Biological Interaction
Biological interactions are the effects that the organisms in a community have on one another. In
the natural world no organism exists in absolute isolation, and thus every organism must interact
with the environment and other organisms. An organism's interactions with its environment are
fundamental to the survival of that organism and the functioning of the ecosystem as a whole.[1]
The black walnut secretes a chemical from its roots that harms neighboring plants, an example ofantagonism.
The mutualism interaction between the red-billed oxpecker and the giraffe.
In Ecology, biological interactions can involve individuals of the same species (intraspecific
interactions) or individuals of different species (interspecific interactions). These can be further
classified by either the mechanism of the interaction or the strength, duration and direction of their
effects.[3] Species may interact once in a generation (e.g. pollination) or live completely within
another (e.g.endosymbiosis). Effects range from consumption of another individual
(predation, herbivory, or cannibalism), to mutual benefit (mutualism). Interactions need not be direct;
individuals may affect each other indirectly through intermediaries such as shared resources or
common enemies.
Competition
Competition is a mutually detrimental interaction between individuals, populations or species, but
rarely between clades.
Amensalism
Amensalism is an interaction where an organism inflicts harm to another organism without any costs
or benefits received by itself.[5] A clear case of amensalism is where sheep or cattle trample grass.
Whilst the presence of the grass causes negligible detrimental effects to the animal's hoof, the grass
suffers from being crushed. Amensalism is often used to describe strongly asymmetrical competitive
interactions, such as has been observed between the Spanish ibex and weevils of the
genus Timarcha which feed upon the same type of shrub. Whilst the presence of the weevil has
almost no influence on food availability, the presence of ibex has an enormous detrimental effect on
weevil numbers, as they consume significant quantities of plant matter and incidentally ingest the
weevils upon it.
Parasitism
This is not a bee, but a syrphid fly, a Batesian mimic.
In antagonistic interactions, one species benefits at the expense of another. Predation is an
interaction between organisms in which one organism captures biomass from another. It is often
used as a synonym for carnivory but in its widest definition includes all forms of one organism eating
another, regardless of trophic level (e.g., herbivory), closeness of association
(e.g., parasitism and parasitoidism) and harm done to prey (e.g., grazing). Intraguild
predation occurs when an organism preys upon another of different species but at the same trophic
level (e.g., coyotes kill and ingest gray foxes in southern California). Batesian mimicry is also an
antagonistic interaction, where one species has evolved to mimic another, to the advantage of the
copying species but to the detriment of the species being mimicked.
Neutralism[edit]
Neutralism describes the relationship between two species that interact but do not affect each other.
It describes interactions where the health of one species has absolutely no effect whatsoever on that
of the other. Examples of true neutralism are virtually impossible to prove and most ecologists (as
well as textbooks) would agree that this concept does not exist.[7] When dealing with the complex
networksof interactions presented by ecosystems, one cannot assert positively that there is
absolutely no competition between or benefit to either species. However, the term is often used to
describe situations where interactions are negligible or insignificant.
Synnecrosis is a particular case in which the interaction is so mutually detrimental that it results
in death, as in the case of some parasitic relationships.[citation needed] It is a rare and necessarily short-
lived condition as evolution selects against it. The term is seldom used.[8]
Ecological facilitation
The following two interactions can be classed as facilitative. Facilitation describes species
interactions that benefit at least one of the participants and cause no harm to either.[9]Facilitations
can be categorized as mutualisms, in which both species benefit, or commensalisms, in which one
species benefits and the other is unaffected. Much of classicecological theory (e.g., natural
selection, niche separation, metapopulation dynamics) has focused on negative interactions such as
predation and competition, but positive interactions (facilitation) are receiving increasing focus in
ecological research.
Commensalism
Commensalism benefits one organism and 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. A good example is a remora living with a shark. Remoras eat leftover food
from the shark. The shark is not affected in the process, as remoras eat only leftover food of the
shark, which does not deplete the shark's resources.
Mutualism
Pollination illustrates mutualism between flowering plants and their animal pollinators.
Mutualism is an interaction between two or more species, where species derive a mutual benefit, for
example an increased carrying capacity. Similar interactions within a species are known as co-
operation. Mutualism may be classified in terms of the closeness of association, the closest being
symbiosis, which is often confused with mutualism. One or both species involved in the interaction
may beobligate, meaning they cannot survive in the short or long term without the other species.
Though mutualism has historically received less attention than other interactions such as
predation,[14] it is very important subject in ecology. Examples include cleaner
fish, pollination andseed dispersal, gut flora, Müllerian mimicry and nitrogen fixation by bacteria in
the root nodules of legumes.
Symbiosis
The term symbiosis (Greek: living together) can be used to describe various degrees of close
relationship between organisms of different species. Sometimes it is used only for cases where both
organisms benefit; sometimes it is used more generally to describe all varieties of relatively tight
relationships, i.e. even parasitism, but not predation. Some even go so far as to use it to describe
predation. It can be used to describe relationships where one organism lives on or in another, or it
can be used to describe cases where organisms are related by mutual stereotypic behaviors.
In either case, symbiosis is much more common in the living world and much more important than is
generally assumed. Almost every organism has many internal parasites. A large percentage
of herbivores have mutualistic gut fauna that help them digest plant matter, which is more difficult to
digest than animal prey. Coral reefs are the result of mutalisms between coral organisms and
various types of algae that live inside them. Most land plants and thus, one might say, the very
existence of land ecosystems rely on mutualisms between the plants, which fix carbon from the air,
and Mycorrhyzal fungi that help in extracting minerals from the ground. The evolution of
alleukaryotes (plants, animals, fungi, protists) is believed to have resulted from a symbiosis between
various sorts of bacteria: endosymbiotic theory.
Competition
Male-male interference competition in red deer.
Main article: Competition (biology)
Competition can be defined as an interaction between organisms or species, in which the fitness of
one is lowered by the presence of another. Limited supply of at least one resource (such
as food, water, and territory) used by both usually facilitates this type of interaction, although the
competition may also exist over other 'amenities', such as females for reproduction (in case of male
organisms of the same species). Competition is one of many interacting biotic and abiotic factors
that affect community structure. Competition among members of the same species is known
as intraspecific competition, while competition between individuals of different species is known
asinterspecific competition.
Interspecific competition is normally not as fierce as intraspecific competition, unless in case of a
sudden drastic change. However, it is the most conspicuous competition in grasslands, where, for
example, cheetahs and hyenas are often killed by lion prides. Competition is not always a
straightforward, direct interaction either, and can occur in both a direct and indirect fashion.
Competition between species at the same trophic level of an ecosystem, who have common
predators, increases drastically if the frequency of the common predator in thecommunity is
decreased by a large margin. The magnitude of competition therefore depends on many factors in
the same ecosystem.
According to the competitive exclusion principle, species less suited to compete for resources should
either adapt or die out. According to evolutionary theory, this competition within and between
species for resources plays a critical role in natural selection.
