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Symbiosis
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Symbiosis is a close ecological relationship between the individuals of two different species.
These relationships can be cooperative, antagonistic, defensive, reciprocal, harmful, communal,
opportunistic, beneficial, or neutral. Symbiosis encapsulates the relationships that different
species of organisms have with each other: the good, the bad, and the ugly. These interactions
typically fall into one of three categories: mutualism, parasitism, and commensalism.
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Mutualism
A mutualistic relationship is one in which both organisms benefit from interacting with each
other. They cooperate with each other to achieve a desired outcome that will be beneficial to
both of them. Take the wrasse in the video clip for example. Cleaner wrasses have a mutualistic
relationship with the large fish they service. The fish at the cleaning station line up to get the
parasites picked off them; they are cleaned and free from harmful, blood-sucking parasites and
the cleaner wrasse gets a nice meal from the fish. There are certain species of ‘cleaner’ shrimp
that also perform this function. Both get something useful out of the deal, so the relationship is
mutually beneficial. Same thing is true for certain apes like baboons and chimps that comb each
other’s fur for ticks and lice. One gets a meal, the other gets cleaned.
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Mutualism occurs in the plant world as well, with pollination being the primary example of
mutualistic plant-animal relationships. Some more mutualistic symbioses for you to explore:
honey badgers and honeyguides, ants and butterfly caterpillars, zooxanthelles and coral.
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Parasitism
Parasitism is a relationship in which one organism benefits and the other is harmed. Parasitic
interactions consist of a parasite (the organism doing the harm) and a host (the organism being
harmed). In most cases, the parasite is smaller than the host. Parasitism is especially prevalent in
the micro-faunal world. There are thousands of species of ticks, mites, leeches, chiggers, worms,
mosquitoes, viruses, and bacteria that literally feed off their hosts. In many cases, parasitoids are
host-specific, and as a result have undergone amazing evolutionary changes to co-evolve with
their hosts. Although parasitism involves the pilfering of resources from one organism to
another, it is in the parasites best interest not to completely debilitate its host, otherwise it will
deplete its source of nourishment. When it comes to parasites there are many different types of
parasites, and many different ways that organisms weasel resources away from each other.
Brood Parasites
Take the brown-headed cowbird, a seemingly harmless creature common in woodlands and
suburbs across America. This cunning little critter is a brood parasite. Female cowbirds lie in
wait for unsuspecting female passerines (perching birds) to leave their nests and move in to lay
an egg in her nest while she is gone. When the resident female returns, she doesn’t know what
hit her and spends her time and energy brooding the intruding egg along with her own. Once the
eggs hatch the mother cares for all the babies, even the uninvited orphan. Oftentimes the
cowbird grows faster and stronger than the resident hatchlings and can out-compete them in the
nest, but the mother bird is devout and cares for it nonetheless. By parasitizing the passerine’s
nest, the female cowbird ensures that her offspring are cared for with minimal energy
expenditure on her part. While she doesn’t take anything directly from the mother bird, she is
indirectly parasitizing her energy and resources.
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Food Parasites
Parasites can parasitize an animal’s energy, directly by consuming their body fluids, and
indirectly by placing an energetic burden on them. That’s pretty bold, but some animals take
bold to an even greater level. There are some creatures in the animal kingdom that will literally
take the food out of another’s mouth! The parasitic jaeger, a predatory seabird, makes a habit of
stealing food. They soar around while terns and other seabirds are fishing and chase them in the
air to try and steal their food. Sometimes they are successful in capturing the food right from
their mouths, but in most cases they harass the hunters so much that they tire and drop the food
and the jaeger scoops up a free meal.
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Commensalism
A commensalistic relationship is one in which one organism benefits and the other organism is
unaffected, meaning it is neither harmed nor benefitted. The classic example of commensalism
is that of sharks and remoras. Remoras are scavenging fish that cruise around with sharks.
Sometimes they swim alongside sharks, and sometimes they hitch a ride, attaching themselves
via a suction-cup like appendage on their dorsal (top side) surface. The remoras wait for the
sharks to make a kill, and when they do, snap up bits and pieces of the bloody, shredded flesh as
the shark tears into it. They don’t pose any threat to the sharks, and don’t take the food from
them, merely eat the scraps. One could argue, however, that when the remoras attach themselves
to the shark, they create drag, which makes the shark have to work harder and expend more
energy to get around, thus the remora is indirectly parasitizing the shark. While the drag the
remora creates might be miniscule, the reasoning behind the theory is valid.
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Another example of a commensalistic relationship is between cattle and cattle egrets. Cattle
egrets are frequently found in fields foraging alongside herds of cattle. While the cows munch
away on grass, they stir up insects which the egrets snap up. This may be more reflective of a
truly commensalistic relationship as the egrets pose no real impediment to the cattle (or perhaps
the cows have to expend more energy to watch where they are going to avoid stepping on the
egrets!).
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The Big Picture
Symbioses are a dynamic way in which organisms of different species interact with each other.
These relationships can be positive or negative depending on their nature and the extent with
which the organisms are involved with each other. Below is a simple table to visualize the types
of interactions that symbiotic relationships between organisms embody.
Organism 1
Mutualism
Parasitism
Commensalism
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0 or n*
*n=neutral
Santana, E. 2012. "Symbioses" (OnLine) UntamedScience. Accessed Jun 06, 2012 at
http://www.untamedscience.com/biology/ecology/symbioses
For video see http://www.youtube.com/watch?v=zSmL2F1t81Q
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Organism 2
“Symbiosis” Guided Highlighted Reading for Summary
Directions: With a highlighter pen, follow the prompts of the teacher and highlight what the prompts instruct
you to highlight.
The teacher reads the following:
In lines #1-5, find and highlight the definition of symbiosis. (“Symbiosis is a close ecological relationship
between the individuals of two different species.”)
In lines #1-5, find and highlight the words that describe symbiotic relationships. (“…cooperative, antagonistic,
defensive, reciprocal, harmful, communal, opportunistic, beneficial, or neutral.”)
In lines #1-5, find and highlight the three main types of symbiosis. (“…mutualism, parasitism, and
commensalism.”)
In lines #6-15, find and highlight the definition of mutualism. (“A mutualistic relationship is one in which both
organisms benefit from interacting with each other.”)
In lines #6-15, find and highlight the assistance cleaner wrasses and the large fish provide each other. (“…they
are cleaned and free from harmful, blood-sucking parasites and the cleaner wrasse gets a nice meal from the
fish.”)
In lines #16-18, find and highlight three examples of mutualism from the plant world. (“…honey badgers and
honeyguides, ants and butterfly caterpillars, zooxanthelles and coral.”)
In lines #19-29, find and highlight the definition of parasitism. (“Parasitism is a relationship in which one
organism benefits and the other is harmed.”)
In lines #19-29, find and highlight examples of parasites. (“…ticks, mites, leeches, chiggers, worms,
mosquitoes, viruses, and bacteria….”)
In lines #19-29, find and highlight the reason that parasites don’t usually kill their hosts. (“…it is in the
parasites’ best interest not to completely debilitate its host, otherwise it will deplete its source of nourishment.”)
In lines #30-41, find and highlight the advantages that the female cowbird has in this relationship. (“…the
female cowbird ensures that her offspring are cared for with minimal energy expenditure on her part.”)
In lines #42-50, find and highlight how parasites feed on their host’s energy directly and indirectly. (“…directly
by consuming their body fluids, and indirectly by placing an energetic burden on them.”)
In lines #51-62, find and highlight the definition of commensalism. (“A commensalistic relationship is one in
which one organism benefits and the other organism is unaffected, meaning it is neither harmed nor benefitted.”)
In lines #51-62, find and highlight the classic example of commensalism. (…sharks and remoras.”)
In lines #63-68, find and highlight another example of commensalism. (“…cattle and cattle egrets.”)
In the chart, find and highlight the symbol used for a positive relationship. (+)
In the chart, find and highlight the symbol used for a negative relationship. (-)