Ecological relationship status

This exercise is a part of Educator Guide: Where Bacteria Live On Our Tongues / View Guide

Directions for teachers:

Ask your students to read the online Science News article “Here’s where bacteria live on your tongue cells” and answer the individual questions, which ask them to define and give examples of ecological relationships. Have students partner up to discuss the last prompt, which asks them to describe relationships in their community as interspecific interactions, and create metaphors based on those descriptions. Bring the class back together as a group and have each set of partners share one of their metaphors.

Want to make it a virtual lesson? Post the online Science News article “Here’s where bacteria live on your tongue cells” to your virtual classroom and ask students to read the article and answer the individual questions. Pair up students to discuss and answer the partner prompt using a video conferencing platform, or talking by phone. They can collaborate in a shared document during the conversation. Post the partner discussion prompt to an online discussion board. Have students give feedback about another partnership’s response.

Individual Questions

1. What organisms make up the ecological community identified in the article? Describe the community’s environment.  

Humans and the different types of bacteria that live on human tongue cells, including Actinomyces, Rothia and Streptococcus, make up the ecological community. A human tongue is a warm and moist environment. The tongue moves a lot and often is exposed to air and food that humans eat.    

2. What are the general interactions among the organisms in the ecological community?

Bacteria interact with their human host as well as with each other.

3. Relationships between different species shape how ecological communities form. Scientists define the relationships, called interspecific interactions, by the beneficial, harmful or nonexistent effects the interactions have on species. Do your own research to define and give an example of each type of interspecific interaction listed below. Indicate the effect of the interaction on both species. Be sure to use reliable sources.


Competition is an interaction in which two species use the same limited resource, such as food or building materials. Competition generally has a negative or harmful effect on the involved species. For example, green anole lizards in Florida compete for habitat and food with brown anole lizards — an invasive species introduced from Cuba and the Bahamas. Over time, one species may outcompete the other for resources, leading to population declines and even local extinction of the weaker species.      


Predation is an interaction in which one species uses another species as a resource. Predator species benefit from this interaction, while prey species are harmed by it. An example is African lions that kill and eat gazelles. A special case of predation is herbivory, in which a plant is the prey species.   


Commensalism is an interaction that benefits one species and has no effect on the other species. An example is remora fish, which harmlessly attach themselves to sharks and other fishes and feed on scraps left over from the hosts’ meals.


Mutualism is an interaction that benefits both species by increasing their chance of survival or reproduction. An example is the relationship between red-billed oxpeckers and black rhinos. The birds feed on ticks and other parasites on the rhinos’ hides. In return, the oxpeckers appear to warn the mostly blind rhinos of nearby potential threats, such as people. (See the Science News article “Hitchhiking oxpeckers warn engendered rhinos when people are nearby.”)


Parasitism is an interaction in which one species depends on the other species for survival. The interaction benefits the parasite species and harms the host species. An example is tapeworms that live in the intestines of animals. Tapeworms absorb some nutrients as food is digested, depriving the animals of those nutrients.

4. What interspecific interactions exist between the organisms in the article? Explain the effects the interactions have on each organism.

Bacteria interacting with their human host could be an example of mutualism. The interaction would benefit both the human host and some of the bacteria — the tongue provides a habitat and nutrients for Actinomyces and Rothia bacteria, and the bacteria may convert dietary nitrate to nitric oxide that helps regulate blood pressure.

The interactions between different types of bacteria may be an example of mutualism. Some bacteria might work together to create a healthy environment in which they all can thrive.

5. What other examples of interspecific interactions do you think might exist in the community?

Bacteria likely compete for resources on the tongue. Some types of bacteria may also have commensal relationships with each other or with the human body. For example, the bacteria might benefit from inhabiting the tongue, but have no effect on the human.

6. Why do you think the different types of bacteria found on tongue cells are organized into “neighborhoods”?

The patterns found within the bacterial community on tongue cells are likely due to the resources available in the environment, as well as the interspecific interactions that exist among the different types of bacteria.

Partner Discussion With a partner, think about a community you are familiar with, such as your school, your neighborhood or your town. Identify relationships among people in your community. Next, choose three types of interspecific interactions and explain how some of the community relationships you identified may be similar to those interactions. Finally, create metaphors based on your explanations.