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.
Mutalism
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
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.
Commensalism Examples
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
Parasitism is a type of relationship where one organism benefits and the other organism is harmed in some way.
Parasitism Examples
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.
Review
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
The answer is C.
Crows and other birds will get a free meal by eating insects and fleas off of the backs of cattle and cattle will get a free cleaning. Both the crows and the cattle benefit, so that makes this relationship mutual.
Thanks for watching, and happy studying!
Commensalism is a type of relationship between two living organisms in which one organism benefits from the other without harming it. A commensal species benefits from another species by obtaining locomotion, shelter, food, or support from the host species, which (for the most part) neither benefits nor is harmed. Commensalism ranges from brief interactions between species to life-long symbiosis.
- Commensalism is a type of symbiotic relationship in which one species benefits, while the other species is neither harmed nor helped.
- The species that gains the benefit is called the commensal. The other species is termed the host species.
- An example is a golden jackal (the commensal) following a tiger (the host) to feed on leftovers from its kills.
The term was coined in 1876 by Belgian paleontologist and zoologist Pierre-Joseph van Beneden, along with the term mutualism. Beneden initially applied the word to describe the activity of carcass-eating animals that followed predators to eat their waste food. The word commensalism comes from the Latin word commensalis, which means "sharing a table." Commensalism is most often discussed in the fields of ecology and biology, although the term extends to other sciences.
Commensalism is often confused with related words:
Mutualism - Mutualism is a relationship in which two organisms benefit from each other.
Amensalism - A relationship in which one organism is harmed while the other is not affected.
Parasitism - A relationship in which one organism benefits and the other is harmed.
There's often debate about whether a particular relationship is an example of commensalism or another type of interaction. For example, some scientists consider the relationship between people and gut bacteria to be an example of commensalism, while others believe it is mutualistic because humans may gain a benefit from the relationship.
- Remora fish have a disk on their heads that makes them able to attach to larger animals, such as sharks, mantas, and whales. When the larger animal feeds, the remora detaches itself to eat the extra food.
- Nurse plants are larger plants that offer protection to seedlings from the weather and herbivores, giving them an opportunity to grow.
- Tree frogs use plants as protection.
- Golden jackals, once they have been expelled from a pack, will trail a tiger to feed on the remains of its kills.
- Goby fish live on other sea animals, changing color to blend in with the host, thus gaining protection from predators.
- Cattle egrets eat the insects stirred up by cattle when they are grazing. The cattle are unaffected, while the birds gain food.
- The burdock plant produces spiny seeds that cling to the fur of animals or clothing of humans. The plants rely on this method of seed dispersal for reproduction, while the animals are unaffected.
Inquilinism - In inquilinism, one organism uses another for permanent housing. An example is a bird that lives in a tree hole. Sometimes epiphytic plants growing on trees are considered iniquilism, while others might consider this to be a parasitic relationship because the epiphyte might weaken the tree or take nutrients that would otherwise go to the host.
Metabiosis - Metabiosis is a commensalistic relationship in which one organism forms a habitat for another. An example is a hermit crab, which uses a shell from a dead gastropod for protection. Another example would be maggots living on a dead organism.
Phoresy - In phoresy, one animal attaches to another for transport. This type of commensalism is most often seen in arthropods, such as mites living on insects. Other examples include anemone attachment to hermit crab shells, pseudoscorpions living on mammals, and millipedes traveling on birds. Phoresy may be either obligate or facultative.
Microbiota - Microbiota are commensal organisms that form communities within a host organism. An example is the bacterial flora found on human skin. Scientists disagree on whether microbiota is truly a type of commensalism. In the case of skin flora, for example, there is evidence the bacteria confer some protection on the host (which would be mutualism).
Domestic dogs, cats, and other animals appear to have started out with commensal relationships with humans. In the case of the dog, DNA evidence indicates dogs associated themselves with people before humans switched from hunting-gathering to agriculture. It's believed the ancestors of dogs followed hunters to eat remains of carcasses. Over time, the relationship became mutualistic, where humans also benefited from the relationship, gaining defense from other predators and assistance tracking and killing prey. As the relationship changed, so did the characteristics of dogs.