Interaction Terminology

By TERRY GOUTHRO, DECEMBER 15, 1987 and extended by DAVID RICE, DECEMBER 14, 1990

Useful Definitions of Interaction

  1. Neutralism
  2. Synergism
  3. Mutualism
  4. Amensalism
  5. Commensalism
  6. Competition
  7. Predation
NEUTRALISM: represents a lack of of interaction between two populations. The significance of neutralism is difficult to evaluate. It can occur if populations are far apart. It would be found most frequently in very dilute populations where competition would be minimal or when the organisms use different substrates and need not compete.

Neutralism has been observed in a chemostat culture of Lactobacillus and Streptococcus yoghurt starter cultures. The individual population sizes in the chemostat were found to be the same as the separate mono-cultures under the same conditions.

SYNERGISM: Both organisms benefit from the relationship but the association is not obligatory.

MUTUALISM: Obligatory relationship between two populations that benefits both populations. In mutualism, the interaction is necessary for survival. Symbiosis describes specific interactions that cannot be performed alone, and like synergism, are not necessary for survival.

One case of mutualism is the action between L. arabinosus and S. faecalis which release phenylalanine and folic acid respectively.

There are numerous cases of symbiosis involving plant and animals and microbes, e.g., the interaction of insects with yeast.

AMENSALISM: Association which is detrimental to one species and neutral to the other.

In amensalism, the unaffected population releases agents such as antibiotics that restrict the the growth of the other population.

Amensalistic interactions can induce dormancy or morphogenesis in the antagonized population. One case with relevance to the milk fermentation process is the interaction between the nisin-producing S. lactis and the restricted L. casei.

Non-specific amensalism can result from the lowering of the system pH or the production of oxygen or hydrogen peroxide.

There is some overlap between amensalism and competition, although the latter must be a two-way process.

COMMENSALISM: Association in which one organism is benefitted and the other organism is neither benefitted nor harmed.

Commensalism is common and is a significant factor in organism succession within microbial communities. An example is S. cerevisiae releasing riboflavin for use by L. casei for growth.

Prior modification of the environment by one organism often leads to better growth for another organism. Examples of environmental changes include the removal of oxygen for anaerobic processes, raising the water content, reducing the osmotic pressure and detoxifying the environment. This process is called metabiosis and is used for the production of the Japanese drink sake.

COMPETITION: an interactive association between two species both of which need some limited environmental factor for growth and thus grow at suboptimal rates because they must share the growth limiting resource.

Competition is the single most important interaction in nature. Experiments have shown that some or all of the less competitive organisms are not eliminated, but stable coexistence can occur. Commensalism and mutualism among some of the organisms could be responsible for this, or it may result from a population that that preys on the competing organisms.

The competing populations can be stabilized by feedback control.

PREDATION: An interaction between organisms in which one benefits and one is harmed based on the ingestion of the smaller sized organism, the prey, by the larger organism, the predator.

Predation is brought about by endocytosis and is restricted to certain protozoa and others with amoebal phases. The end result is an oscillation between the predator and the prey.

James P. Bignell, B.S. Biology, M.Ed, ATM-S, objected to this definition and provided a better one:

PREDATION:    any relationship in which one organism captures, subdues, and feeds upon another organism.
Examples of this behavior are phagocytosis as in an amoeba capturing a bacterium or paramecium or an African Lion subduing a zebra.  Often the predator (the feeding species organism) is larger than the prey (the food organism) as in many microbial relationships.  There are many cases in which the prey is larger as when carnivores subdue herbivores.

Parasitism is when the predator is smaller than the prey. A wide range of microbial groups contain parasitic members: viruses, bacteria, and amoebae.

Indirect parasitism involves the the absence of cell contact during the process.

Another term, symbiosis, simply means coexistence or living together; it is not specific enough to deserve an entry in the table.

In complicated mixtures of organisms, individuals usually play several roles. For example, they can prey on others while being themselves the food for larger organisms.

Another contribution by James P. Bignell (I don't agree completely, but our two differing viewpoints should provoke some thought. H.B. ):
SYMBIOSIS:  any relationship in which two (and possibly more) individuals of differing species coexist and mutually benefit each other.
An example of this behavior is the relationships between in most lichen species between the fungus and the algae where the fungus provides protection from drying and the algae produces organic nutrients through the process of photosynthesis.  Another prominent example is the relationship between the termite which cannot digest the wood (cellulose) it consumes and the intestinal resident protist that can digest the cellulose.  The termite provides protection and food for the flagellated protist Trychonympha while the protist digests the cellulose so the termite can utilize the glucose produced for energy.
Mutualism is one form of symbiosis and the two terms are often used interchangeably.

  • Move to NEXT topic
    or jump ahead to:
  • Competition
  • Predation
  • Mutualism
  • Commensalism
  • Comments about ecosystems and some terminology
  • Computerized analysis of an ecosystem



    converted from BASIC exercise, Oct. 1996