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Symbiotic Relationships in Nature
The word symbiosis can be broken down into syn, meaning with, and biosis, meaning living. From those meanings, the definition of a symbiotic relationship can be inferred. It is an intimate and sometimes long-term interaction between two different biological species. Symbiotic relationships can be broken down into three categories of relationships. The three categories are mutualism, commensalism, and parasitism. The three categories of symbiosis can be looked at as effects. Mutualism has a positive-positive effect. This means that each partner in the relationship is mutually benefitted. Commensalism has a positive-neutral effect. This means that the commensal, or they partner that benefitted, benefits and the host is not affected in any way. Parasitism has a positive-negative effect. This means that one partner benefits and the other partner is harmed. This paper will look at mutualism, commensalism, and parasitism and examples of the relationships that can be found in nature.
Mutualism is when both of the species, or partners, benefit from their interactions. An example of a mutualistic relationship is the one between plants and mycorrhizal fungi. The mycorrhizal fungi form these relationships with the plants after entering their roots. There are some plants that depend on the fungi to survive. When mycorrhizal fungi enter the roots of the plant they begin to make hyphae. Hyphae are small, branch-like structures. They increase the area of absorption so the plant can take in more water and nutrients. Mycorrhizal fungi can also send out compounds that help to decompose organic matter that they then absorb. Since this is a mutualistic relationship the mycorrhizal fungi also benefit. The fungi give the plants nutrients and water and the plants let the fungi acquire their food, which is sugar, directly from the plant cells (Wallace, 2004).
Another example of mutualism would be the relationship between the clown fish and the sea anemone. A sea anemone comes in many colors and it attracts many fish. When the fish come towards the “flower” the sea anemone stings the fish with its tentacles and eats the fish. The clown fish, however, is able to build up immunity to the sting of the sea anemone. Because the sting doesn't affect the clown fish, it hides in the sea anemone. The sea anemone allows the clown fish to hide in it because the clown fish attracts larger fish, which the sea anemone will kill and eat (Silverstein, 1998). Another benefit of letting the clown fish hide in the sea anemone's tentacles is fresh oxygen. The sea anemone is stationary and the oxygen becomes stale and that make the sea anemone sick. While the clown fish is hiding, it moves its fins and that stirs the oxygen giving the sea anemone fresh oxygen (Silverstein, 1998).
The sea anemone doesn't only have a partnership with the clown fish; it also has one with the hermit crab. When the hermit crab wants to strike up a partnership, it picks up the sea anemone and begins to carry it on its back. The sea anemone hides the hermit crab from predators and stings the predators that get too close. The hermit crab will catch food and share some of it with the sea anemone. The movement also allows the sea anemone to catch more food that it would if it were stationary(Silverstein, 1998).
Commensalism is when one partner benefits while the other partner is neither harmed nor benefitted. An example of commensalism is the relationship between manta rays and remoras (Corral Reef Connections). Manta rays are some of the largest fishes. They eat small prey such as fish and crustaceans. Sometimes, some of the manta ray's food will avoid be eaten by the ray only to be eaten by the remora. The remora is a fast swimming fish that has a suction disc which allows them to attach themselves to hosts like the manta ray (CRC). When the manta ray begins to eat, the remora will go behind a pick up whatever scraps the ray leaves behind (CRC). Because the remora benefits and the manta ray is neither harmed nor benefitted their relationship is a form of commensalism.
The relationship between cattle egrets and livestock is another example of commensalism. When livestock such as cows or horses move, they rouse insects that were previously hidden in the grass. When these insects are flying out of the grass the cattle egret eats them. In this relationship the cattle egrets benefit by eating the insects that the livestock stir up, while the livestock do not benefit, nor are they harmed.
Parasitism is when one partner benefits at the expense of the other partner during their interactions. It is complex and has been seen in all animals and plants that are known (Calow, 1998). Examples of parasites are mistletoe plants. All mistletoes, no matter what species, are parasites. They are “aerial parasites of tress (Glatzel, 2008).” They attach to a host branch, must defeat the host plant's defenses, and gain access to the nutrients and water they need to be successful. The main resource the mistletoe competes for is water. It has to compete with all the other branches and leaves for the water. Some people wonder why the mistletoe and the tree's relationship is not considered as mutualistic, or why the mistletoe is not considered as another branch. The reason that neither of these is possible is because the mistletoes do not “contribute significantly to the photosynthetic gain of the host tree (Glatzel, 2008).” Since the mistletoes do not contribute to the host tree, but they still take water and nutrients from the host tree, they are considered parasites because they are benefiting at the expense of the host tree.
Another form of parasitism can be found in nematodes and plants. While there are many different species of nematodes, the mechanisms of how the parasitize the plants are basically the same. The nematodes all have a stylet and are obligate, which means they must feed on a plant once in order to complete their life cycle (Nematode Parasite Page). They obtain nutrients from living cells of leaves, stems, or roots. Plant parasitic nematodes can be placed into two categories: endoparasites and ectoparasites. Endoparasites feed on the plant from the inside and ectoparasites feed on the plant from the outside (NPP).
Nematodes are also parasites of animals. There are many different species and their feeding habits are diverse. What they eat, however, is not diverse. They will consume blood, digestive, lymph, mucosa, secretions and hepatic tissues. An example of a parasitic nematode in an animal is the hookworm in humans (NPP). When the hookworm gets into the human they go straight to the intestines. From there it hooks its latch into the host and begins to suck the host's blood. When there is only a small amount of hookworms in the human, the infection is considered to be light and will have no symptoms (NPP). The symptoms from a heavy infection can be very serious. The symptoms can include anemia, loss of appetite, weight loss, diarrhea, and abdominal pain. There are also side effects for these symptoms. They can include tiredness, difficult breathing, enlargement of the heart, and an irregular heartbeat (NPP).
As can be seen from all of the examples, symbiotic relationships can be found in practically every niche of the world. They can also be seen in all groups of life on the planet. Each of these relationships contributes to the understanding of each their respective ecosystem.
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