Community Interactions: Mutualism (+/+) & Commensalism (+/0) - Online Tutor, Practice Problems & Exam Prep

Community interactions include competition, exploitation, mutualism, and commensalism. Competition is a minus minus interaction, negatively affecting all involved. Exploitation, a plus minus interaction, benefits one organism while harming another, encompassing predation, herbivory, and parasitism. Mutualism is a plus plus interaction where both organisms benefit, sometimes obligately. Commensalism, a plus zero interaction, benefits one organism while the other remains unaffected. Both mutualism and commensalism fall under symbiosis, highlighting the complexity of ecological relationships.

Positive Interactions

In this video, we're going to talk about the 3rd and the 4th community interactions in our lesson, which are often grouped together as positive community interactions, and these are mutualism and commensalism. Now, mutualism is a community interaction where both organisms benefit from the interaction. So mutualism is a plus plus interaction. Although this is not always the case, sometimes the 2 mutualistic organisms may actually depend on each other for their long-term survival. And we call this type of mutualism obligate mutualism since the mutualistic relationship is obligatory for those organisms.

Now down below, we're showing you just an example of mutualism between this red-billed oxpecker, this bird, and this impala here. And so the red-billed oxpecker is eating ticks in the impala's fur. And so the red-billed oxpecker is getting a food source from the impala. So that's a positive benefit for the red-billed oxpecker. Now the impala, on the other hand, is getting its fur cleaned by the red-billed oxpecker as the parasites are being removed.

And so that's a positive benefit for the impala. And so because this is a plus plus interaction, again, this is what makes this mutualism. Now on the other hand, commensalism is a community interaction where only one organism benefits and the other organism is not affected. And so commensalism is a plus zero interaction. And so as an example, let's take a look at this shark here, which is closely interacting with these smaller fish called remora, which follow the shark around.

And so these remoras are going to be eating scraps of food that are left behind by the shark. And so the remoras, by interacting with the shark, are benefiting because they get a food source. Now the shark, on the other hand, gets no tangible benefit or drawback from their interaction with the remoras. And so it is neutrally affected and we indicate that with the number 0. Now the very last thing that I'll leave you all off with here is that mutualism and commensalism both fall under the category of symbiosis, which is a term that refers to any close and prolonged interaction between two species.

And so once again, mutualism and commensalism are both falling under the category of symbiosis. But parasitism, which we recall is a different type of community interaction called exploitation, is also falling under the category of symbiosis as well. So this here concludes our lesson on these positive community interactions, and I'll see you all in our next video.

Certain strains of E. coli bacteria can live in human intestines, where it relies on intestinal contents for nutrition. This bacterium also produces vitamin K, which humans use to produce blood clotting factors. In this case, the relationship between humans and E. coli is:

• A. Mutualism.
• B. Commensalism.
• C. Parasitism.
• D. Exploitation.

You observe an interaction between two species. Removal of species A has a negative impact on species B. Removal of species B has a positive impact on species A. Which of the following is the most likely relationship between the two organisms?

• A. They have a mutualistic relationship.
• B. Their interaction is commensalism, as species B no longer benefits when species A is removed.
• C. They are competitors with a similar niche.
• D. Species B is a parasite that relies on species A.

Summary of Community Interactions

This video, we're going to briefly summarize the 4 types of community interactions, their effect on fitness, and cover some important notes. The first type of community interaction that we covered in our lesson was competition. Competition is a minus minus interaction where the fitness of all competing organisms is negatively affected. Recall that competition can lead to either competitive exclusion and local extinction of the weaker competitor when there's complete niche overlap between the competing species, or competition could lead to resource partitioning and character displacement when there's only partial niche overlap between the competing species.

The next type of community interaction that we covered in our lesson was exploitation, which is a plus minus interaction, meaning that one organism is benefiting at the cost of another organism being harmed. Recall that there are 3 main types of exploitation, which are predation, herbivory, and parasitism. The next type of exploitation that we covered in our lesson was mutualism, which is a plus plus interaction where both organisms benefit from the interaction. Mutualism is common in nature and some species may actually depend on each other for survival, and we call this obligate mutualism.

Last but not least, commensalism is a plus zero interaction, where one organism benefits and the other organism is neutrally affected, meaning that it is not affected. Commensalism often involves using another organism or its byproducts as shelter, food, transportation, or habitat.

This here concludes our summary and I'll see you all in our next video.