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Symbiosis vs. Parasitism (definitions)

Segnosaur

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A long time ago (in a galaxy far far away), I remember learning the definition of symbiosis involved 2 species interacting with each other in a mutually beneficial way. Parasitism was defined as something all together different (one species benefits from the interaction, the other is harmed.)

However, I recently came across a different description. For example, Wikipedia defines symbiosis as the interaction between 2 species, regardless of whether one or both of the species is harmed. Thus, "parasitism" is simply another type of symbiosis, and what I had been classifying as symbiosis was actually mutualism.

So, my question is: Was I remembering the definition of "symbiosis" incorrectly (or was I taught incorrectly)? Or has the definition been changed somehow in the past decade or 2 since I last took biology to make it more inclusive?

http://en.wikipedia.org/wiki/Symbiosis
 
You didn't get your definitions from Hal Clements' novel "Needle" did you?
It's where I got mine. Which are like yours.
 
Humans using yeast for creating bread or alcohol, killing yeast cells in the process, is in one sense parasitic The other side of the coin is that yeast have tricked humanity into growing vast tracts of land in wheat, grapes and barley for the purpose of feeding yeast and radically increasing their population.

Who is the parasite here ?

Humans lose a fraction of the nutrient value of their agriculture, but gain a more digestible or better preserved, or pleasurable foodstuff.
The individual yeast cells lose, but the species is extensively propagated beyond any rational level and the species survival is certainly enhanced by human management

The neutral meaning is "symbiosis" is justified. Any analyses of parasitism are based on subjective and therefore biased evaluations of benefit/loss between species.

Even HIV may help primates select for a a more robust genome describing a more effective immune system.

"Sufficient unto the day is the evil thereof " - Cicero
 
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You didn't get your definitions from Hal Clements' novel "Needle" did you?
It's where I got mine. Which are like yours.
Nah, its just the old definition that I remember from High school/university biology class. (But, since I don't work in the biological sciences, its possible that my knowledge is faulty.)
 
Humans using yeast for creating bread or alcohol, killing yeast cells in the process, is in one sense parasitic The other side of the coin is that yeast have tricked humanity into growing vast tracts of land in wheat, grapes and barley for the purpose of feeding yeast and radically increasing their population.

Who is the parasite here ?
I don't think this counts as either symbiosis or parasitism.

The definitions I have come across suggest that individuals of the species involved in the relationship have "close and often long-term interactions". I don't think simply feeding on another organism qualifies it as being parasitic because the relationship isn't particularly close.
 
The issue is that you're trying to put biological interactions into boxes. While this is useful in some cases, it's almost universally simplification, and there's always going to be fuzzy boundaries. I've often questioned the value in doing so; it's seemed to me for a long time that such attempts have held us back more than anything else.

As for parasitism and symbiosis, the OP's definitions are correct as far as I recall. However, they're limited to individual organisms, not populations--meaning that something that's good for the population but bad for the organism is called parasitism or predation, while something that's good for the organism but destroys the population would still be called symbiosis or something else which slips my mind at the moment. We tend to think of predation and parasitism as bad things, but in an evolutionary perspective they're just interactions; similarly, while we tend to consider symbiosis as a good thing evolution doesn't really care.
 
Hmmm... after a little more research, I found a few references that support my original definition. (So maybe my memory isn't faulty after all.)

From: http://science.howstuffworks.com/environmental/life/evolution/symbiosis1.htm
The traditional definition of symbiosis is a mutually beneficial relationship involving close physical contact between two organisms that aren't the same species. Most biologists still adhere to this definition. Some biologists, however, consider any interspecies relationship involving frequent close contact to be symbiosis, regardless of which of the organisms benefits.

From: http://dictionary.reference.com/browse/symbiosis
a. the living together of two dissimilar organisms, as in mutualism, commensalism, amensalism, or parasitism.

b. (formerly) mutualism ( def. 1 )
 
Symbiosis is three different ways a pair of creatures interact.

Mutualism is where both creatures benefit eachother.
Commensalism is where one is benefited while the other is neither benefited or harmed.
Parasitism is where one is benefited while harming the other.

ETA: I'd never heard of Amensalism, but it's where one is harmed while the other isn't benefited. Sounds rare.
 
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Here's the definitions I gave to my junior agriculture class.

A parasite is a eukaryotic organism (that is, not a virus or bacterium) which lives on or in another organism to the detriment of that organism
Examples include liver fluke, mange mites and ringworm
A commensal is an organism which lives on or in another organism without causing any harm to that organism
Examples include harmless skin bacteria
A symbiont is an organism which lives on or in another organism which is necessary to the health of that organism
Examples include bacteria in the mammalian intestine which are essential to the digestive process
A saprophyte is an organism (usually a fungus or bacterium) which lives on dead, decaying organic matter
Some saprophytes (e.g. Bacillus licheniformis) and commensals can become pathogens under certain circumstances – “opportunist pathogens”
A scavenger is a larger organism (bird or mammal) which lives on dead meat (e.g. road kill or the leavings of a predator)
A predator is a larger organism which kills to eat
A livestock farmer is a predator who is very, very organised


Rolfe.
 
The issue is that you're trying to put biological interactions into boxes. While this is useful in some cases, it's almost universally simplification, and there's always going to be fuzzy boundaries.

Exactly this. It's the same with so many biological definitions. Try getting a hard definition of life or species that everyone can agree with. It's the same with something like symbiosis. Any single work may use a particular definition, but it won't necessarily be exactly the same as the one used somewhere else. Sometimes it might be because a particular definition is more useful in a given context, but a lot of the time it's down to little more than personal preference.

So I wouldn't say that Wikipedia or Segnosaur are wrong, or that the definition has changed. It's simply that they were written/taught by different people who happened to be using different, but still fairly similar and mutually understandable, definitions.
 
Side bar
This really doen't make sense.

How do you think this would work? especially given the long slow development of AIDs.

It would work exactly the same as any other natural selection.
http://www.sciencedaily.com/releases/2010/05/100505133250.htm

How does that not make sense ?


I don't think this counts as either symbiosis or parasitism.

The definitions I have come across suggest that individuals of the species involved in the relationship have "close and often long-term interactions". I don't think simply feeding on another organism qualifies it as being parasitic because the relationship isn't particularly close.

So you don't believe that centuries of humans interacting with yeast, represents symbiosis ? What about humans agrarian adaption of fruits, grains, domestic animals? It has to do with interacting species not individuals. These are of course examples of symbiosis.
 
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Cuddles said:
So I wouldn't say that Wikipedia or Segnosaur are wrong, or that the definition has changed. It's simply that they were written/taught by different people who happened to be using different, but still fairly similar and mutually understandable, definitions.
Yup. The important thing is to be consistent with your application of these definitions--at least that way when you use "symbiosis" we'll know what you mean. It's not really possible to create a "correct" definition.

stevea said:
These are of course examples of symbiosis.
Depends. If we kill the organism and eat its seeds, it can be argued to be a form of parasitism, or commensalism (if it's an annual species and will die anyway). Personnally I wouldn't feel comfortable applying the term sybmiosis to any situation where the individual organism is harmed but the population is helped; it degrades the already badly defined term into a term that can be applied to nearly anything.
 

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