3.7: Ecological Interactions- Two-Species Model
Two-species model allows to describe how two theoretical species might influence each other. For example, Species I may facilitate Species II: it means that if biomass (sum of weight) of Species I increases, biomass of Species II also increases ( \(+\) interaction). There are also \(+\) and \(0\) interactions. Two species and three signs make six combinations:
| + | 0 | - | |
| + | mutualism | commensalism 1 | exploitation 2 |
| 0 | ... | neutralism | amensalism |
| - | ... | ... | interference 3 |
\(^1\) Includes phoresy (transportation), inquilinism (housing) and “sponging”.
\(^2\) Includes predation, parasitism and phytophagy.
\(^3\) Includes competition, allelopathy and aggression.
- Mutualism
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It sometimes called “symbiosis”. Two different species collaborate to make each other life better. One of the most striking example is lichenes which is algae-fungus mutualism.
- Commensalism
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Remember “Finding Nemo”? Clown fish lives inside actinia. This type of commensalism is called “ housing ”. Another example is suckerfish and shark, this is phoresy . Sponging happens when scavengers feed on what is left after the bigger carnivore meal.
- Exploitation
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This is the most severe interaction. Predation kills, but parasitism or phytophagy (the only difference is that second uses plants) do not.
- Neutralism
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Rare. Philosophically, everything is connected in nature, and if Species I and II live together, they usually interact, somehow.
- Amensalism
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This happens when suppressing organism is, for example, much bigger then the “partner”. Big trees often suppress all surrounding smaller plants.
- Interference
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Competition happens when Species I and II share same ecological niche, have similar requirements. Gause’s Principle says that sooner or later, one of them wins and another looses. Allelopathy is a mediated competition, typically through some chemicals like antibiotics. Most advanced (but least pleasant) is the direct aggression when individuals of one species physically eliminate the other one.