Mutualism: An ecological process of interdependence, crucial for survival  

Do you know what a food chain is? It is the feeding relationship between species in a biotic community. For instance, a grasshopper eats a plant, a mouse in turn eats the grasshopper. Following this, a snake eats the mouse, then an eagle eats the snake. Finally, when the eagle dies, fungi decompose its body and turn it into nutrients that are derived by the plant. This is a complete food chain. So, it is a vicious cycle, where all the creatures are dependent on one another. If one is taken out, the food web becomes incomplete and invalid.  

Well, just like a food chain, there are other scientific phenomena existing in an ecosystem. One such is mutualism. Here, it refers to an interaction between two different species that in the long run benefits both (in a positive way) and typically involves exchange of substances or services. In fact, it affects the entire survival, starting with reproduction to defence to feeding relationships and can be acknowledged as vital to the patterns and processes that occur within ecological systems.  

Mutualism throughout history 
The definition and understanding of mutualism can be traced back to many centuries, since the time of Aristotle. However, it was in 1876 that the term “mutualism” emerged in the hands of Belgian scientist Pierre-Joseph van Beneden who in his book Les Commensaux et Les Parasites stated that there is mutual help among many species with services being rewarded with good behaviours or in kind and vice versa. Later, it was Charles Darwin who picked up from where Beneden left off and explained mutualism with respect to pollination. He demonstrated how plants and animals are both involved in the process and also benefit from it. Fast forward to the mid-1930s and mutualism started being deemed as a concept that affects all kinds of ecological processes and in turn the growth of species.  

Types of mutualism 
Mutualism, as you may have understood by now, is a wide concept, which is why scientists divide it into five categories. Let us look at them closely. 

Obligate mutualism: This refers to a mutualistic connection that has developed to the point where two species are totally dependent on one another. For example: fungus and farming ants where none can live without the other. This in turn helps in co-evolution. 

Facultative mutualism: Here, the two species can co-exist without relying on each other but are still involved in an indirect relationship. For example, honeybees and humans, where the former produce the honey, and the latter consumes it. But they can survive without one another. 

Trophic mutualism: This is where the two species figure out complementary ways to derive nutrients and energy from each other. For instance, cows and bacteria. Cows feed on plants that are high in cellulose but are naturally unable to digest it. This is when bacteria assist in digestion of the cellulose. In return, the cow lets the bacteria survive inside it and even provides food and warm environment to sustain it.  

Dispersive mutualism: This kind of mutualism specifically involves species that assist in the movement of pollen grains from one flower to another in exchange for nectar. In other words, they help in dispersal of seeds in return for the nourishing fruits that contain the seeds.  

Defensive mutualism: As the name suggests, here one species obtains food or shelter or other necessities in exchange for defence help such as against potential predators. Example: Shrimp in marine ecosystem helps clean parasites from catfishes and in turn seek help when they are attacked by larger fish.  

Humans and mutualism 
Apart from honeybees, humans share a wide range of mutualistic relationships with different species. For instance, there’s a fungus called gut flora that helps people in digestion and can only survive inside human bodies. Similarly, head lice, although seems yucky, help humans to stimulate immune response from far lethal parasites and in turn gain some nutrients from human hair. However, the best example is of course how humans use oxygen produced by plants and exhale carbon dioxide that plants use to survive.