Competition and coexistence in ecology: What happens when new species enter an ecosystem

We’ve seen what happens when species is lost from an ecosystem. Actually, we are continuing to see this happening in pretty much every ecosystem on the planet. Loss of biodiversity is not an issue that is alien to us (certainly not alien to the readers of this blog). I’ve gone into this in greater detail in Earth’s Paradox: Greater complexity, more stability, which you can take a look at.

But what happens when new species enter an ecosystem? Do they coexist with the existing species or do they find a way to survive by killing native species?

What determines whether species compete or coexist?

The introduction of new species in an ecosystem can have multiple effects. This depends on two factors: interspecific and intraspecific competition.

Interspecific vs intraspecific competition

Interspecific competition is between the two different species present in the ecosystem. For example, if humans invaded a forest and established agricultural land, the competition for resources between elephants and humans will be interspecific. This is also called contest.

Intraspecific competition is the competition between individuals of the same species. In our previous example, the competition for resources among different families in the human settlement will be intraspecific (the competition between individual elephants is also intraspecific). This is called scramble.

Depending on the how the interspecific and intraspecific competition plays out in an ecosystem, three conditions will arise.

When Interspecific > Intraspecific: Competitive Exclusion Principle

In this condition, there is greater competition between the two species than within the species.

From the our example between elephants and humans, the elephants and humans are competing with each other rather than among themselves for resources (interestingly, the entire plot for Planet of the Apes is based on this phenomenon).

In such situations, one of the species is completely removed and the other survives. This is called the competitive exclusion principle. Generally, the species that started out with a greater population tends to survive such competition.


When Interspecific < Intraspecific: Coexistence

Here, the humans are too busy fighting for land among themselves to worry about elephants, and the elephants seem to be doing the same thing.

An interesting outcome arises because of this. Due to such high competition within a species, neither species is able to attain maximum population density in the ecosystem.

Their need for resources, therefore, which be much less. They involuntarily partition their resources. This will allow both species to coexist.


When Interspecific ~ Intraspecific: Competitive exclusion and survival of the fittest

In this situation, there is an equal level of competition between species and within species.

So, the humans continue to fight for larger chucks of land and resources, but also recognize the presence of elephants in the area. They also do not want the elephants to have the resources.

This is the most common situation that is found in real life ecosystems, especially when humans are one of the interacting species. What do you think this results in?


It results in the complete obliteration of one species, while the other triumphs. The one that triumphs and survives is the fitter species of the two. In human-animal interactions, obviously it is the humans who come out on top.

Why is it important to study competition and coexistence in nature?

Humans have caused insertion of many species in ecosystems around the world. Often, they are themselves the invasive species. Understanding the competition dynamics helps us mitigate them better.

Wherever humans are involved, the competition generally results in long-term human-wildlife conflicts. Understanding competition dynamics helps us manage and conserve animal populations by deciding on the right mitigation measures.

Competition and the survival of the fittest organism is the reason we see the organisms around us. However, today the competition has arisen due to a lot of artificial influences, that is not only reducing species diversity but also decreasing heterogeneity in the ecosystems. This is a major cause of concern; therefore it should be studied and mitigated.

Author: Saurab Babu

Usually found sitting with a good book, nibbling on a piece of dark chocolate. Always ready for a good story.

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