Wikipedia:Reference desk/Archives/Science/2016 May 5

= May 5 =

Extinction vs. evolution of defense mechanisms
Why is that some groups of animals manage to evolve defensive mechanisms against predators and other threats, while other animals (sometimes from the same taxonomic rank) do not evolve anything and become extinct? Is it about population size and slow rate of predation? Thanks. 93.174.25.12 (talk) 14:24, 5 May 2016 (UTC)


 * It's virtually impossible to say with certainty exactly why similar scenarios can turn out differently in evolutionary history. Lots and lots of factors come into play, and we are not really able to do controlled experiments for these scenarios. But yes, you basically have the right idea. I'll say a little more about the factors and give you some refs that will help you think about this issue: Selective pressure e.g. through predation comes in various strengths. Too low and it won't have much effect, too high and the species is wiped out right away. Allee effects can come into play for very small populations, and in that scenario, random chance can play a big role too. Alternative stable states discusses a little bit about how random fluctuation can lead to different outcomes in ecological models. Apparent competition provides another way of looking at this. If a predator P preys on species A and B, then the dynamics of A and B are actually similar to when A and B compete for a single resource R, because of the predator's prey switching. This gets in to top-down vs. bottom-up control of ecosystems, by species at different places in the food web, see here for a brief description of those effects and  here   for a scholarly review article. Finally, note that in the case where one predator P eats one species A almost exclusively, they will have strong pressure to not eat all of A, because if they did, P could go extinct too. So that's a very broad overview of the forces that influence whether species persist in a sort of Red Queen race or whether one or more go extinct. If you have further questions or would like more specific references let me know and I'm happy to provide more info. SemanticMantis (talk) 14:43, 5 May 2016 (UTC)


 * (ec) Note that extinction isn't just caused by predation, there's also a loss of habitat, food supply, climate change, disease, etc. One way in which predators can wipe out a species is if an invasive species is introduced which is far more capable than the prey, not giving the prey the time they would need to make massive adaptations.  Species limited to islands with no natural predators are particularly vulnerable, like the dodo. On the other hand, if a predator in the same environment slowly evolves more capability to hunt the prey, the prey can evolve an ability to survive that predator at about the same rate. StuRat (talk) 14:45, 5 May 2016 (UTC)
 * Yes, the dodo, and also the Moa. Akld guy (talk) 04:59, 6 May 2016 (UTC)


 * Evolution is the summation of random mutations that enables a life form to compete. If they find that their Ecological niche   is suddenly changing due to say climates changes or/and other predators or animals that are better at competing for the limited food supply moving in, then they may not be able to evolve quickly enough to adapt. This goes for other things as well. Take Microsoft. In the early years it was a predator. Now it a grown to be a slow moving giant dinosaur,  leaving other more adaptive critters to nip at it ankles take away the food it  needs, because they have better evolved and can do so more quickly.--Aspro (talk) 14:56, 5 May 2016 (UTC)


 * Relevent here is Survivorship bias. Much of people's misunderstanding about evolution comes with the notion that, while mutations are random and capricious and arbitrary, only mutations which have "survived" are evident long enough to leave a significant record, so we have the mistaken sense that evolution has a purpose or a goal or makes living things "better".  -- Jayron 32 16:10, 5 May 2016 (UTC)


 * I am actually suspicious that a species can go extinct through lack of predation. The dodo is a classic example, though some now say it has been misrepresented.  If members of a species do not periodically make a run for their lives, will they continue to be able to run?  Etc.  Of course, the dodo never actually became too weak to move ... it just reached a point where it couldn't handle a sudden change for the worse.  A species facing many predators is already at worse, and can't be so greatly surprised.  I even wonder if a prey species tends to evolve a top speed that just barely ensures the predators will keep getting fed with its weaker members, though that would be in a sense a pretty remarkable extreme of altruism, already a controversial concept.  But I have not really seen anything about this. Wnt (talk) 21:02, 5 May 2016 (UTC)
 * Hey do you mean you suspect lack of predation can cause extinction?  Resource competition models show how species can go extinct with no predation. All you need is an uptake rate that's faster than the supply rate. Tilman's R*_rule_(ecology) is relevant here, see also   . But there's no predator even in the picture there. To get at the notion of lack or too little predation, you'd want to have a fairly stable system with say one predator, two consumers, and one resource, then show that removing the predator can cause one of the consumers to go extinct. In concept this could be investigated with microcosms, but I don't know as much about that. For the theory, check out my colleagues Chesson and Kuang (2008)  or maybe some of their other work . I don't know if they have this specific scenario covered, but I suspect they do. Ecological modeling his hard, evolutionary modeling is hard, food web modeling is hard, and very few people have been bold/crazy enough to try to understand all three interacting. There are some simulation models out there that get pretty complicated, but depending on your epistemic stance, those don't really tell us anything about the real world. Then again, depending on your epistemic stance, no model no tells us anything about the real world ;) SemanticMantis (talk) 21:58, 5 May 2016 (UTC)
 * Great answer - it is indeed hard. Even reality seems like a bad model, to be honest.  For example, in the case of the Lake Guri howler monkeys, the long-term effect of losing a predator in the abstract is overwhelmed by the effect of huge extremes in population that occur immediately.  It's like you have to ask what would happen if overgrazing yields a new equilibrium over many years that is not different from the old equilibrium, then would the predator's absence also cause specific changes in the former prey?  It's not even really a coherent question, I guess.  At least, I'm not sure how to frame it properly. Wnt (talk) 22:45, 5 May 2016 (UTC)
 * I wonder if you're getting at the distinction of neutrally stable cycles vs. stable limit cycles. For example in the classic Lotka-Volterra predator prey model, there is nothing to stabilize a preferred amplitude, and both species can come arbitrarily close to zero. This is very different from some other systems/ models, but if you look at the famous Hudson Bay data for lynx and hare pelts (I can't find our copy of this graph), you can see there's no clear lower limit to the fluctuations. It is hard to properly phrase the questions and comments, but if you want to continue the discussion, feel free to drop by my talk page. SemanticMantis (talk) 14:01, 6 May 2016 (UTC)

Percent deviation from additivity
What is the quantitative expression associated to the verbal phrase +/_x % deviation (expansion or contraction) from the addivity of volumes in water ethanol or water salt/sugar solutions?--85.121.32.1 (talk) 15:47, 5 May 2016 (UTC)

Could it be a fraction whose numerator include the difference between the volume of the mixture V and the volumes of the two components V1 and V2 and the denominator equals the sum V1+V2:

$$\%\Delta V_r= \frac{V-(V_1+V_2)}{V_1+V_2} 100$$?--85.121.32.1 (talk) 15:52, 5 May 2016 (UTC)

or $$\%\Delta V_r= \frac{V-(V_1+V_2)} 100$$?

Which one of these two variants of this fraction which can be called relative volume difference are more appropiate?--85.121.32.1 (talk) 15:15, 6 May 2016 (UTC)

Is this question too complicated or intimidating for someone from here to attack it? (just a thought)--85.121.32.1 (talk) 15:32, 6 May 2016 (UTC)
 * I think it's a mainly a language problem. If you post the complete sentence as originally written, it'll be easier for us to work out the meaning.  If the original sentence isn't in English, we'll probably also be able to provide a good translation. Tevildo (talk) 20:42, 6 May 2016 (UTC)
 * Doing some digging, I believe the problem sentence is in Apparent molar property, and I must admit that I don't understand it either. The sentence is:

The nonideality of the solution is reflected by a slight decrease (roughly 2.2%, 1.0326 rather than 1.055 L/kg) in the volume of the combined system upon mixing.
 * My question (which I think mirrors that of the OP) is (a) 2.2% of what?, and (b) where does the 1.055 L/kg come from? 1.0326 L/kg is the specific volume of a 20% w/w mixture of ethanol and water. Tevildo (talk) 07:43, 7 May 2016 (UTC)

Medical Satire
Thinking of putting this suggestion up to WikiProject Requested articles but would like your comments first, as the editors here seem to have both feet on the ground.

Something, I have had simmering on my back burner for years, is that Wikipedia doesn't have an article on Medical Satire yet. There is a lot of it about – one could even say that it is a chronic pandemic. It is my (personal) belief, that it has   a slow incubation period, starting in the early twenty’s (at the same  time when  protection of  one's parental antibodies wains) with signs an symptoms only becoming manifest  in the mid-thirties. Until such time, that medical science can come up with a effective treatment for this malady, is there any Quacks Doctors/nurses/radiographers/hospital porters/morticians/ etc., that can help me to put such an article together?--Aspro (talk) 17:13, 5 May 2016 (UTC)


 * You're talking about this sort of thing, right? Here's   some refs to get you started, lots of refs therein too. I would not have guessed the genre could trace its roots back to the 17th century! SemanticMantis (talk) 18:31, 5 May 2016 (UTC)


 * I don't think Wikipedia needs an article about every combination of literary form and subject matter. Is there something about satire of medicine that makes it more than the sum of its parts? -- BenRG (talk) 19:15, 5 May 2016 (UTC)
 * Well, we already have Political satire and Religious satire (despite "multiple issues"), also Comedy of manners. Alansplodge (talk) 17:51, 6 May 2016 (UTC)
 * Well, those articles sort of illustrate what I'm afraid the medical satire article would be: some boilerplate text along the lines of "satire of X has existed for as long as X; it is a way of avoiding cultural taboos surrounding the direct criticism of X; it can provide valuable insight into the popular perception of X at different points in history", etc., followed by the intersection of "list of works about X" and "list of satirical works". To be fair, there might be value in a separate list of historically important satire about medicine. -- BenRG (talk) 21:23, 7 May 2016 (UTC)

Tiltwinged and thrust vectoring airliners
Thrust vectoring says it's not currently used on commercial aircraft. In practice, what are chances of a commercial airliner with a sort of tiltwings that tilt to a desired angle and thrust vectoring engines for better control of the angle of attack? Costs aside, my understanding is that it would reduce (or eliminate) the possibility of stalling, diving, flat spins and other undesirable aerodynamic effects, so that even in case of pilot error (like Pulkovo Aviation Enterprise Flight 612) the proper airflow could be restored. Brandmeistertalk  20:38, 5 May 2016 (UTC)


 * If such things as tiltwings, tiltrotors, variable-sweep wings, variable-incidence wings and thrust vectoring were considered cost efficient, we would already have operational commercial aircraft with one or more of these features. Since we don't, I have to assume that the cost (in regard to money, weight and added complexity) of adding such features outweighs the benefits of them. WegianWarrior (talk) 21:04, 5 May 2016 (UTC)


 * I know nothing about this, but I had an impression the Bell Boeing V-22 Osprey was not a particularly safe aircraft. Does the benefit of having all those fancy features available for emergencies really outweigh the odds that something going wrong with them will cause an emergency in the first place? Wnt (talk) 22:33, 5 May 2016 (UTC)


 * A predecessor of the proposed Boeing 2707 supersonic transport was planned to have had "swing wings" (variable geometry), but they made the aircraft too heavy and the final design had a delta wing rather like Concorde. Alansplodge (talk) 22:44, 5 May 2016 (UTC)


 * The Concorde did have a movable nose cone, which allowed them to switch from a position with better visibility to one with better aerodynamics. However, the Concorde, despite being used for decades, didn't really prove to be commercially viable in the long term (only 14 were ever put into service). StuRat (talk) 15:00, 6 May 2016 (UTC)


 * All of the concerns listed are minuscule in commercial aviation. Stalling, uncontrolled diving and spins (of any type) are virtually unheard of.  Notable cases such as the Airbus out of Brazil would likely still have a stall/spin because it was commanded.  I'd be more keen on ideas like supercruise that allow fuel efficient supersonic transport.  Also, efficient high-altitude jet design would be a higher priority, imo.  --DHeyward (talk) 09:04, 6 May 2016 (UTC)


 * Agreed. While all of those high-tech additional moving parts might help a fighter plane during a dogfight, just flying more conservatively is enough to make them unnecessary for commercial aircraft. StuRat (talk) 15:00, 6 May 2016 (UTC)


 * According to Accidents and incidents involving the V-22 Osprey; "The V-22 Osprey had 7 hull-loss accidents with a total of 36 fatalities. During testing from 1991 to 2000 there were four crashes resulting in 30 fatalities. Since becoming operational in 2007, the V-22 has had three crashes resulting in six fatalities including one combat-zone crash, and several minor incidents." Alansplodge (talk) 17:43, 6 May 2016 (UTC)
 * Infact all modern commercial airliners have Thrust reversal-"Thrust vectoring" as brake. Beyond that vectoring and Variable-sweep wing make no sense for big planes and with very few, very expensive exeptions, like the Rockwell B-1 Lancer and Tupolev Tu-160, there are no Variable-sweep wings on huge planes because they "only" give you more speed for a very high price and additional risks. Just imagine you would have to make shure a Airbus A380 with defective variable-sweep wing, fixed in its deltawing travel settings, would need to be able to land on an already "almost to short for this giant plane" airstrip. --Kharon (talk) 01:17, 8 May 2016 (UTC)

Could we be in a black hole right now?
Could we (Earth and visible universe) be inside a black hole right now and since the beginning of times? --Llaanngg (talk) 22:35, 5 May 2016 (UTC)


 * See Black-hole_cosmology. Some people find this idea convincing, others don't. I'm not even sure if it's a falsifiable claim or not. SemanticMantis (talk) 22:46, 5 May 2016 (UTC)
 * This exact same question was asked just last month. Vespine (talk) 23:08, 5 May 2016 (UTC)
 * And yet, nobody had linked our most relevant article in that thread. I skipped that round because I don't know much about this topic. But this time I looked around a bit because I felt the last round was unsatisfactory, though there is what looks to be expert commentary from Ben there. Anyway, sometimes it's ok to ask the same question again- sometimes you get different and possibly better references. SemanticMantis (talk) 13:54, 6 May 2016 (UTC)

An antidepressant
I just found out by accident that citalopram, a rather popular antidepressant, is a salt of Hydrobromic Acid. Good Lord, it is a very strong mineral acid. To have it in the GI tract on a daily basis... Isn't it dangerous? --AboutFace 22 (talk) 22:42, 5 May 2016 (UTC)


 * Salt (i.e. table salt) is a salt (chemistry) of hydrochloric acid. The neutralization of an acid into something more neutral is what makes a salt a salt. Wnt (talk) 22:47, 5 May 2016 (UTC)


 * There a comprehensive list of adverse effects here. There are not any GI track specific effects though, only related to SSRI discontinuation syndrome. --Llaanngg (talk) 23:23, 5 May 2016 (UTC)


 * You know your stomach is filled with acid, right? An enormous number of drugs are administered as salts, often hydrochloride salts. --71.110.8.102 (talk) —Preceding undated comment added 05:50, 6 May 2016 (UTC)
 * As above. Your stomach is already at pH 1.5-3.5 (gastric acid, a few mgs more acid isn't going to do much. 213.105.166.119 (talk) 06:46, 6 May 2016 (UTC)