Mutualism, Commensalism, and Parasitism
Hi, and welcome to this video on mutualism, commensalism, and parasitism!
Have you ever noticed any interactions between organisms in nature that you thought were especially interesting? Like bees pollinating flowers or clownfish living in sea anemones? Symbiotic relationships like these are all around you if you know where to look. Organisms can use such a relationship to benefit from one another in several ways, such as transportation, food, shelter, growth, and reproduction, just to name a few.
So if we take the two examples we just mentioned, the bees pollinating the flowers and the clownfish living in sea anemones, we have two classic examples of how organisms can mutually benefit from one another so that both organisms can thrive. When both organisms in a symbiotic relationship benefit, we call this mutualism. In the case of the bees and the flowers, bees need pollen to make honey which they use as a food source, so the bees go from flower to flower gathering pollen which they store in a pouch in their abdomen or on their hind legs depending on the species. When the bees move on from one flower to the next, some of the pollen brushes off and pollinates the new flower. Both the bees and the flowers benefit from this relationship, so it’s a good example of mutualism. Clownfish and sea anemones have the same sort of mutualistic relationship. To other fish, brushing up against a sea anemone is deadly. But clownfish are unaffected by the anemone’s sting because they have adapted to form a protective mucous on their skin. So the clownfish is able to live in the sea anemone and in the process keeps it clean, while the sea anemone gives the clownfish protection and a place to live.
Another example of mutualism that you may not have thought of is the symbiotic relationship between, us, humans, and the bacteria in our gut. Take lactobacillus bacteria for a specific example. Lactobacilli are a common type of bacteria found in yogurt, cheese, and some plants. So when you eat any of these foods, the bacteria will make a home out of your intestines by feeding off of the sugars you eat while simultaneously helping you digest that sugar. Both parties benefit, so this is also a mutualistic relationship.
Commensalism is another type of symbiotic relationship where one organism benefits and the other organism isn’t benefited or harmed either way. Golden jackals will follow tigers on their hunt for prey so that they can feed off of the tiger’s scraps. The tiger does all of the work to actually catch and kill its prey, but it doesn’t seem to mind the jackal cleaning up after it. Since the jackal benefits and the tiger isn’t affected, we can say that this is an example of commensalism.
Another example of commensalism is one organism using another as a means of transportation. A lot of insects, fish, and other animals use each other in this way, but a good example is the remora. This is a type of suckerfish that will attach itself to sharks and other big fish to catch an underwater ride. This in and of itself is an example of commensalism since only the remora really benefits, but this relationship can change to mutualism when the remora feed on the parasites on the backs of these big fish. This leads us to our last type of relationship, which is parasitism.
Parasitism is a type of relationship where one organism benefits and the other organism is harmed in some way.
Your mind might jump to what we more commonly think of as a parasite like tapeworms or fleas. These are great examples because in both cases, the parasite benefits while the other organism is harmed. As humans, we can get tapeworms from the food and water we consume if it is not treated or prepared properly. Once the tapeworm is inside of the digestive tract, it eats a lot of your food for you. So symptoms can range from increased appetite to nausea, but if the tapeworm spreads to other organs it can be life-threatening. However, parasitic relationships aren’t limited to the microscopic or small-scale world. Cowbirds are a species of birds that instead of raising their own young, take advantage of another bird species, since birds cannot easily distinguish between their young. Female cowbirds will lay their eggs in another bird’s nest, like a black-capped chickadee, and the female black-capped chickadee will feed both her own young and the cowbird nestling. However, cowbirds are much larger than most birds so they will demand more of the food and nest space. In the end, this means some of the black-capped chickadee’s young will die while the cowbird nestling lives.
So, to review, mutualism is where both organisms benefit, commensalism is where one benefits and the other is unaffected, and parasitism is where one benefits and the other is harmed.
Before we go, here’s a review question:
Which is the best example of mutualism?
- A flea and a dog
- A squid and an anglerfish
- Cattle and crows
- A poison dart frog and a cricket
Thanks for watching, and happy studying!