The beautiful thing about this paper is how simple the experimental design is. Basically: Step 1. Find a game reserve with giraffes in it (in this case, Lion Sands Game Reserve in South Africa, near Kruger National Park) Step 2. Build some browser-proof 2.2 meter-high fences around some tall acacia trees (giraffes can browse up around 4 meters, for obvious reasons). Wait through two growing seasons. Step 2.5. Fix the fences occasionally when elephants come by and smash them in a malicious attempt to spoil your research project. Step 3. Cut off some branches at various heights and measure the amount of leafy biomass. Do the same with some unfenced control trees. Compare. Here is one of the figures from the paper. Note: a "GBU" is a "Giraffe Browsing Unit", an overly technical term for "giraffe bite." So this chart is showing how much leaf biomass is available per bite for the giraffes, at 1 m, 2.5 m, and 4 m.Elissa Z. Cameron and Johan T. du Toit (2007). "Winning by a Neck: Tall Giraffes Avoid Competing with Shorter Browsers." The American Naturalist, 169, 130--135. DOI: 10.1086/509940 Abstract With their vertically elongated body form, giraffes generally feed above the level of other browsers within the savanna browsing guild, despite having access to foliage at lower levels. They ingest more leaf mass per bite when foraging high in the tree, perhaps because smaller, more selective browsers deplete shoots at lower levels or because trees differentially allocate resources to promote shoot growth in the upper canopy. We erected exclosures around individual Acacia nigrescens trees in the greater Kruger ecosystem, South Africa. After a complete growing season, we found no differences in leaf biomass per shoot across height zones in excluded trees but significant differences in control trees. We conclude that giraffes preferentially browse at high levels in the canopy to avoid competition with smaller browsers. Our findings are analogous with those from studies of grazing guilds and demonstrate that resource partitioning can be driven by competition when smaller foragers displace larger foragers from shared resources. This provides the first experimental support for the classic evolutionary hypothesis that vertical elongation of the giraffe body is an outcome of competition within the browsing ungulate guild.
As the paper notes, this has always seemed pretty "obvious" to most people -- especially if you have been to Africa and seen all the large herbivores, browsers and grazers of different shapes and sizes, living on one landscape by dividing up the food resource in minute ways (in fact, I noted that it was pretty obvious back in this 2005 PT post). But sometimes it's nice to experimentally test the obvious -- especially when creationists are going around denying it. Notes [1] Yep, he's apparently pretty clearly a traditional creationist of the Jehovah's Witness variety. He appeared in the German video Is the Bible Right After all? The theory of evolution lacks evidence. See links 1, 2, 3, 4. [2] Amongst a large about of debris in the form of creationist ranting-n-raving about unrelated issues.Despite popular acceptance that giraffes have long necks because of foraging competition during their evolution, no previous studies have experimentally investigated foraging competition between giraffes and smaller browsers. Simmons and Scheepers (1996) argued that there was little evidence that giraffes forage high in the canopy because of competition and suggested sexual selection as an alternate hypothesis. However, Woolnough and du Toit (2001) showed that giraffes achieve a bite-size advantage by feeding higher in the tree, and now we show that this is explained by the avoidance of competition with smaller browsers. While not resolving the controversy, our study provides the first experimental evidence that the giraffe's extremely elongated body form is naturally selected in response to competition from smaller browsing species.
27 Comments
Scott Simmons · 10 May 2007
"Step 2.5. Fix the fences occasionally when elephants come by and smash them in a malicious attempt to spoil your research project."
Now I understand the 'Elephants' line item in the Discovery Institute budget. I'd thought it might be code for Republican Party donations or somesuch ...
harold · 10 May 2007
Let me see if I understand the logic here...
A YEC guy makes some typical false statements claiming that scientists know less about giraffe evolution than is actually the case.
He doesn't necessarily say what his explanation for giraffe morphology is, but to his marginal credit, if he's YEC, we all know what it must be - God magically created giraffes in their current form, or created something very close, about 6000 years ago, then a couple of thousand years after that, all giraffes except the two that Noah took on the ark were killed in a flood, then giraffes disembarked the ark in Turkey after 40 days at sea, and that's how we got modern giraffes in Africa.
And the reason YEC is less crappy crap than ID is that this is a testable hypothesis. In fact, it's been tested - and proven false.
Okay, what's the testable ID explanation for the morphology of modern giraffes? How does a false understatement of scientific progress by a YEC creationist have anything to do with ID?
Nick (Matzke) · 10 May 2007
Lönnig claims to be doing ID in this paper, and gets indignant if someone suggests that ID is creationism. He might or might not be YEC himself, I don't know of any evidence either way (he does refer to millions of years in this giraffe paper, but that is not necessarily definitive).
Vyoma · 10 May 2007
How shocking. In other news, it was announced today that "ID" is no longer an acronym for "intelligent design," since that was an immature scientific theory. It is now understood to stand for "incessant dishonesty." In a closely related move, the Discovery Institute will be changing its name to Kentucky Fried Crapola and opening a service counter at a certain new museum, right next to the exhibit that explains how T. rex ate coconuts.
JohnW · 10 May 2007
Nick (Matzke) · 10 May 2007
Bob King · 10 May 2007
A good place to see the general flaws in JW creationism is here and in other online writings by Alan M. Feuerbacher
http://www.talkorigins.org/faqs/jw-evolution.html
Noturus · 10 May 2007
A J-dub that openly believes in intelligent design? Does that mean he accepts common decent? If so they have moderated quite a bit since they kicked me out for disagreement on that and other issues (such as a global flood), but then that was 5 years ago.
sparc · 10 May 2007
You will find quite some information on Lönnig's claims and the Max-Planck-scandal at evolutionsbiologen.de. Unfortunately, in German only.
Frank J · 11 May 2007
Frank J · 11 May 2007
Bob King:
A quote from the link you posted:
"Note particularly that Life selected a 1976 version Encyclopedia Britannica to support its position, because the 1983-84 versions did not say what Life's author wanted. Life was published in 1985."
Can someone please tell me why nearly everyone assumes that these people personally believe the nonsense that they peddle? Yes, I know about Morton's Demon, but can we at least admit that we have no basis to assume that it's operating in every single case.
molecanthro · 11 May 2007
sparc.
can you give me a rundown of the MPI scandal? I'm starting a PhD at one of the Max Planck Institutes in a few months and just wanted to know what it was about.
ScottN · 11 May 2007
_Arthur · 11 May 2007
What is the evolutionary relationship between okapis and giraffes ?
Aren't okapis some kind of midget giraffes ?
In other words, wouldn't an okapi skeleton, or an okapi fossil demonstrate that there are transitionals to the giraffe ?
sparc · 11 May 2007
molecanthro,
you will find a short description of the affair by Ulrich Kutschera at http://www.uni-kassel.de/fb19/plantphysiology/abbott.pdf.
Glen Davidson · 11 May 2007
There wouldn't be anything new about males and females partitioning a niche, presumably in order to reduce competition. This appears to have happened in various species, with an example in the following link:
http://www.blackwell-synergy.com/doi/abs/10.1111/j.1474-919x.2004.00377.x
Of course we don't know why males are taller than the females, perhaps it is indeed because of sexual competition. Taller and larger are both generally better for sexual competition, regardless of their selective adaptations to an environment.
My point about the possibility of niche partitioning is primarily that one ought not to automatically assume the reasonable sexual competition hypothesis, even when it's certain that both sexes of giraffe have a feeding advantage. Niche partitioning and sexual selection could both be working to make the taller males, to state the obvious.
The Simmons & Scheepers hypothesis manages not to explain the length of the female's necks, except as a kind of side effect. The latter might be reasonable enough, I suppose, if the costs of such height weren't substantial without a corresponding greater access to resources, or other advantage(s).
In all of these hypotheses, however, I wonder why the advantage of height in seeing predators isn't mentioned more often. I doubt that it could be the major force for selection, but as a selective advantage in a kind of "supporting role" I would think it could have an effect (probably difficult to distinguish from more important selective pressure, however).
Glen D
Nick (Matzke) · 11 May 2007
harold · 11 May 2007
It's perfectly possible that multiple factors could interact to amplify selection for extremely long necks.
Pure sexual selection usually refers to a case where the exaggerated trait is disadvantageous except in the context of attracting mates.
However, female preference for longer-necked males (or vice versa) and adaptation to exploiting higher vegetation are not mutually exclusive.
Steviepinhead · 11 May 2007
The patas monkey, one of the few monkey species that spends a substantial amount of time in a savannah-grasslands environment, displays an upright "lookout" or guard stance.
It's said that the principal lookout is typically the highest-status male in the group, though it's unclear--in brieg googling of the topic--how much this is based on observations of captive social groups as opposed to investigations in the wild.
But ethologists have been aware of the upright behavior for some time--I can remember my college professor in my anthro "Primate Cultural Behavioral" course, Dr. Suzanne Chevalier-Skolnikoff, discussing this back in the late '60s, early '70s.
This upright predator-location behavior has, of course, stimulated obvious speculation as to the advantages of the upright stance in another primate lineage.
Though I tend to agree with Nick that giraffe height is more likely due to feeding than predator-defense behavior.
Henry J · 11 May 2007
To put in my two cents - if there's several advantages to having a longer neck, it's apt to be quite difficult to verify the relative importance of the various effects, and it certainly isn't an "either/or" situation.
Henry
sparc · 11 May 2007
molecanthro,
one thing I forgot: During my PhD work I was two years at the Max-Planck-Institute for Biochemistry in Martinsried and I can assure you that Lönnig is the big exeption. Indeed, working there was really fun: open-minded collegues, quite some freedom to try your own science, best equipment, best funding, good seminars, lean administration etc. The only disadvantge: You will not be prepared for the reality at universities where you have to cope with old equipment, lack of money, teaching and a giant administrative overhead.
molecanthro · 12 May 2007
sparc,
thanks for that. yeah, i'm very excited about moving over to leipzig. i'll be at the MPI for evolutionary anthropology and it seems like an incredible place with loads of funding and great people. and i've heard that the main problem is that people that come out of there aren't prepared for 'the real world.'
i'm glad to hear that lonnig's institute is the exception. i'm surprised that they let that nonsense stay on the MPI website for so long. perhaps it's because the creationist threat hasn't been so bad in germany like it has been in the US and is becoming in the UK.
Paul Flocken · 12 May 2007
Is it also possible that the co-evolution mechanism is operating in addition to the others you have all mentioned? When the process started there were many low tier browsers so there was pressure on the plants to grow taller. That created the pressure for a tall browser. Then the giraffe's predecessors won the battle for the tall browser niche and the race between the plants and the giraffes was on, sealing the fate of the giraffes.
Sincerely,
Paul
Glen Davidson · 13 May 2007
Jeffrey K McKee · 14 May 2007
Nick (Matzke) · 15 May 2007
Kevin · 17 May 2007
"(note to creationists: read about homoerotic shifts), "
Christ now that would make their heads explode....