New study supports Darwin's hypothesis on competition between species

Jun 14, 2011
Georgia Tech School of Biology assistant professor Lin Jiang displays a microscopic image of a protist species he used to support Darwin’s hypothesis that the struggle for existence is stronger between more closely related species than those distantly related. Credit: Georgia Tech/Gary Meek

A new study provides support for Darwin's hypothesis that the struggle for existence is stronger between more closely related species than those distantly related. While ecologists generally accept the premise, this new study contains the strongest direct experimental evidence yet to support its validity.

"We found that occurred more frequently and more rapidly between species of microorganisms that were more closely related, providing strong support for Darwin's theory, which we call the phylogenetic limiting similarity hypothesis," said Lin Jiang, an assistant professor in the School of Biology at Georgia Tech.

The study was published online on June 14, 2011 in the journal . The work was supported by the National Science Foundation.

Jiang and his team -- Cyrille Violle, formerly a postdoctoral fellow at Georgia Tech currently at the Centre d'Ecologie Fonctionnelle et Evolutive in Montpellier, France, and Georgia Tech biology graduate student Zhichao Pu -- conducted experiments with 10 common ciliated protist species in artificial, simplified ecosystems called microcosms. Diana Nemergut, an assistant professor in the Institute of Arctic and Alpine Research and the Environmental Studies Program at the University of Colorado at Boulder, helped the team generate a family tree of the 10 microorganisms to determine how closely related the species were.

"We selected bacterivorous ciliated protist microorganisms for this study because they rapidly reproduce, allowing us to examine species co-existence over multiple generations in a closed system during a period of a few weeks, which wouldn't be possible if we were testing the hypothesis with plants or animals," said Jiang.

The researchers set up 165 microcosms that contained either an individual protist species or a pairing of two species, along with three types of bacteria for the organisms to eat. They collected weekly samples from each and examined them under a microscope, recording the presence or absence of species. After 10 weeks, the researchers estimated the density of the protist species in each microcosm.

The study results showed that all species survived until the end of the experiment when alone in a microcosm. However, in more than half of the experiments in which protists were paired together, one of the two species dominated, leading to the extinction of the other species.

The researchers found that the frequency and speed of this extinction process -- called competitive exclusion -- was significantly greater between species that were more closely related. In addition, in microcosms where both competitors coexisted for the duration of the experiment, the abundance of the inferior competitor was reduced more as the phylogenetic relatedness between the two competitors increased.

The study also showed that the frequency of competitive exclusion was significantly greater between species that had similar mouth sizes.

"We documented the mouth size of each species because there is some evidence that this morphological trait affects the selectivity and uptake rate of prey particles, and we thought that similarity in mouth size might translate into the exploitation of similar bacterial resources and result in competitive exclusion," said Jiang.

While they found that phylogenetic relatedness predicted the likelihood of coexistence better than mouth size, the results suggest that other traits involved in resource uptake may also be important predictors of the outcomes of competitive interactions in ecological communities.

"This study is one step toward a better understanding of how phylogenetic relatedness influences species interactions," said Jiang. "We hope our experimental validation of the phylogenetic limiting similarity hypothesis in will encourage other ecologists to conduct additional studies with other types of organisms to further validate Darwin's hypothesis."

The phylogenetic limiting similarity hypothesis is just one of the many ideas Darwin published in his 1859 book called "The Origin of ." In this book, Darwin introduced his scientific theory that populations evolve over the course of generations through a process of natural selection. The book presented a body of evidence that the diversity of life arose by common descent through a branching pattern of evolution.

Explore further: Japan's new whaling plan will prove hunt is science: negotiator

Related Stories

Why do some queen bees eat their worker bee's eggs?

Dec 04, 2006

Worker bees, wasps, and ants are often considered neuter. But in many species they are females with ovaries, who although unable to mate, can lay unfertilized eggs which turn into males if reared. For some ...

Recommended for you

User comments : 27

Adjust slider to filter visible comments by rank

Display comments: newest first

kevinrtrs
1 / 5 (21) Jun 14, 2011
Unfortunately, for all it's support of Darwin's theory, it still cannot confirm that the diversity of life arose by common descent from a single ancestor.
All of biological life is subject to identity and environmental stress. This identity is determined by the make-up of it's DNA [and pseudo genes] which has enough flexibility to adapt to a certain amount of physiological/environmental stress. Once the environmental stresses exceed it's built-in capability to adapt, the organism DIES. What one can say is that once the environmental stress requires that the organism change it's identity in order to carry on surviving conditions that are unsuited to it's make up, the organism DIES rather than change identity. OR more succinctly : Any attempt to change identity results in DEATH. We observe this every day. There is no exception to this observation.
This simply means that Darwin's theory of common descent is invalid because that theory contradicts our own repeated, confirmed observations
Peteri
5 / 5 (13) Jun 14, 2011
Kevenrtrs

Carefully reading through your statement it would appear that, rather than providing us with any argument against the process of evolution by natural selection, you are in fact describing the very process by which it occurs!

You are basically saying that an individual organism who's genetic make-up reduces their chances of surviving environmental stresses (be it disease, predators, changes in the climate, etc) have a reduced chance of surviving.

The only thing you didn't quite get around to saying is that this reduced survival rate reduces the organism's chances of successfully breeding and passing its genes to any offspring, whereas organisms possessing genes that enable them to survive the same environmental stress get to breed and pass on their genes.

So congratulations kevenrtrs, you should feel proud of yourself - you've pretty much, at least partially, re-stated the basic theory of evolution by natural selection - Darwin would be proud of you!
Vendicar_Decarian
0.4 / 5 (40) Jun 14, 2011
Childish poppycock.

Organisms are regularly seen adapting their genetic "identity" there DNA sequences in response to environmental stress.

The development of antibiotic resistance in bacteria is a prime, but not exclusive example.

"OR more succinctly : Any attempt to change identity results in DEATH. This identity is determined by the make-up of it's DNA..." - Tard of Tards

Peteri
3.8 / 5 (6) Jun 14, 2011
Vendicar Decarian

Although I agree whole heartedly with most of your sentiments on subjects such as evolution and climate change, insulting people by calling them "Tard" does nothing to further your arguments. In fact, as well as appearing childish, it makes you look as bigoted as the people you are denouncing.

Furthermore, by insulting them in this way you do nothing to help the rest of us who are trying to have a reasoned debate with these people - it just serves to confirm in their own minds that we don't have a valid argument and are desperately resorting to playground insults in an attempt to refute their ideology.

Please desist with the insults.
Donutz
5 / 5 (4) Jun 14, 2011
Peteri: You're new, aren't you? You can't have a "debate" with kevin. He doesn't debate. He ignores responses. He's ignored yours, too.
gmurphy
5 / 5 (2) Jun 14, 2011
@Donutz, Peteri was responding to Vendicar_Decarian. I second the sentiment expressed by Peteri, fwiw.
Glyndwr
5 / 5 (2) Jun 14, 2011
Tard is offensive to those having to care like me for severely disabled relatives.

Red and grey squirrels in Britain is a decent example of closely related species causing each other to go extinct (except man has a hand in this scenario ;) )
jsa09
4.5 / 5 (2) Jun 14, 2011
@Vendicar_Decarian the animals do not adjust their DNA as a result of stress to become immune to antibiotics. Although anthropomorphizing what does happen would make it appear so.

Kev is right - the ones that cannot survive die. What kev fails to notice is that not all animals are the same even. Even brothers and sisters are different. Therefore, if it doesn't kill you, you survive. Those that survive produce offsping. Offspring have some characteristics of their parents hence evolution.

@peteri - Yep kev restated the evolution effect while trying to undermine it. Shows that after making all the numerous contributions to these topics, trying to promote a young Earth and "god dun it" attitude he may yet get the picture.

If he does, he will immediately reject it, because his fear of death is too powerful for him to learn to live with evolution.
Deesky
5 / 5 (4) Jun 14, 2011
Kev, the accidental Darwinist!
Ethelred
5 / 5 (2) Jun 15, 2011
@Vendicar_Decarian the animals do not adjust their DNA as a result of stress to become immune to antibiotics.
Actually VendiTARD has a point. Not in his execrable behavior but in his statement on stress.

Stress causes the release of numerous hormones and those often include chemicals that increase the rate of mutations. No organism has changed their DNA in any particular manner in order to adapt. They have changed their rate of mutation which increases both the chance of an improvement and a chance of a problem. Problems are more probable in species that are in tune with their environment. But when a species is under stress due to changes in the environment change has a better chance of being an improvement since staying the same is the path to extinction. Stress drives change and organisms have evolved to change faster when under stress.>>
Ethelred
5 / 5 (2) Jun 15, 2011
Vendicar often makes good posts that are marred by a severely bad attitude. He has been doing this for years on many sites. Apparently even going so far as to suggest that President Dumbass should die. That would have made Vice President Mad Dog the President thus showing Vendicar is not very good at politics.

It would be really nice if both Kevin and Vendicar made major changes in behavior. In the meantime I give VD a one every time I seem him use TARD in a post. No matter how good the rest is. Then again I call Marjon an idiot rather frequently. But I have given up on Marjon. He is just a Troll. Kevin seems to believe his nonsense. He too is a Troll since he refuses to debate.

Which is better?
Marjon's infinite posts that do not constitute a reasoned debate.
Kevin's refusal to respond in anyway at all.

Both are childish and troll like. But Kevin wastes less space.

Ethelred
Donutz
5 / 5 (1) Jun 15, 2011
@Donutz, Peteri was responding to Vendicar_Decarian. I second the sentiment expressed by Peteri, fwiw.


Yah, I know. I was referencing peteri's desire to have an "honest debate" with kevinrts. Not gonna happen. Many of us have tried to have that debate at one time or another. We grow out of it.

As I've pointed out to KR numerous times, he should start by showing factual, theoretical, or logical support for the basic premise on which his entire belief system is based -- a particular deity who is responsible for a particular set of books. Seen anything like that? Me neither.
Vendicar_Decarian
0 / 5 (34) Jun 15, 2011
"Tard is offensive to those having to care like me for severely disabled relatives." - Glyndwr

I've been there. Done that. Got the t-shirt.

Vendicar_Decarian
0 / 5 (34) Jun 15, 2011
"That would have made Vice President Mad Dog the President thus showing Vendicar is not very good at politics." - Ethelred

Oh, I clearly stated that mad dog should have been tortured and executed as well.

"I give VD a one.." - Ethelred

Oh... The humanity... The humanity.... How can I stand the ignominy?

Vendicar_Decarian
0.1 / 5 (36) Jun 15, 2011
"Furthermore, by insulting them in this way you do nothing to help the rest of us who are trying to have a reasoned debate with these people" - Peteri

There are those who are beyond reason and beyond redemption.

For them death is the only cure.
Vendicar_Decarian
0 / 5 (34) Jun 15, 2011
"@Vendicar_Decarian the animals do not adjust their DNA as a result of stress to become immune to antibiotics. Although anthropomorphizing what does happen would make it appear so." - Isa09

I did not say animal, I said organism, which is a little more general.

I don't think there is actually an adequate term for a identifiable biological entity that is undergoing evolutionary change. The term "species" comes close of course, but doesn't mesh with the concept well.

I will coin a term for such a thing and rephrase.

The term is "evolope".

Organisms are members of evolopes, and evolopes are regularly seen adapting their genetic "identity" there DNA sequences in response to environmental stress.

aroc91
not rated yet Jun 15, 2011
MY NAME KEVIN, I NO UNDERSTAND WHAT MUTATION MEAN
Ethelred
5 / 5 (1) Jun 15, 2011
Oh... The humanity... The humanity.... How can I stand the ignominy?
Obviously you will have no more trouble than you do being considered a complete ass by nearly everyone that sees your posts. You have been doing that for years.

Just because you sometimes make posts that are actually good doesn't mean that you don't have a rather large tendency to act the utter ass.

Basically your a Troll that can't help making the occasional relevant comment. Try changing the balance to less Troll and more relevancy.

Ethelred
Ethelred
5 / 5 (1) Jun 15, 2011
I did not say animal, I said organism, which is a little more general.
Fine replace animal with organism. Either way it would still be right.

I don't think there is actually an adequate term for a identifiable biological entity that is undergoing evolutionary change.
Organism will do just fine. I use it frequently as some organism are not members of sexually reproducing species.

The term "species" comes close of course, but doesn't mesh with the concept well.
Doesn't work with any cloning species and there are more then most think.

The term is "evolope".
I think I will pass on that. ALL organisms have mutations and thus all are subject to evolution.

and evolopes are regularly seen adapting their genetic "identity"
The only thing they do is produce stress chemicals. The adaptation is through extinction of the failed changes.

Ethelred
Vendicar_Decarian
0 / 5 (34) Jun 16, 2011
No, an evolope is a set of related organisms, and as such evolves through the alteration of the sets DNA over time.
Vendicar_Decarian
0.2 / 5 (36) Jun 16, 2011
"Basically your a Troll that can't help making the occasional relevant comment" - Ethelred

You will find that all my posts are relevant, unless they are just intended to be humorous.

They largely illustrate how the topic being discussed shows how Conservative Liedeology is a failure.

Since you are a Ideological Conservative, I see your kind of irritation everywhere.

I must say however, that you seem to be more of a member of the reality based community than most of your Conservative Brethren.

That is good, because it actually means that you have a few brain cells left.

Ethelred
5 / 5 (1) Jun 16, 2011
No, an evolope is a set of related organisms
Which leaves out clonal organisms. They evolve too. Just very slowly.

and as such evolves through the alteration of the sets DNA over time.
All reproducing organisms evolve over time. Some just take a long time and others have few visible changes.

Besides the word sucks. Too much like envelope.

Ethelred
Ethelred
5 / 5 (1) Jun 16, 2011
You will find that all my posts are relevant, unless they are just intended to be humorous.
Then you are in serious need of an elbow transplant.

They largely illustrate how the topic being discussed shows how Conservative Liedeology is a failure.
Unfortunately they largely show a lack of humor and a lack of manners. A bad combination. Missing one of those is not a handicap on-line but both at once is just for Trolls.

Since you are a Ideological Conservative, I see your kind of irritation everywhere.
I think that remark shows just how deranged your thinking can be if anyone has the temerity to disagree with you. That is first time anyone here has made such an ignorant accusation.>>
Ethelred
5 / 5 (1) Jun 16, 2011
I must say however, that you seem to be more of a member of the reality based community than most of your Conservative Brethren.
This is entirely because I am smarter than you. You have to be quite bereft of observational skills to call me a conservative of any kind besides Conservationist. Perhaps an elbow transplant will not be enough. The whole nine yards may be needed. Or just a brain transplant.

That is good, because it actually means that you have a few brain cells left.
Which says little for you since you are vastly my inferior in political competence. Only a complete imbecile would think that VP Mad Dog would be an improvement on President Dumbass and even that hypothetical imbecile would have noticed that Conservatives aren't in the habit of calling Chaney and Bush by those very accurate names.

Ethelred
Shakescene21
1 / 5 (1) Jun 19, 2011
I'm not sure that this experiment properly controlled for the fact that closely related microorganisms are more likely to occupy similar ecological niches. In my opinion, the ecological niche is much more important than the closeness of the genetic relationship. In an extreme case, if there were two closely-related species, but Species A was specialized to eat Bacteria A while species B was specialized to eat Bacteria B, the two Species would probably be better off together, because of a more balanced bacteria population.
Shakescene21
1 / 5 (2) Jun 19, 2011
VD illustrates a serious problem for Science, namely that some scientists are jerks at the personal level. Not only does it make a lot of Physorg discussions less productive, but in the wider world it often turns the public against scientists. I have witnessed two forums on climate change where an arrogant progressive was paired against a likeable global warming skeptic, and after 10 minutes the bulk of the crowd was so turned off by the arrogant scientist that he lost most of them despite the validity of his facts. No matter how brilliant a scientist may be, in the long run she needs to get along with people.
malapropism
not rated yet Jun 19, 2011
I'm not sure that this experiment properly controlled for the fact that closely related microorganisms are more likely to occupy similar ecological niches. In my opinion, the ecological niche is much more important than the closeness of the genetic relationship.

IMHO you've misunderstood the point of the experiment. The very fact of the test species being more (or less) closely related is what renders the ecological niche occupied by the test species as putting more (or less) competitive pressure on them. This competitive pressure is what created the conditions for extinction of one of the species when any two were put together in a microcosm ecosystem.

What was interesting is that more closely-relatedness brings about a quicker resolution to the competition, thereby giving further evidence to the theory.

@Kev: Btw, they weren't testing the theory that all species may have arisen from a single common ancestor, although this experiment does lend some weight to it.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.