reconstructed, if only his daughters' and their mothers' genomes and biographies are available? 73.15.177.153 (talk) 21:58, 12 March 2018 (UTC)

According to Y chromosome, "95% of the human Y chromosome is unable to recombine", meaning that at most 5% of genetic material from the man's Y-chromosome can find its way into his daughters' genome. Even if this happens (and the change of it happening increases with the number of daughters), it is impossible to say whether any such material originating from the father comes from his Y-chromosome or from his X-chromosome. So in conclusion, I'd say that you can at most reconstruct 5% of the Y-chromosome, and your confidence is low, unless perhaps the probability of recombination is well known and there are lots of daughters for statistics. - Lindert (talk) 22:27, 12 March 2018 (UTC)

Well, if you can do a complete gene sequence of the pseudoautosomal region of both the mother and a daughter, then you should be able to identify regions of sequence that are, in their entirety, from the man, and can be used to identify the man from a sufficiently large and detailed database of the sort that you pretty much know that spies have probably amassed by now in secret. Crossovers in the pseudoautosomal region are actually obligatory [3] and hence such sequence should nearly always be available. That paper describes 220 single nucleotide polymorphisms in the region; the data seems to be available here. Wnt (talk) 00:18, 13 March 2018 (UTC)

Oh, whoops ... that answer conflicted with the premise that only those genomes were available. Without other data, it is possible to identify which chromosome came from the mother, and hence which is from the father, but as Lindert says only the 5% would be known and it wouldn't be known which chromosome that was from. Perhaps some extra deductions could be made using data beyond the simple sequence, such as gene imprinting data (expression of transcripts), DNA methylation, even histone modifications, which might indicate portions of the chromosome that are definitely from the father's Y. Wnt (talk) 23:24, 13 March 2018 (UTC)

U Value for glass

Hi All, just wondering if anyone can tell me, U Value = watts/m2 Degrees Celsius is the calculation to work the U value out but it gives no time frame, is this worked out per hour or day or what ? — Preceding unsigned comment added by 59.167.234.13 (talk) 23:31, 12 March 2018 (UTC)

The Watts unit already includes the characteristic dimension of time, meaning Joules per second. Our writings are available at U value. Graeme Bartlett (talk) 00:03, 13 March 2018 (UTC)

Oops ... yes, that's what the OP was actually asking. ;) ${\frac {watt}{m^{2}C}}={\frac {joule}{m^{2}Cs}}$

I did a web search and the top hit was [4], which I think is a commercial site but gives .22, .25, and .30 as typical values for window units (not just the glass, which as a theoretical continuous surface would be more efficient). They say .30 is a cutoff for federal tax credits, presumably in the U.S. Wnt (talk) 00:07, 13 March 2018 (UTC)

Example, say U-value is 1.1 Wm⁻²K⁻¹. Your sheet of glass is 2 square meters and you want to keep the temperature 20°C warmer on the inside compared to outside. This would then say energy conduced through is 2×20×1.1 = 44 Watts. In an hour this would be 44×3600 158,400 Joules, or in a day 44×3600×24 = 3,801,600 Joules, close to 1 kilowatt hour. Graeme Bartlett (talk) 00:15, 13 March 2018 (UTC)