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Ecology
Types of ecological
interactions
M. Saadatian
www.soran.edu.iq
1
Types of ecological interactions
competition
predation
parasitism
Mutualism
Amenalism
commensalism
symbiosis
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Competition – two species share a requirement for a
limited resource  reduces fitness of one or both species
Competition is an antagonistic interaction between individuals, groups,
animals, etc. for territory or resources. It arises whenever two or more
parties strive for a goal which they do not want to share. Competition
occurs naturally between living organisms which co-exist in the same
environment.
Example: competition for light, for nutrients for water
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Amensalism
Amensalism is an interaction in which one organism is harmed, while the other is
unaffected, and not benefited. Most frequently this occurs when one organism exudes a
chemical compound that is detrimental to another organism.
Plant roots exude many compounds that either attract or repel bacteria, fungi or the roots
of other plants
allelo compounds = allelo pathogens Allelopathy
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Chemical competition (Allelopathy)
Allelopathy is a biological phenomenon by which an organism produces one
or more biochemical that influence the growth, survival, and reproduction of
other organisms. These biochemicals are known as allelochemicals and can
have beneficial (positive allelopathy) or detrimental (negative allelopathy)
effects on the target organisms. Allelochemicals are a subset of secondary
metabolism.
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Predation – one species feeds on another  enhances
fitness of predator but reduces fitness of prey
Predation describes an interaction where a predator feeds on an
organism that is attacked. The act of predation must result in the death
of its prey and the eventual absorption of the prey's tissue through
consumption. Other categories of consumption are herbivory (eating
parts of plants), which is not considered predation.
Clear examples of predation are insectivorous plants. But there are other plants
that kill plants by stealing their light.
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herbivory is a form of
predation
Symbiosis – two species live together  can include
parasitism, mutualism, and commensalism
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Parasitism – one species feeds on another  enhances
fitness of parasite but reduces fitness of host
A parasitic plant is one that derives some or all of its sustenance from another plant.
Parasitic plants have a modified root (haustorium) that penetrates the host plant and
connects to the xylem, phloem, or both. Animal parasites are generally much smaller than
their host; both are special cases of consumer-resource interaction. This does not apply
to plant parasites.
The Greater Dodder or the European dodder
(Cuscuta europaea) is a parasitic plant which
belongs to the family Convolvulaceae. It grows
on Asteraceae, Fabaceae, Chenopodiaceae, and
other herbaceous plants
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Mutualism – two species provide resources or services to each other  enhances
fitness of both species
Neutralism is where two species have no interaction at all;
a pink dolphin and a canopy lizard could be an example of neutralism.
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Commensalism – one species receives a benefit from
another species  enhances fitness of one species; no
effect on fitness of the other species
Commensalism benefits one organism while the other
organism is neither benefited nor harmed. It occurs when one
organism takes benefits by interacting with another organism
by which the host organism is not affected.
Example: mosses, ferns, orchids
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