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What Does T. cistoides Have To Do With Darwin’s Finches?

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Because of a prediction, a very strong prediction, I made on another thread, I’ve had reason to look into just what has been happening to Darwin’s finches way off on the Galapagos Islands.

Here is a paper published last year in Science Magazine by the Grants, experts in Darwin’s finches. I looked at their paper, looked at their data, and have come to the conclusion that what I predicted as the ultimate explanation to changed beak sizes is the more reasonable interpretation of the data they present.

But before we even get to the data, here’s a remark from a National Geographic website review of the article that supports my basic position:

“ Researchers from New Jersey’s Princeton University have observed a species of finch in Ecuador’s Galápagos Islands that evolved to have a smaller beak within a mere two decades.
Surprisingly, most of the shift happened within just one generation, the scientists say.”

The shift happened in ONE year? What kind of population genetics are at play here?

Well, to the data:

The most important information that we get from the article (only 3 pages in pdf) are contained in Table 1 and Figure 2.

The Grants’ paper is concerned with how Geospiza fortis and Geospiza magnarostris compete. Their conclusion is that during the drought years of 2003-2004, when the population numbers of both species fell drastically, that the “competition” from G. magnarostris, due to the numbers of both species being almost the same for the first time since G. magnarostris came over from the mainland, caused “character displacement” (beak size change) of G. fortis to a smaller size.

Table 1 gives the number of observed feedings of the three main seed types (small, medium, large) by each of the species. Figure 2 gives the beak size mean of G. fortis over the last 33 years, beginning in 1973-74.

The Grant’s give four ‘lines of support’ for their conclusion. Their fourth ‘line of support’, I believe, becomes the very reason for re-interpreting their results. The fourth ‘line of support’ is that in the drought year 1977, when G. magnarostris were few in numbers, and hence, not able to compete with G. fortis, the beak size of G. fortis actually increased so as to be able to take advantage of the Tribulus cistoides seeds (the large ones), whereas in 2004, with a similar drought taking place, but, however, with G. magnarostris now able to compete with G. fortis, the beak size of G. fortis decreased.

Let’s first notice all of Figure 2. For most of the 33 years that it records beak size, the beak size hardly fluctuates from its mean; there are only two noticeable/significant exemptions: the two drought periods, when, in BOTH instances, beak size changed almost ‘instantaneously’. The title of the National Geographic review had “instant” in its title.

Now to my prediction: my prediction is that changes in the morphology of species is driven mostly, if not completely, by environmental ‘triggers’. Table 1 now becomes important. Notice the difference between the observed feedings of G. fortis between 1977 and 2004. While both were small, the number of feedings on T. cistoides for G. fortis dropped from one sixth for 1977-1989, to one twelfth for 2004—half as much! But that’s not all of the story. In the paper, the Grants indicate that when examing these lowered ‘feedings’, whereas in normal years an average ‘feeding’ on T. cistoides was 9 to 23 mericarps, in 2004 it was never on more than 2 mericarps. That’s a factor of somewhere between 5 and 12. Taken altogether, then, this means that the amount of T. cistoides consumed by G. fortis fell in 2004 to somewhere between one tenth, and one twenty-fourth, of its normal consumption.

Let’s also notice that while both G. fortis and G. magnarostris were decimated, G. magnarostris did not change its beak size to a smaller one. If we look at ‘feeding’ observations for G. magnarostris we see that while they ate a larger proportion of the medium sized seeds than normal, nonetheless, their main intake continued to be T. cistoides.

The more reasonable interpretation of the Grants data is this: there is some protein(s) found in T. cistoides that cause beak size (and other (6) correlated characteristics, see Table 2) to increase, and that in the absence of these protein(s) beak size will diminish. The most likely method of this change is, I believe, through a changed developmental pattern in the next generation. (One possibility is that RNA is involved here, and that somehow the presence of protein(s) that come(s) from the ‘large’ seeds is able to transmit the fact of its presence, or absence, to the subsequent generation).

This thesis, though controversial perhaps, renders what we see—over a 33 year history—sensible, because: (1) It explains why G. magnarostris, despite being decimated by the drought, still does not change—since it is still principally ‘feeding’ on T. cistoides; (2) It explains why G. fortis changes beak size in ONE generation (“Instant” evolution); and (3) most importantly, it explains why in 1977, at a time when G. magnarostirs was very small in numbers, G. fortis INCREASED its beak size in ONE generation; that is, since there were no G. magnarostris to compete with, the G. fortis had all the T. cistoides to themselves. In the next generation beak size “popped-up” in size to the same degree that it decreased in size during the 2004 drought when their consumption of T. cistoides dropped drastically.

As a follow-up to this study, here is what the Grant’s propose: “Our findings should prove useful in designing realistic experiments, by identifying ecological context (high densities at the start of an environmental stress) and by estimating the magnitude of natural selection.

Here is what I consider to be another important point in all of this. From an ID perspective, this kind of an experiment is a complete waste of time. What would be valuable, OTOH, is an experiment wherein native Galapagos seeds are fed to controlled populations of G. magnarostris and G. fortis while observing changes to beak size (and other traits that are correlated). You see, ID really is “science”!

Finally, let’s remember that Kettlewell’s experiment and the Galapagos Finches are the Modern Synthesis’ great claims to fame. Well, I think they got it completely wrong. What do you think?

70 Replies to “What Does T. cistoides Have To Do With Darwin’s Finches?

  1. 1
    Gerry Rzeppa says:

    A significantly larger than normal beak – not present in the previous several generations – can be observed at Google Images with a search for “Jimmy Durante”. Since no direct descendents with this particular characteristic have been found, it appears that Durantus Jimminus – a chance mutation of the pedestrian Durantus species – was rejected by natural selection and failed to reproduce for reasons as yet undiscovered. Further study is required, but it is clear that beak size is an important and defining characteristic of species.

  2. 2
    PaV says:

    LOL Gerry!

  3. 3
    SCheesman says:

    So all the vaunted changes in beak sizes on the Galapagos Islands could be due to epigenetic factors, not natural selection at all?

    Down with Darwin! Bring back Lamarck!

    The mind reels.

    This is such a simple case of cause-effect, and I’d say publishable, at least as a letter. Well done, PaV!

  4. 4
    SCheesman says:

    PaV – the link to the paper doesn’t seem to work.

  5. 5
    SCheesman says:

    Ditto for the National Geographic article.

  6. 6
    Unlettered and Ordinary says:

    Greetings!

    So your hypothesis is that the food releases some kind of growth element or trigger.

    Kinda like McDonalds in Japan. Little people becoming giants. Growth hormones in food that affect growth and development. Something along those lines. Sound experimental, sounds like, ah ah hmmm… oh science.

    I really would be interested in the results on such an experiment. Definitely worth an experiment or two or three or more.

  7. 7
    PaV says:

    SCheesman:

    The links are fixed now. Thanks for pointing that out. I put in the formatting from Windows, and, believe it or not, the quotation marks from Windows don’t work.

  8. 8
    PaV says:

    Unletterd and Ordinary:
    Kinda like McDonalds in Japan.

    Exactly. Families coming over from Europe during the first half of last century experienced something like this too. Whether it’s a protein that gets involved in the soma of an organism, and thus finds itself to the ova, or whether there is some way in which the protein is somehow translated into codable RNA that finds its way to the ova, something along those line is what I’m thinking of. There was an article about a year or so ago talking about non-Mendelian inheritance. ( Here’s one link. ) I’m wondering if it’s a more common mechanism that previously known.

  9. 9
    DLH says:

    Since I can’t read the Grant pdf, I presume this is the article cited:
    Evolution of Character Displacement
    in Darwin’s Finches; Peter R. Grant and B. Rosemary Grant Science 14 July 2006: Vol. 313. no. 5784, pp. 224 – 226


    “Instant” Evolution Seen
    in Darwin’s Finches, Study Says;
    Mason Inman for National Geographic News July 14, 2006 (printer formatted)

    Google Scholar lists the following citations to Grants’ 2006 Science article

  10. 10
    Michaels7 says:

    Hmmm,

    PaV, maybe you have all the research data on file that is required thru other massive amounts of research.

    What immediately came to mind was drug abuse symptoms. A female, impregnated who does not stop addiction to alcohol, crack, cocaine, even sugary diets. Is there any reason this is not the same type of observation but with a deleterious effect?

    Environment stimuli do matter, whether input thru chemical man made substances or natures protein growth hormones.

    There should be a lapse time and preceeding time frame for food or drugs to work thru systems.

    The “instant” evolution however works with current information still in the genome, like the blind fish, where 40% receive functional eyes from one hybridization.

    So, we see 1) informational overlap and “regain” by hybridization of species and 2) environment input factors that have instant change.

    None of this I see as related to macro-evolution or forces strong enough to create new information. It can only regain lost information or extend what is there in positive or negative forms.

  11. 11
    DLH says:

    PaV
    Strongly encourage you to pursue and publish your observation.

    Recommend posting a graph these parameters as described.

    See the following for the impact of nutrition on growth:
    Early Nutrition Causes Persistent Effects on Pheasant Morphology, Ohlsson & Smith, Physiological & Biochemical Zoology 74(2):212-218, 2001
    “Differences in growth conditions during early ontogeny have been suggested to cause permanent affects on the morphology and quality of birds. . . . An experimental increase in the first 3 wk of life accelerate growth . . .”

    Effects of nestling diet on growth and adult size of zebra finches (poephila guttata) Peter T. Boag, The Auk, Vol. 104, April 1987, No. 2 p 155-166.
    “. . . a low-quality diet reduced growth rates of nine external morphological characters, while a high-quality diet increased gowth rates. . . .”

    See also: Citations to Boag 1987

    Nestling diet, secondary sexual traits and fitness in the zebra finch, TR Birkhead. Proc. Biological Sciences, Vol. 266, No. 1417, Feb 22, 1999 pp 385-390

    Also see the studies showing dramatic differences in size based on nutrition for human populations with similar genetic makeup. e.g. the studies of height of Japanese in Japan vs Japanese Americans in the last half of the 20th century.

    Your observation on the difference in see diet may reveal a specific nutrient strongly effecting growth separate from general nutrition. Both factors are worth exploring, especially seeing the strong difference in the table – and the implications for origin theories.

  12. 12
    shaner74 says:

    Great work PaV! I wasn’t aware the change occurred so rapidly. I think your idea is dead on.

  13. 13
    DLH says:

    PaV
    Here is an example of another “instant” dramatic change in ONE generation – of humans.

    Increase in length of leg relative to trunk in Japanese children and adults from 1957 to 1977: comparison with British and with Japanese Americans.
    Tanner JM, Hayashi T, Preece MA, Cameron N. Ann Hum Biol. 1982 Sep-Oct;9(5):411-23.

    “Adult height increased by 4.3 cm in boys and 2.7 cm in girls between 1957 and 1977, the increment being less in the second decade than in the first.”

    Secular changes in relative leg length in post-war Japan.
    Ali MA, Uetake T, Ohtsuki F.
    Am J Hum Biol. 2000 May;12(3):405-416.

    “A significant trend towards greater relative leg length (long-leggedness) among Japanese children and youth has occurred during the period of about four decades covered by this study. After showing a strikingly consistent trend at all age levels between 6 and 17 years and a dramatic trend during the birth-year age period 1943-1963, the relative growth in leg length has been rapidly slowing or has stopped in both sexes.”

    I think it will be important to compare changes against the typical time per generation for the species.

  14. 14
    AussieID says:

    What the Grants have shown, in my opinion anyway, is that true genetic novelties have NOT arisen.

    Their meticulous work has continued to display that with rainfall patterns, and the corollary of hard seed types remaining, that beak length gets longer or shorter. Climatic change brings beak lengthening, and when it oscillates back to the standard, beak shortening occurs.

    The situation is observable (drought v rains) but the trigger to cause the involuntary beak change has not. The idea of this food source as being the reason behind the beak lengthening is very interesting PaV, and I hope it goes somewhere.

    I’ve studied, though not in depth, the Grants work and have always been slightly confused. On Daphne Major, the studied group pre-drought (1976) was 751 birds. After the ’77 drought the studied survivors numbered 90. The ’76 graph show the standard curve, the ’78 graph has a discernible peak between 10 and 10.5 mm for beak depth. This group of birds is really the focus of the whole study. If only 10 of those birds had not made it, I wonder if the study would have made such news. The curve would, in all respects, have been a less populated version of what was before and, except for this one particular spike, it is the classic curve.

    I’ve always considered there has been a lot of spin in this icon, and a less revered look at it could show many inconsistencies rather than evolutionised elegies. Rationalism V Empiricism?

    A lot has been written and eulogised over 2-3mm!

  15. 15
    Atom says:

    Good discussion PaV. Reminds me of Dr. Lee Spetner’s book, where he comes to the same conclusion and uses it as a starting point for his “Non-Random Evolutionary Hypothesis.” He gives examples from different species, including how the presence (or absence) of predators can also trigger “built-in” development responses.

    From “Not By Chance” page 200:

    Crabs prey on snails with thin shells, but they cannot eat snails that have thick shells. Snails can somehow tell if crabs are around. In the presence of crabs they grow a thick shell [Stearsn 1989]. This adaptation clearly helps protect the snails from the crabs.

    Snails are themselves predators. They prey on barnacles. When the barnacle senses snails, it protects itself by growing into a bent-over shape that keeps the snails from eating it. When there are no snails around, the barnacle develops into its normal straight form. [Stearns 1989, Lively 1986].

    I am suggesting here that organisms have a built-in capacity of adapting to their environment. I am suggesting that to the extent that evolution occurs, it occurs at the level of the organism. This suggestion differs sharply from the thesis of the NDT [Neo-Darwinian Theory], which holds that evolution occurs only at the level of the population. Organisms contain within themselves the information that enables them to develop a phenotype adaptive to a variety of environments. The adaption can occur by a change in the genome through a genetic change in the environment, or it can occur without any genetic change.

  16. 16
    PaV says:

    Atom (15):

    I’ve read Spetner’s book, and thought it was one of the best I had read on genetics and such. Thanks for pointing out the similarities. I don’t think my ideas here are a result of his, but it certainly is time to pick up his book again and reread. Thanks.

  17. 17
    PaV says:

    DLH:

    I tried to post earlier, and apparently something happened to it.

    You seem to be right on top of this side of the evolution debate. Thanks for the references—you’re going to keep me busy for a while.

    As to a paper, I think Dembski’s approach is good: put it out online, and then with criticisms in hand, publish. Quite honestly, if you want to run with it, I’m happy either to work something out with you or let you run with it–whatever works out best.

    shaner74:

    I was quite surprised myself by the suddenness.

  18. 18
    PaV says:

    DLH:

    Checking out your links, it looks like all the literature citations I need have already been accounted for! 🙂

    Those references sure make me feel stronger about the conclusions I’ve reached. The above offer still stands. I’m waiting to hear from Bob O’H, for example. Got to run.

  19. 19
    Bob O'H says:

    PaV – I’m on it, but I have to do some work first…

    Bob

  20. 20
    Bob O'H says:

    OK, now I’ve looked at the paper, and I think there’s a slight problem.

    Now to my prediction: my prediction is that changes in the morphology of species is driven mostly, if not completely, by environmental ‘triggers’.

    Now, this could be read as suggesting a change in adult birds, but beak length is stable in size in adults. So…

    The most likely method of this change is, I believe, through a changed developmental pattern in the next generation.

    this would be a better interpretation – in essence, a form of Lamarckian inheritance. It would then mean that juvenile birds would have smaller beaks, but adults would have beaks of the same size (well, assuming no variation in survival!).

    Here’s the problem. From the Grant & Grant paper:

    Little rain fell in 2003 (16 mm) and 2004 (25 mm), there was no breeding in either year, numbers of both species declined drastically, and from 2004 to 2005 G. fortis experienced strong directional selection against individuals with large beaks (26).

    (bolding mine, italics in the original)

    There was no recruitment into the population (except possibly by immigration), so there was no next generation to have smaller beaks.

    “The great tragedy of science – the slaying of a beautiful hypothesis by an ugly fact” – T.H. Huxley

    Bob

  21. 21
    hrun0815 says:

    PaV, I think your hypothesis would be very easy to verify with available data.

    According to your theory, there should be a drastic discontinuity of beak size either in the individuals that fed less on the T. cistoides seeds or in their offspring. That is, either the beaks of the individuals should shrink, or, the beak sizes of the offspring should be significantly smaller than the average beak size of the parents.

    In contrast, according to the Grant’s theory, the beak size of the individuals should not change and the beak size of the offspring would be directly correlated to the average beak size of both parents. What actually changes the beak size of the population is that the individuals with smaller beaks produce more offspring than the individuals with larger beaks.

    Why don’t you go over the published data and see which theory the data supports?

  22. 22
    DLH says:

    Bob
    Good observation.

    Curious the phrase
    “strong directional selection against individuals with large beaks”

    Extrapolating PaV’s concept, could the change or differential survival be due to different nutrition based on the different type’s of seeds eaten?

  23. 23
    PaV says:

    Bob O’H:

    It turns out that your ‘fact’ isn’t ‘ugly’ at all—in fact, it’s quite pretty.

    Here’s what I mean. When I read “breeding”, I think of active, human agents being involved, and understood things this way. I would have expected “there was no mating in either year.”

    That said, this “ugly fact”, i.e., that the populations didn’t breed (which also is suggestive of an ‘environmental trigger’), actually clears up two things that concerned me: (1) that the average beak size went up slightly in both 2003 and 2004 before decreasing. The fact that no young were produced each of those years explains this fact. So, 2005 was, in fact, the first year that young were produced, and we see the ‘instaneous’ decrease in beak size that year. (2) There is sizable variance in beak size for the year 2005; but, of course, if you have adults with average size (large) beak sizes (the drought is over), and young with small beak sizes, then you would expect a lowered mean, and a large variance—which is exactly what we see.

    No mention is made of there being no ‘breeding’ during the 1977 drought, and for that year we see an immediate jump in beak size. The variance seems small, which might mean that when beak sizes were measured many of the ‘adults’ had died, leaving mainly the ‘young’ that had the larger beak size.

    As to the ‘environmental triggers’ and such, yes, I’m thinking of something along the lines of Lamarck…….but ALSO along the lines of Darwin’s idea of panspermia (??? was that what he called it?) wherein various organs and parts of the body send a kind of ‘seed’ to the reproductive organs. This blend of the two might account for why two brilliant minds came up with separate theories with neither one fully capturing the phenomena they so carefully observed. Of course, time will tell in all of this.

  24. 24
    ari-freedom says:

    pangenesis

  25. 25
    ari-freedom says:

    from Atom’s Spetner quote
    “The adaptation … can occur without any genetic change.”

    and on p 194-197 he explains how the population can change in phenotype with no genetic variation or selection. Cultural channels could change the entire population and it would look as if something was inherited.

  26. 26
    Bob O'H says:

    Extrapolating PaV’s concept, could the change or differential survival be due to different nutrition based on the different type’s of seeds eaten?

    That’s more or less what Grant and Grant say – G. fortis was forced to shift to a less optimal source of nutrition. I guess if you allow different nutrition to include less nutrition, you’re saying the same thing.

    (1) that the average beak size went up slightly in both 2003 and 2004 before decreasing. The fact that no young were produced each of those years explains this fact.

    How so?

    (2) There is sizable variance in beak size for the year 2005;

    Where do you get that from? I can’t see it in the paper.

    Bob

  27. 27
    Mapou says:

    ari-freedom: and on p 194-197 he explains how the population can change in phenotype with no genetic variation or selection.

    Interesting. So what we have here is phenotypic adaptation without natural selection. Isn’t that contrary to ND theory? And isn’t that supporting the ID hypothesis that a designer anticipated future environmental changes and pre-loaded the genome with enough anticipatory information so as to adapt? This watchmaker was anything but blind. He could see into the future.

  28. 28
    PaV says:

    Bob O’H:

    How so?


    Look at what happened in 1977. It was a drought year. Beak sizes went up; feeding on T. cistoides causes beak sizes to increase. It might even have that effect on adults from year to year. But part of the increase could just simply be due to sampling differences from year to year. The real point is that the non-breeding (non-mating) explains why there wasn’t a “decrease” in the beak size those years.

    Where do you get that from? I can’t see it in the paper.

    The size of the confidence interval and the standard deviation are directly related. Variance is simply the standard deviation squared. You’ll notice an unusually large confidence interval for 2005.

  29. 29
    hrun0815 says:

    The size of the confidence interval and the standard deviation are directly related. Variance is simply the standard deviation squared. You’ll notice an unusually large confidence interval for 2005.

    The large size of the confidence interval is not necessarily due to a large variance. Typically, the confidence interval is not the standard deviation but the standard error of the mean. It is therefor dependent on sample size (the larger the sample size, the smaller the standard error of the mean). Thus, the larger confidence interval is not necessarily due to a larger variance but more likely due to the fact that the sample size (the number of each species) declined drastically in those years.

  30. 30
    PaV says:

    Mapou:

    And isn’t that supporting the ID hypothesis that a designer anticipated future environmental changes and pre-loaded the genome with enough anticipatory information so as to adapt?

    If we want to play with things for a second, in a plant study on Arabadopsis a few years ago, the experimenters found that there were a kind of set of ‘templates’, RNA templates, found in the germ cells, and that these ‘templates’ came from more than one generation back, with the ability to sort of “substitute” different “versions” of particular genes.

    As I say, if we play with all of this, we could then suggest that what happens in nature—flora and fuana, plants and animal—is that some kind of patterning takes place over a number of generations. Along the lines of voice-controlled software, where you have to pronounce certain words the program gives you so that the program can learn your inflection patterns, maybe in a particular environment, with a particular food source, a pattern/template is established and stored (!!), like RAM memory, wherein the regulatory mechanism for the genome is geared to the environmental conditions that prevail in a particular year(s). IOW, in drought years, use Program D; in wet years use Program W. Based on the dietary inputs for a given year, ‘templates’ are brought out from the organism’s genetic ‘memory’ (perhaps using RNA instead of DNA, and built up over decades of environmental change), and “run”, as we would say.

    The idea really does make a whole lot of sense. (And makes Lamarck a bit more of a hero!)

  31. 31
    PaV says:

    Bob O’H:

    That’s more or less what Grant and Grant say – G. fortis was forced to shift to a less optimal source of nutrition. I guess if you allow different nutrition to include less nutrition, you’re saying the same thing.

    That doesn’t do justice to the data. Yes, there is a competitive population component to all of this—as seen in comparing 1977 t0 2005. But the morphological change is entirely due to diet, and has almost nothing to do with a competitive population being present. The ‘trigger’ is dietal. The competitive population—and the lack of rain!!— simply has a role in what the diet consists of in a given year.

  32. 32
    van says:

    I think it’s pretty clear that the consumption of a different, more-difficult-to-eat seed is causing the release of a hormone in the mother, which not only may alter her beak size/shape, but also alter the beak of her offspring. Lamarck was right.

  33. 33
    Bob O'H says:

    Bob O’H:

    How so?

    Look at what happened in 1977. It was a drought year. Beak sizes went up; feeding on T. cistoides causes beak sizes to increase. It might even have that effect on adults from year to year. But part of the increase could just simply be due to sampling differences from year to year. The real point is that the non-breeding (non-mating) explains why there wasn’t a “decrease” in the beak size those years.

    What are you saying?
    (1 )that beak size increases in adults?
    (2) that the change was just sampling variation? It would seem to be a coincidence that such a huge change would coincide with the drought.

    And how does non-breeding explain why there wasn’t a decrease? Does bill size change in adults?

    I’m sorry,

    Where do you get that from? I can’t see it in the paper.

    The size of the confidence interval and the standard deviation are directly related. Variance is simply the standard deviation squared. You’ll notice an unusually large confidence interval for 2005.

    Fig. 2 shows the 95% confidence interval for the mean. This also depends on the sample size. If you read the text, you’ll see that that is the year with the lowest sample size. On its own you can’t use it to say anything about the variance in the trait.

    Bob

  34. 34
    PaV says:

    Bob O’H: (31)

    What are you saying?
    (1 )that beak size increases in adults?
    (2) that the change was just sampling variation? It would seem to be a coincidence that such a huge change would coincide with the drought.

    And how does non-breeding explain why there wasn’t a decrease? Does bill size change in adults?

    I’m referring to Figure 2. The drought years were 2003 and 2004. No breeding occurred those years, meaning, no young were hatched. So, in 2003, we’re only dealing with adults. In 2004 we’re only dealing with adults. In 2005, we’re dealing with both adults and young finches.

    As to the increase in the beak size of adults, here are two observations: (1) is it entirely impossible for adult features to change under the influence of certain proteins/chemicals ? We have the recent case of steroids and baseball, for example. (2) We’re talking about changes that fall within the confidence interval of the previous year; IOW, it’s a minor change.

    That’s why I said that it could be due simply to sampling differences from one year to the next. But the reference was to the years 2003-2004. The “huge change” you refer to happened in 2005.

    Non-breeding explains why there wasn’t a “decrease” in either drought year. It’s simply because there were no ‘young’ being hatched. So, in 2003 and in 2004 there were only adults to sample. All the change the Grants report happened in one year: 2005.

    To me, everything is very consistent with the hypothesis I propose. OTOH, the Grants have to explain how such a large change occurred in just “one” generation.

  35. 35
    Bob O'H says:

    I’m referring to Figure 2. The drought years were 2003 and 2004. No breeding occurred those years, meaning, no young were hatched. So, in 2003, we’re only dealing with adults. In 2004 we’re only dealing with adults. In 2005, we’re dealing with both adults and young finches.

    If there was no breeding in 2004, then there were no new adults in 2005 (unless through immigration) – young finches in one year become adults in the next year. This is how the legend to Fig. 1 starts:
    “Mean beak size PC1 bill of adult G. fortis (sexes combined) in the years 1973 to 2005.” Grant and Grant were only studying adult birds, so the 2005 recruits were not measured.

    (1) is it entirely impossible for adult features to change under the influence of certain proteins/chemicals ? We have the recent case of steroids and baseball, for example.

    What position does the Darwin’s finch usually play? The ball? 🙂

    More seriously, we’re talking about skeletal morphology here, not soft tissue. We’re also talking about a part of the body that isn’t surrounded by soft tissue, so it’s difficult to see how changes in the size and shape could be rendered.

    It might be that it’s possible that beak size can change in adult finches, but you would need to dig through the literature yourself to find the evidence. It’s a part of doing science, we’ve all had to do it.

    Non-breeding explains why there wasn’t a “decrease” in either drought year. It’s simply because there were no ‘young’ being hatched.

    Ah, I see. You haven’t read the paper properly. Only adults were measured.

    OTOH, the Grants have to explain how such a large change occurred in just “one” generation.

    They do that. That’s what all the talk is about selection differentials is about – comparing the beak sizes of survivors and individuals that died.

    Bob

  36. 36
    PaV says:

    Bob,

    you say that I’m not reading the paper correctly. You say that no breeding, hence no young, were born in 2004, and that the young from one year become the adults in the next year, and you say that adult morphology, at least hard tissue like beaks doesn’t change. So, then, please explain why the beak size changed in the year 2005.

  37. 37
    hrun0815 says:

    Bob,

    you say that I’m not reading the paper correctly. You say that no breeding, hence no young, were born in 2004, and that the young from one year become the adults in the next year, and you say that adult morphology, at least hard tissue like beaks doesn’t change. So, then, please explain why the beak size changed in the year 2005.

    Because mortality of G. fortis in that year was strongly correlated to beak size.

  38. 38
    Bob O'H says:

    Because birds with big beaks died. That’s what the stuff about selection differentials is saying.

    Bob

  39. 39
    van says:

    Bob…even if the drought caused the death of birds with the ill-fitted beaks, that still does not provide evidence for the origin of the fit. The origin of the fit is ultimately what’s in question here: was it merely randomness or accidental — or was it somehow directed from within the organism as a response to the environment.

    Creationists/IDists don’t generally have a problem with the idea that selection can weed out the less fit — we just don’t believe that this is the explanation for the arrival of the fit. In this case, the arrival of the fit surely came about as a developmental phenomenon whereby the mother finch (assuming she lived, of course) somehow “sensed” this new diet (new diets can certainly be a stressor if the right morphology is not in place to consume it properly)…and this probably generated specific hormones which acted on the genetic program of her developing embryos.

    This guy says it a bit better than I have:

    http://www.biology.duke.edu/ni.....henism.htm

    “It appears that in the control of polyphenic development, hormones act as stimuli that induce discrete switches in developmental pathways. There is independent regulation of the pattern of hormone secretion, of tissue receptivity to the hormone, and of the developmental response of each tissue to the hormone. Because hormone secretion is regulated by the central nervous system, this mechanism allows development to become responsive to environmental variables. Variation in tissue sensitivity to the hormones allows the developmental switch to produce alternative phenotypes in response to specific environmental signals. This is interesting from an evolutionary perspective because genetic variation in the signal and the response mechanisms provide the basis for the evolution of adaptive developmental responses to environmental contingencies.”

    All this is quite testable on finches — so where are the experiments?

  40. 40
    hrun0815 says:

    Creationists/IDists don’t generally have a problem with the idea that selection can weed out the less fit — we just don’t believe that this is the explanation for the arrival of the fit. In this case, the arrival of the fit surely came about as a developmental phenomenon whereby the mother finch (assuming she lived, of course) somehow “sensed” this new diet (new diets can certainly be a stressor if the right morphology is not in place to consume it properly)…and this probably generated specific hormones which acted on the genetic program of her developing embryos.

    Van, remember that there was no breeding in the drought year. So in order for you theory to be true, the mother finch would have had to sense the drought year before it occurred and thus impart the changed beak to their offspring so they could survive the upcoming drought of 2005.

    Is that what you are suggesting?

  41. 41
    PaV says:

    Finches reach adult size in six months. The breeding season is early in the Galapagos. That means that at the end of a given calendar year, it’s possible to be measuring those finches that were hatched earlier that year. So, do the measurements of beak size in the year 2005 represent the “new” generation mixed with the parental generation, or is it simply the remanants of 2003-2004. That is the question before us.

    I looked at the supplemental data on methods. They measured the number of adults in the first three months of each year. Presumably, this is also when they made the measurements. They also say that the “2005 generation measured in 2006 was significantly smaller than that in the 2004 sample of the parental generation before selection.”

    Taken together, this means that we’re dealing with the effects of attrition, and not an environmental trigger. I grant this much.

    But I nonetheless think that this data has been misinterpreted.

    The better conclusion would be that the smallest G. fortis had a selective advantage in the second year of the drought rather than the larger G. fortis being disadvantaged by the presence of G. magnarostris.

    Here’s why:
    (1) In the drought year 1977, they state that the mortality that year was heaviest amongst the smaller G. fortis. This makes a lot of sense. We’re told that only the large-beaked G. fortis can crack open the T. cistoides seed. That means that in a drought year, when the flora is limited, the large-beaked G. fortis can eat the small, the medium and the large seeds, whereas the smaller G. fortis can feed only on the small and the medium.

    (2) In line with the expectation that in a drought year the large G. fortis would do better than the smaller one, we see a rise in mean beak size in 2004 over that of 2003; that is, after the first year of the drought.

    (3) What becomes critical in the second year of the drought is NOT the competition between the large-beaked G. fortis and the G. magnarostris, but the fact that the smallest-beaked G. fortis had an additional food source which the large G. fortis did not have. Why do I say this? Two reasons: (a) T. cistoides, we’re told, does not reproduce in a drought year. After two consecutive drought years, very little T. cistoides seed would have been available for feeding in 2004. This is what indeed happened since the G. magnarostris, who feed almost exclusively on the T. cistoides, were almost completely wiped out. But for the large G. fortis this would only represent a loss of an advantage it would normally have over the small G. fortis, as it had had the previous year (again, the mean beak size went up in 2004!); (b) we’re told that in the midst of this great competition for food between the large and the small G. fortis “[t]he only escape was [the one] avialable to the smallest, most G. fulginosa-like, members of the G. fortis population, which are known to feed like G. fulginosa on small seeds with little individual energy reward.”

    So, with two consecutive drought years resulting in very little T. cistoides, and its availability diminished due to the presence of the G. magnarostris, the large-beak G. fortis have to now compete with all of their fellow G. fortis for the available small and medium seed. In this environment, the “smallest” G. fortis are the ones who have an advantage because of the avaiability of small seeds. So, the “smallest”-beaked G. fortis will survive better than any others. This would then be the reason that the mean beak size changed the most it had ever been seen to do in the 33 years of measurement.

  42. 42
    hrun0815 says:

    The better conclusion would be that the smallest G. fortis had a selective advantage in the second year of the drought rather than the larger G. fortis being disadvantaged by the presence of G. magnarostris.

    I don’t see how you can argue that large G. fortis where not being disadvantaged by the presence of G. magnarostris, a direct competitor for their main food source already in very low supply due to a drought in the previous year.

    In addition, the authors agree that these results do not prove their conclusions, but they do give strong evidence to support them:

    Replicated experiments with suitable organisms are needed to demonstrate definitively the causal role of competition, not only as an ingredient of natural selection of resource-exploiting traits (12) but as a factor in their evolution (33). Our findings should prove useful in designing realistic experiments, by identifying ecological context (high densities at the start of an environmental stress) and by estimating the magnitude of natural selection.

    So maybe now, after this discussion, you would agree that even from an ID point of view, the suggested experiments are actually not a waste of time and that OTOH looking for proteins in the seeds that affect beak size might not be warranted.

  43. 43
    DLH says:

    PaV
    Sounds plausible.
    How would you propose testing these competing parameters?

  44. 44
    PaV says:

    DLH:

    In the wild, you’d have to wait for a situation in which you had two drought years in a row at a time when the G. magnarostris is not numerous. But I wonder if that will take another 33 years.

  45. 45
    DLH says:

    How about in the lab?

  46. 46
    PaV says:

    hrun0815:
    I don’t see how you can argue that large G. fortis where not being disadvantaged by the presence of G. magnarostris, a direct competitor for their main food source already in very low supply due to a drought in the previous year.

    On what basis are you saying that the T. cistoides were the main food source for G. fortis?

    As to environmental triggers, why did the finches not breed in drought years? Just a coincidence?

    And, as far as ID and microevolution is concerned, most IDers readily accept the results of microevolution. They would disagree, of course, that anything as simple as microveolution could be projected out and serve as an explanation for macroevolution.

    DLH: I think it would be hard to capture in the lab what happened in the wild here. I think whatever you did in the lab might not ever survive charges that the results depend on an artifical environment that was created in the lab.

  47. 47
    Bob O'H says:

    What becomes critical in the second year of the drought is NOT the competition between the large-beaked G. fortis and the G. magnarostris, but the fact that the smallest-beaked G. fortis had an additional food source which the large G. fortis did not have.

    Huh? Where’s your evidence that large-beaked G. fortis can’t feed on small seeds?

    G. fortis usually feeds on small seeds (and Opuntia in our winter, see ref. 15 in the paper). During the drought in the 1970s, they switched to larger seeds. They couldn’t do this in 2005, because G. magnarostris was excluding them.

    So, with two consecutive drought years resulting in very little T. cistoides, and its availability diminished due to the presence of the G. magnarostris, the large-beak G. fortis have to now compete with all of their fellow G. fortis for the available small and medium seed. In this environment, the “smallest” G. fortis are the ones who have an advantage because of the avaiability of small seeds. So, the “smallest”-beaked G. fortis will survive better than any others. This would then be the reason that the mean beak size changed the most it had ever been seen to do in the 33 years of measurement.

    And that’s more or less what Grant and Grant conclude.

    Bob

  48. 48
    larrynormanfan says:

    Van [39], are you suggesting that Nijhout’s work is creationist or IDist? Doesn’t look that way to me.

  49. 49
    larrynormanfan says:

    PaV,

    Taken together, this means that we’re dealing with the effects of attrition, and not an environmental trigger. I grant this much.

    Only that much? Why, that’s the whole shootin’ match. Time to cry “uncle.”

  50. 50
    hrun0815 says:

    PaV:

    On what basis are you saying that the T. cistoides were the main food source for G. fortis?

    I don’t think that T. cistoides is the main food source for G. fortis in general, but that it is the main food source for LARGE G. fortis in times of DROUGHT. From the paper:

    G. magnirostris is a potential competitor as a result of diet overlap with G. fortis (Table 1), especially in the dry season when food supply is limiting. Large-beaked members of the G. fortis population are capable of this maneuver—indeed, survival in the 1977 drought to a large extent depended on it (13, 16)—but on average they take three times longer than G. magnirostris to gain a seed reward (13, 24). The smallest G. fortis never attempt to crack them (18, 24).

    PaV:

    As to environmental triggers, why did the finches not breed in drought years? Just a coincidence?

    Of course not. Who would suggest something like that? The environmental trigger was most likely that the population of finches was rapidly starving to death. Starvation induced delay or inhibition of ovulation has been shown to occur animals as varied as cockroaches and mice.
    PaV:

    And, as far as ID and microevolution is concerned, most IDers readily accept the results of microevolution. They would disagree, of course, that anything as simple as microveolution could be projected out and serve as an explanation for macroevolution.

    At no time in this thread did anybody here bring up microevolution or use it as an explanation of macroevolution. As far as I’m concerned we were discussing a scientific paper on finches that you suggested falsely interprets the data. You suggested an alternative interpretation that turned out to be false.

    Now we are discussing what you think is a different flaw in the interpretation of the data. Namely that the shift in beak size of the G. fortis population was not due to competition of the large G. fortis with G. magnirostris, but due to the large G. fortis being outcompeted by small G. fortis.
    However, as to the first half of the argument (not due to competition with G. magnirostris), you yourself write:

    So, with two consecutive drought years resulting in very little T. cistoides, and its availability diminished due to the presence of the G. magnarostris, the large-beak G. fortis have to now compete with all of their fellow G. fortis for the available small and medium seed.

    So you agree that the presence of G. magnarostris factored into the diminished availability of T. cistoides.
    As to the second half of the argument (due to the competition by small G. fortis) clearly the authors of the paper agree. If there was no competition by small beaked G. fortis (i.e. if large and small beaked G. fortis could survive equally well on small seeds) then there would be no correlation of mortality with beak size.

    Thus, taken together, I really don’t understand what your specific disagreement with the conclusions of the authors is.

  51. 51
    PaV says:

    Bob O’H:

    Huh? Where’s your evidence that large-beaked G. fortis can’t feed on small seeds?

    The Grants wrote:
    “We have no feeding observations to indicate that [G. fortis] survived as a result of feeding on the typical components of the G. fuliginosa diet: the very small seeds of Sesuvium edmonstonei and Tiquilia fisca….Nevertheless, it may be significant…..” (btm p 225)

    These are not the same “small” seeds that the largeG. fortis normally eat.

    With that fact in mind, my point that the better interpretation is that the smallest G. fortis finches have an advantage rather than the large G. fortis having a disadvantage still stands.

  52. 52
    hrun0815 says:

    With that fact in mind, my point that the better interpretation is that the smallest G. fortis finches have an advantage rather than the large G. fortis having a disadvantage still stands.

    PaV, I really don’t understand what you are trying to say here. It is clear that you agree that the competition with G. magnarostris and the drought severely depleted T. cistoides seeds, thus taking away the food source that enabled large beaked G. fortis to survive the previous drought.

    Now we are down to explaining why G. fortis did not die uniformly (with respect to beak size) — like G. magnarostris — but why there was a rather strong correlation of mortality to beak size.

    You say: “Small beaked G. fortis finches had an advantage over large beaked G. fortis.” The authors say: “Large beaked G. fortis had a disadvantage over small beaked G. fortis.”

    I say: What is the difference? Can you explain?

  53. 53
    Bob O'H says:

    These are not the same “small” seeds that the large G. fortis normally eat.

    And what is your evidence for this? I couldn’t find anything in the paper about it.

    Bob

  54. 54
    PaV says:

    larrynormanfan:

    We had a thread here on Haldane’s Dilemna about a year ago. On that thread, I said two things: I said there was no way that Darwin’s finches could change beak sizes so quickly without there being a terrible decimation of the population; and, I said that if that happened, we would hear about it. Both those predictions have proven true.

  55. 55
    PaV says:

    Bob: read the second to the last paragraph on page 225.

    Earlier in the paragraph they said that the most G. fuliginosa-like members of the G. fortis were known to eat these seeds. The G.fuliginosa have long, narrow beaks.

    hrun0815:

    I say: What is the difference? Can you explain?

    It’s quite simple. The normal source of food for all the G. fortis are the “small”, “medium” and “large”, with the “small” seed being preferred by all, no matter the beak size. An alternative is the “Opuntia”, which was also not plentiful in 2004.

    With the scarcity of T. cistoides seeds, you had the entire population of G. fortis competing for the “small” and “medium” seeds. One would think that in such a situation, it would be equally likely for a large-beaked G. fortis to survive as a small-beaked G. fortis, which would result in a mean beak size that would be close to that of the previous year. (Notice that they say this on the first page: “In 1977, a drought on Daphne revealed that small seeeds are preferred when they are abundant, but when they are scarce, finches turn increasingly to large and hard seeds that only the large-beaked members of the population can crack.”) It’s for that reason that the authors suggest that the smallest-beaked G. fortis, with beaks siimilar to G. fuliginosa, had resource to “small” seeds outside the normal “small” seeds that G. fortis feeds on. They go onto mention that “it might be signifcant that two G. fuliginosa individuals were present on the island in 2004, and both survived to 2005.”

    You err in saying that the T. cistoides “enabled the large G. fortis to surive the previous drought.” Those “large” seeds didn’t enable them to survive; rather, it gave them a selective advantage that year over the small-beaked G. fortis. You’ll notice that after the first drought year the mean beak size increased. In the second year, with a presumably great scarcity of seed, the large-beaked finches “didn’t have” their selective advantage available to them (since the T. cistoides doesn’t reproduce in a drought year, and, of course the presence of G. magnarostris.), wheras the “smallest” of the G. fortis had access to seeds that the other, larger, G. fortis don’t feed on.

    So, by way of summary, in the first drought year the large-beaked G. fortis had a slight advantage, and mean beak size modestly increased. In the second drought year, there was little selective advantage for the large-beaked G. fortis while there was a real selective advantage for the smallest-beaked G. fortis, and so the mean beak size dramatically decreased. The better explanation would seem to be that the “smallest” beaked G. fortis had an advantage, rather than blaming it on competition from the G. magnarostris, which by the way were down to only four females and nine males by the beginning of 2005.

  56. 56
    PaV says:

    My last sentence in the last post should have begun this way:

    “The better explanation for the dramatically decreased mean beak size of the G. fortis in 2005 would seem to be……”

  57. 57
    Bob O'H says:

    Bob: read the second to the last paragraph on page 225.

    Earlier in the paragraph they said that the most G. fuliginosa-like members of the G. fortis were known to eat these seeds. The G.fuliginosa have long, narrow beaks.

    Err, yes. And where in that paragraph does it say that G. fortis with large beaks don’t normally eat small seeds? Nowhere.

    Now, I guess you could claim that G. fortis doesn’t eat small seeds, but you would have to explain the data in their reference 15, which shows the opposite.

    Bob

  58. 58
    hrun0815 says:

    PaV, I understand your summary of the facts. I do not understand why you classify this specifically as an ‘advantage for small beaks’ rather than a ‘disadvantage for large beaks’.

    Having a small beak or a large beak is mutually exclusive. Clearly from your writing I understand that you agree that in this particular case it was a liability for G. fortis to have a large beak: The large T. cistoides were depleted and their beaks did not allow them to switch to an alternative food source available to the G. fortis with a small beak.

    Thus, a large beak is strongly correlated with G. fortis mortality. To me, that seems to be a ‘disadvantage’.

    Of course, I also agree that in this particular situation having a small beak was an ‘advantage’. They are not mutually exclusive.

    In fact, I don’t see anywhere in the paper that the authors prefer one interpretation over the other. Clearly they think that being small beaked is an advantage, otherwise they wouldn’t write that ‘the only escape was available to the smallest, most G. fuliginosa–like, members of the G. fortis population […]’.

    So in the end, the only disagreement I can tell that you have with the paper is about to what extent the presence of G. magnarostris or the second drought year had an affect on the availability of T. cistoides seeds.

    Again though, it seems like the author agree with you or otherwise they would not write:

    Replicated experiments with suitable organisms are needed to demonstrate definitively the causal role of competition, not only as an ingredient of natural selection of resource-exploiting traits (12) but as a factor in their evolution (33).

    As you can see, the authors are well aware that further experiments are required to show causality of the competitor species and not just correlation.

  59. 59
    hrun0815 says:

    Note to my previous post:

    Of course, I also agree that in this particular situation having a small beak was an ‘advantage’. They are not mutually exclusive.

    Here I mean that having a large beak can be a ‘disadvantage’ while having a small beak can be an ‘advantage’– and thus not mutually exclusive. It is of course not possible for a bird to have a small and a large beak at the same time.

  60. 60
    PaV says:

    Bob O’H

    Err, yes. And where in that paragraph does it say that G. fortis with large beaks don’t normally eat small seeds? Nowhere.

    Err, then if the large-beaked G. fortis and smallest-beak fortis had access to the same seed sources, then how do you explain the change in mean beak size?

  61. 61
    PaV says:

    homerun 815: (Is that how many Bonds has?)

    Having a small beak or a large beak is mutually exclusive. Clearly from your writing I understand that you agree that in this particular case it was a liability for G. fortis to have a large beak: The large T. cistoides were depleted and their beaks did not allow them to switch to an alternative food source available to the G. fortis with a small beak.

    Thus, a large beak is strongly correlated with G. fortis mortality. To me, that seems to be a ‘disadvantage’.

    Not exactly: First, what I’m saying is that because of the presence of the G. magnarostris the selective advantage of having a large beak is lost for the G. fortis. Second, in the absence of this selective advantage, all the G. fortis must scramble for available resources—with none having any advantage over any of the others, save this: those with smaller bodies can obviously live on a smaller diet than a larger finch. Third, as the authors suggest, a selective advantage arises for those G. fortis with the very smallest beaks since they can take advantage of some very small seeds that aren’t part of the normal diet of the G. fortis. It would seem, then, that the better conclusion would be that change in mean beak size is due to the selective advantage of the “smallest”, G. fuliginosa-like members of the G. fortis that survived the first drought year rather than positing a disadvantage to the large G. fortis.

  62. 62
    hrun0815 says:

    First, what I’m saying is that because of the presence of the G. magnarostris the selective advantage of having a large beak is lost for the G. fortis. Second, in the absence of this selective advantage, all the G. fortis must scramble for available resources—with none having any advantage over any of the others, save this: those with smaller bodies can obviously live on a smaller diet than a larger finch. Third, as the authors suggest, a selective advantage arises for those G. fortis with the very smallest beaks since they can take advantage of some very small seeds that aren’t part of the normal diet of the G. fortis. It would seem, then, that the better conclusion would be that change in mean beak size is due to the selective advantage of the “smallest”, G. fuliginosa-like members of the G. fortis that survived the first drought year rather than positing a disadvantage to the large G. fortis.

    PaV, the authors are not concerned if the change in beak size is due to a selective disadvantage of the large beaked birds or a selective advantage of the small beaked birds. The result is the same: a strong correlation of mortality and beak size.

    But it seems that you have come full circle and now agree with the main conclusions of the authors: their thesis was that the presence of a competitor species that competes for a food source drove ‘character displacement’ in G. fortis.

    As you said (in First), due to the presence of G. magnarostris the large beaked G. fortis lost their selective advantage over others.

    You say (in Second), that all G. fortis must scramble for available resources where smaller bodied birds have a slight advantage, which the authors also found in the weak (but significant) correlation of mortality with body size.

    You point out (in Third), just as did the authors, that in addition to the large beaked birds losing their selective advantage, they also did not have the ability of the small beaked birds to survive. This is of course necessary for the mortality rate to correlate with beak size.

    So the authors are in full agreement with all of your three points (or the other way around).

    Your only point of contention is terming something a selective disadvantage for one group or selective advantage for the other. And I really don’t see in the paper that the authors necessarily disagree with you there either.

    Wow. I feel rather blessed. This is one of the very few times that an online discussion actually yielded a constructive result.

  63. 63
    Bob O'H says:

    Err, then if the large-beaked G. fortis and smallest-beak fortis had access to the same seed sources, then how do you explain the change in mean beak size?

    By quoting the paper:

    In 1977, a drought on Daphne revealed that small seeds are preferred when they are abundant, but when they are scarce, finches turn increasingly to large and hard seeds that only the large-beaked members of the population can crack (13, 15). Most finches died that year, and mortality was heaviest among those with small beaks (13, 16, 17).

    Also, when you write this:

    all the G. fortis must scramble for available resources—with none having any advantage over any of the others, save this: those with smaller bodies can obviously live on a smaller diet than a larger finch.

    It helps if you have some evidence that birds with larger beaks can’t eat smaller seeds. You still haven’t given any evidence that larger-beaked G. fortis can’t eat smaller seeds.

    I agree with hrun0815, you’re making progress. But you’re still not quite there. 🙂

    Bob

  64. 64
    hrun0815 says:

    Hi Bob, what do you think explains the strong correlation of mortality and beak size? Why did the larger beaked G. fortis die at a higher rate than the smaller beaked ones if not for food sources available to the small beaked ones that the large beaked ones can not exploit.

    Looking at table 2, beak size seems to be the strongest determinant of survival, more so than body size. And we know that the majority of birds died of starvation.

    Just trying to clear things up so we can all agree on the interpretation of the results of this study by the Grant’s.

  65. 65
    Bob O'H says:

    hrun0815 – it could simply be that they are less efficient in eating the seeds – they might be messier eaters of the seeds.

    Of course, this is speculation, but I haven’t seen any evidence that the larger-beaked birds can’t eat small seeds, and it’s something I’m sure would have been remarked upon if they did have a different diet. The text points towards them being able to eat smaller seeds, because it talks about the species feeding on smaller seeds and switching to the larger ones during drought.

    Bob

  66. 66
    hrun0815 says:

    hrun0815 – it could simply be that they are less efficient in eating the seeds – they might be messier eaters of the seeds.

    So then the disagreement between you and PaV is a matter of degrees? PaV suggests that large beaked fortis are generally unable to eat the smallest of the seeds whereas you say that they are able to do so, just not as efficiently as the small beaked fortis.

    I would suggest that who is right does not really have any bearing on the conclusions put forth in the paper, right? The key is that large beaked fortis have a selective disadvantage (or the small beaked fortis have a selective advantage) after the T. cistoides seeds were depleted by drought and G. magnarostris.

  67. 67
    Bob O'H says:

    hrun0815 – I guess you’re right. It’s a question of how accurately the paper, and the system, should be understood.

    Bob

  68. 68
    PaV says:

    Bob O’H:

    PaV:Err, then if the large-beaked G. fortis and smallest-beak fortis had access to the same seed sources, then how do you explain the change in mean beak size?

    Bob O’H answers:

    By quoting the paper:

    “In 1977, a drought on Daphne revealed that small seeds are preferred when they are abundant, but when they are scarce, finches turn increasingly to large and hard seeds that only the large-beaked members of the population can crack (13, 15). Most finches died that year, and mortality was heaviest among those with small beaks (13, 16, 17).”

    The quote you are using gives the reason that the beak size “increased” in 2003, and in 1977 (dramatically). But it doesn’t tell us anything about 2004. The ONLY thing it tells us about 2004 is that the large G. fortis DIDN’T have an advantage in 2004 because of the scarcity of T. cistoides. So, now all the birds are on the same playing field. Notice that in 1985, the G. fortis fed on the T. cistoides just as much as they did in 1977; and yet their mean beak size fell the next year. So, the T. cistoides is an advantage only in a drought year. We saw that in 2003. Now the T. cistoides is depleted. The advantage is gone. So, the large G. fortis DON’T have an advantage; we all agree; but that, alone, cannot explain why the beak size fell so dramatically in 2005.

    Of the four “lines of evidence” the authors give for the dramatic fall in 2005, the first two simply establish that, unlike 1977, in 2004 G. magnarostris presented competition for the large G. fortis; and the fourth simply points out that whereas in 1977 mean beak size went up, in 2004 it went down. But this simply means that the explanation for the 1977 shift obviously cannot account for the 2004 shift. So, they still haven’t explained anything. That leaves the third “line of evidence”. This “line” indicates that there was severe starvation, that Opuntia did not flower and was unavailable, which left the “only escape”, and that “only escape” was feeding on the tiniest seeds (or a small seed that the vast majority of G. fortis does not feed on); it is only the “smallest” G. fortis, the most G. fuliginosa-like, that feed on this seed. Voila. The explanation: the smallest G. fortis had a selective advantage in 2004, and mean beak size FELL in 2005. The largest G. fortis had an advantage in 1977, and the mean beak size GREW in 1978. Q.E.D. What more is needed?

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    hrun0815 says:

    So PaV, do you still think that Grant and Grant mis-interpreted any of their results?

    I was wondering if maybe you wanted to amend the original post to include your changed views. People might get a false impression if they only read the original post without wading through the over 60 comments.

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    Bob O'H says:

    PaV – I was specifically addressing your claim that large-beaked G. fortis didn’t eat small seeds. Yes, it’s a small point, but I have still to see any evidence from you to back up your claim.

    But, I think hrun0815 is right that you now seem to have understood the main point of the paper, and I think it might be good to add a note on the post.

    Bob

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