The Relationship Between Rats And Humans: Parasitism, Mutualism, or Commensalism

Alyssa Pustilnik

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Our inspiration:

Lorem Ipsum

Rats by Robert Sullivan

We decided to do a research project on rats because we are currently reading a very interesting book on rats and their interactions with humans. At the same time in science we were learning about the different symbiotic relationships between different organisms. The idea we came up with combines both classes and we are both genuinely interested in this topic. We are trying to make a decision if the relationship between rats and humans is parasitism, mutualism, or commensalism.


Background information

It is evident that rats have some sort of symbiotic relationship with humans because humans and rats have been coexisting ever since the introduction of rats to areas where humans live.

  • The rats we will be discussing today for mutualism are the Rattus norvegicus also known as the brown rats. These rats are common all over The United States and the only species of rats in New york. Long ago there used to be a species of rats called the Rattus rattus also knows as the black rat but they were driven away by the brown rats. Now the only area in America where black rats coexist with brown rats is California.
  • The rats we will be discussing today for parasitism are just general rats located all over the world and may have the ability to harm humans. An example would be during the Bubonic Plague.The Plague is an infectious disease caused by bacteria called Yersinia pestis. These bacteria are found mainly in rodents, particularly rats, and in the fleas that feed on them.

How to tell the difference betweeen two common rats: Rattus rattus and Rattus nervegicus

The symbiotic relationship may be Commensalism

Commensalism involves interactions where populations interact so that only one population benefits from the interaction while the other neither benefits nor is hurt by the interaction.

  • The fact that humans offer shelter to other rats is one example. While there are many other sub-interactions that spawn from this interaction, by itself this is commensalism.
  • Rats living in or near landfills are also an example of commensalism because in a landfill they typically do not live long enough to build a population size large enough to help human, and since it is only a landfill they do not have the opportunity to hurt humans significantly. They only are able to feed off of the trash for a period of time.

The symbiotic relationship may be Mutualism

Mutualism is a relationship between populations where both populations gain something from the interaction. Most New Yorkers might find it harder to describe smaller interactions that we have with rats that would fit into this category but as it turns out, in exchange for the food and shelter we provide rats, there are some valuable services they offer in return. These interactions include:

  • Serving as detritivores. Not only do rats eat out of trash cans, but they also serve to reduce litter placed in places that might not always be attended to immediately and even clean up trash produced by other animals like the remains of dead birds. In addition to providing the service of actually removing the trash, the presence of rats mean that the refuse is not as able to harbor bacteria which can prove even more harmful to humans, or cockroaches. Rats also continue to service as detritivores through the winter when insects are less active.
  • Proving subjects for labs to experiment on and for humans to keep as pets. Most lab rats and rats kept as pets were selectively bred from the same brown rat that roams the streets of New York City but now sacrifice themselves for the sake of scientific advancements and providing companionship to humans.
  • Keeping populations of urban predators in check. The population of the Red Tail Hawk in New York City has been raising over the course of the past few years despite continued development, which has been attributed to the rising rat population. The correlation was so strong and so important to New Yorkers that the city now reduces its effort to poison rats during breeding season for the hawks in order to protect their numbers.

The symbiotic relationship may be Parasitism

Parasitism is an interaction between populations where one population benefits and the expense of the other. Some of the interactions between humans and rats that fall into this category are:

  • The need for rats to chew on objects to keep the size of their teeth manageable. It is estimated that the teeth of rats can grow between 4.5 inches and 5.5 inches in a year. In order to keep their incisors at a healthy length, the rats are forced to chew on things like wires and bricks.This is mostly harmful to humans, and only benefits the rats.
  • The tendency for rats to eat out of the trash cans of humans and out of kitchens. These instances of the rats appetite offer no significant benefit to humans but instead only creates a mess and can even spread disease.

We think the symbiotic relationship is ..............


What symbiotic relationship do you think it is?