Ecological Niche: Hypervolume model

Niche is the idea of a profession for organisms in its ecosystem. It is a concept that describes the function that an organism carries out in the ecosystem. But this function is defined by many parameters prevent within the ecosystem. Depending on these parameters, the niche of an organism can vary in spatial and temporal extent; from ecosystem to ecosystem. One model which accounts for the environmental factors influencing an organism’s niche is the hypervolume model.

How do environmental factors affect niches?

An organism survives in a place because of the environmental factors present there. An elephant lives in the African Savannah because the area has grasses (the elephant’s diet), open spaces (elephants can’t live in confined burrows, can they?), hot and humid climate, etc. It is environmental factors that any organism is adapted for. Therefore, it is logical to consider that if the environmental factors affect the living space, they will affect the role the organism plays.

Let’s look at the African Elephant example some more. The role it plays in the Savannah ecosystem is immense. For instance, because it is so hot there, there is hardly any surface water. Elephants dig up water holes to extract groundwater onto the surface. This allows other organisms to use the water after the elephants leave. Therefore, the temperature and water availability (or the lack of it), forces the elephant to come up with a way to counter it. As a consequence, it plays the ecological function of providing a water resource to other land animals of the Savannah.

The hypervolume niche

Going by this, we can theoretically depict the function that an organism carries out by plotting a graph with the environmental factors that will govern that function. For example, in the above example, the two environmental conditions are temperature and water availability. Putting one on each axis of a graph, we determine the extent of each factor within which an elephant will occur. The space generated (in this case, an area) from this will represent the ecological niche of the elephant.

niche

This model was given by G.E. Hutchinson of Yale University in 1965. The concept is called “hypervolume” because it is not just two factors that controls the niche of an organism. If we were to take 3 factors; temperature, water and population size (more elephants can dig out more area and create a larger water hole), the the resulting space from the graph will be a volume.

Extending this, if there are number of environmental factors (both biotic and abiotic), the resulting space will be a hypervolume; not something that can be perceived by the human mind. This space is called the hypervolume niche.

Application in ecological studies

This concept has a very interesting application in ecological studies, particularly in studying the competition between two populations of organisms. When the hypervolume niche for an organism is generated independent of other organisms, it is called fundamental niche. However, it is very rare for an organism to occupy it’s fundamental niche in nature. That is because there are many other animals competing for the same resources (ie. they are governed by similar environmental factors). For example, zebras and hyenas in the Savannah both would like to drink water from the same water hole created by the elephant. “Water” here, becomes the common factor.

When such common environmental factors are present, the hypervolume niches of the two organisms will intersect in space. This results in competition between the two organisms.

If the overlap is not to a large extent, then the two organisms may be able to coexist. For example, the zebras and hyenas would come to use the water hole at different times of the day, or they would access the water hole from different directions. Therefore, they are not utilizing their entire niche (which here would mean, the entire water hole). They have a smaller section of the niche. This is common in nature, and is called realized niche.

However, if the overlap is complete or to a large extent, ie. if the two organisms have strikingly similar environmental factors governing them (same food, same water resource, same shelter requirements), then it leads to intense competition. They cannot coexist. Eventually, the fitter organism will drive the other to extinction.

Hypervolume is not restricted to ecology or niches. These simulations also help us study processes like migration.The pictures below depict one such study, where hypervolumes where used to describe population migration to and fro an archipelago. They have also been used in other disciplines like physics, economics etc.

../_images/hv_best_fair_migration_policy.png hypervolume के लिए चित्र परिणाम

Hypervolume niche cannot be understood completely, ever.

While it is seen in nature, humans cannot percieve it’s extent. Therefore, in all our niche studies, we are forced to consider a maximum of three environmental factors at a time. This is the biggest limitation to it’s application. Maybe someday, humans will evolve into perceiving more than three dimensions; that would be a very interesting day for me. I would love to see nature in all it’s layered, complex glory.

 

 

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