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Symbiosis Mutualism, Commensalism, and Parasitism

Hippopotamus San Antonio Zoo Photo Credit Zack Neher 2

Photo: Zach Neher; http://thenaturalworld1.blogspot.com/2013/02/animals-of-san-antonio-zoo-ungulates.html


Symbiosis can be described as a relationship when two organisms of different species benefit from the presence of each other. Each organism contributes something to the relationship and receives something beneficial in return. These relationships can occur between plants and animals and a combination of the two. Evolutionary biologists believe this relationship is driven by natural selection in which their survival is determined by these traits they possess that help them survive.

3 Main Types of Symbiosis[]

1.     1. Mutualism is a relationship where both organisms in the relationship benefit. Many zoos will place African cichlid fish in their hippo exhibits not only because they both exist in their wild habitats together, but because of their natural relationship where the cichlid fish clean the hippos bodies and mouth which then provides them with a great source of nutrition. 

2.     2.  Commensalism exists when one organisms benefits and the other organism isn’t affected – positively or negatively. A common example is the elephant and the egret. As the elephant walks around throughout the day, many egrets will follow them around. Their large feet kick up many bugs as they trample through the grasslands or dirt. The egrets simply follow close behind them and catch the bugs as they spring up into the air. The elephants don't care that the egrets are following them nor does it harm them in any way. They are simply going on with their daily activity and the egrets are benefiting off of their activity. 


Photo accessed via: http://www.astronomy-images.com/day-images/Africa/elephants__with__cattle__egrets.htm)

3.     3.  Parasitism: When many people hear the word “parasite”, they think of the obvious tapeworm, roundworm, mosquitos or leeches. But the tomato hornworm and braconid wasp is an excellent example of a parasitic relationship. A parasitic relationships exists when one species benefits while the other one is harmed. The parasite needs to host to survive and therefore typically does not kill its host. For example, the common tick which feeds off of the blood of its host animal. The tomato hornworm is a fairly common gardening pestand is an exception to the rule. The braconid wasp lays its eggs on caterpillar and causes it to die as it goes through its pupation. Its inner organs have basically been digested by the wasp larvae in order for it to survive. Gardeners may consider the death of the hornworm beneficial to them as it decreases the amount of crop loss. 

Parasite Tomato Hornworm

Tomato Hornworm with parasitic Braconid wasps.