Often times relations that are established between animals in nature are classified according to the convenience that represents each of those who perform it: while there are some relationships that are of mutual dependence and then both species find it useful, others such as predation have a predator and a prey, where only the former is benefited.
Relationships in which at least one of the species is harmed are called negative interactions: it is the instinct of the species and the dynamics of evolution itself that determines that these relationships take place, and not a tangible will because if it were so, no species would cause damage.
It is called amensalism to those relationships between species in which one of the two is harmed by the relationship and the other does not experience any alteration, that is, it is neutral. For example: when some animals trample the grasses, without taking advantage of them for a particular use.
How is amensalism carried out?
Usually, amensalism occurs in the generation of toxic substances, or in the creation of intolerable conditions for other populations, by microorganisms.
When an organism establishes itself in a space, it often does what is necessary to prevent other populations from surviving in it, which cannot be interpreted as a positive action for itself: rather it is thought of as neutral to itself, but harmful to the rest of the species.
Difference between amensalism and competition
Amensalism is often confused with another relationship that can occur between species, which is that of competence: that is the one that contains a fight between two organisms to obtain the same resources, which they use to satisfy their needs.
While competition is a game ‘zero sum’ whereby the convenience of one necessarily implies the detriment of the other, in amensalism whoever performs the delimiting action does not gain a real advantage.
Examples of amensalism
- When some animals trample the herbs, without taking advantage of them for a particular use.
- The penicium fungus, which secretes penicillin preventing the growth of bacteria; and not only bacteria that can affect it.
- Some planktonic algae release a toxic substance, which is concentrated in the ‘red spots’ of the ocean, causing the death of various species of marine animals.
- A wasp that lays its eggs in aphids, being that when the larvae are born they feed on them.
- A rodent that feeds on the fruit of the carob tree, but that does not damage or modify the seeds during its digestion: since they come out the same, the relationship causes them to disperse.
- Larger trees that prevent sunlight from reaching the grasses that are at ground level.
- Pine leaves that fall to the ground release a chemical that reduces the incidence of seed germination instead.
- Eucalyptus, which secretes a substance that prevents and hinders the development of other plants.