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In ecology, a community is a group or
association Association may refer to: *Club (organization), an association of two or more people united by a common interest or goal *Trade association, an organization founded and funded by businesses that operate in a specific industry *Voluntary association ...
of
population Population typically refers the number of people in a single area whether it be a city or town, region, country, or the world. Governments typically quantify the size of the resident population within their jurisdiction by a process called a ...
s of two or more different
species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individu ...

species
occupying the same geographical area at the same time, also known as a
biocoenosis Aquatic ecosystem, aquatic and Ecoregion#Terrestrial, terrestrial food web. A biocenosis (UK English, ''biocoenosis'', also biocenose, biocoenose, biotic community, biological community, Community (ecology), ecological community, life assemblage ...
, biotic community, biological community, ecological community, or life assemblage. The term community has a variety of uses. In its simplest form it refers to groups of organisms in a specific place or time, for example, "the fish community of Lake Ontario before industrialization". Community ecology or synecology is the study of the interactions between species in communities on many spatial and temporal scales, including the distribution, structure, abundance,
demography Demography (from prefix ''demo-'' from Ancient Greek Ancient Greek includes the forms of the used in and the from around 1500 BC to 300 BC. It is often roughly divided into the following periods: (), Dark Ages (), the period ...

demography
, and
interaction Interaction is a kind of action that occurs as two or more objects have an effect upon one another. The idea of a two-way effect is essential in the concept of interaction, as opposed to a one-way causal effect. Closely related terms are interac ...
s between coexisting populations. The primary focus of community ecology is on the interactions between populations as determined by specific
genotypic Here the relation between genotype and phenotype is illustrated, using a Punnett square, for the character of petal colour in a pea plant. The letters B and b represent alleles for colour and the pictures show the resultant flowers. The punnet s ...
and
phenotypic In genetics Genetics is a branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular inter ...
characteristics. Community ecology also takes into account
abiotic factors
abiotic factors
that influence species distributions or interactions (e.g. annual temperature or
soil pH Soil pH is a measure of the acidity An acid is a molecule or ion capable of donating a proton (hydrogen ion H+) (a Brønsted–Lowry acid–base theory, Brønsted–Lowry acid), or, alternatively, capable of forming a covalent bond with an ...
). For example, the plant communities inhabiting
desert A desert is a barren area of landscape where little precipitation occurs and, consequently, living conditions are hostile for plant and animal life. The lack of vegetation exposes the unprotected surface of the ground to the processes of ...

desert
s are very different from those found in
tropical rainforest Tropical rainforests are rainforest Rainforests are characterized by a closed and continuous tree canopy Canopy may refer to: Plants * Canopy (biology), aboveground portion of plant community or crop (including forests) * Canopy (grape ...

tropical rainforest
s due to differences in annual precipitation. Humans can also affect community structure through habitat disturbance, such as the introduction of
invasive species An invasive species is an introduced organism that becomes overpopulated and negatively alters its new environment. Although their spread can have beneficial aspects, invasive species adversely affect the invaded habitat Ibex in an ...
. On a deeper level the meaning and value of the community concept in ecology is up for debate. Communities have traditionally been understood on a fine scale in terms of local processes constructing (or destructing) an assemblage of species, such as the way climate change is likely to affect the make-up of grass communities. Recently this local community focus has been criticised.
Robert RicklefsDr Robert Eric Ricklefs (born June 6, 1943) is an American ornithologist and ecologist. He is the Curators' Professor of Biology at the University of Missouri, St. Louis. Education Born in 1943, he graduated with a Bachelor of Science from Stanford ...
has argued that it is more useful to think of communities on a regional scale, drawing on evolutionary
taxonomy Taxonomy (general) is the practice and science of classification of things or concepts, including the principles that underlie such classification. The term may also refer to a specific classification scheme. Originally used only about biological ...
and
biogeography Biogeography is the study of the distribution of species and ecosystems in geography, geographic space and through evolutionary history of life, geological time. Organisms and biological communities often vary in a regular fashion along geograp ...

biogeography
, where some species or
clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyly, monophyletic – that is, composed of a common ancestor and all its lineage (evolution), lineal descendants - on a phylogenetic tree. R ...

clade
s evolve and others go extinct.


Organisation


Niche

Within the community, each species occupies a
niche Niche may refer to: Science *Developmental niche{{third-party, date=October 2020 The developmental niche is a theoretical framework for understanding and analyzing how culture Culture () is an umbrella term which encompasses the social behav ...

niche
. A species' niche determines how it interacts with the environment around it and its role within the community. By having different niches species are able to coexist. This is known as niche partitioning. For example, the time of day a species hunts or the prey it hunts. Niche partitioning reduces competition between species. Such that species are able to coexist as they suppress their own growth more than they limit the growth of other species. The competition within a species is greater than the competition between species. Intraspecific competition is greater than interspecific. The number of niches present in a community determines the number of species present. If two species have the exact same niche (e.g. the same food demands) then one species will outcompete the other. The more niches filled, the higher the
biodiversity Biodiversity is the biological variety and Genetic variability, variability of life, life on Earth. Biodiversity is a measure of variation at the Genetics, genetic, species, and ecosystem level. Terrestrial biodiversity is usually greater near ...

biodiversity
of the community.


Trophic Level

A species’
trophic level The trophic level of an organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular int ...
is their position in the food chain or web. At the bottom of the food web are
autotroph An autotroph or primary producer is an organism that produces complex organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bo ...
s, also known as
primary producer Primary or primaries may refer to: Arts, entertainment, and media Music Groups and labels * Primary (band) Primary were an Australian electronic rock band which formed in 1995 the Fonti brothers: Jamie on keyboards and Sean on bass guitar (b ...
. Producers provide their own energy through
photosynthesis Photosynthesis is a process used by plants and other organisms to convert Conversion or convert may refer to: Arts, entertainment, and media * Conversion (Doctor Who audio), "Conversion" (''Doctor Who'' audio), an episode of the audio drama ' ...

photosynthesis
or
chemosynthesis In biochemistry, chemosynthesis is the biological conversion of one or more carbon-containing molecules (usually carbon dioxide or methane) and nutrients into organic matter using the oxidation of inorganic compounds (e.g., hydrogen gas, hydroge ...
, plants are primary producers. The next level is
herbivores A herbivore is an animal Animals (also called Metazoa) are multicellular A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All ...
(primary consumers), these species feed on vegetation for their energy source. Herbivores are consumed by
omnivores An omnivore () is an animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular ...
or
carnivores A carnivore , meaning "meat Meat is animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume orga ...
. These species are secondary and tertiary consumers. Additional levels to the trophic scale come when smaller omnivores or carnivores are eaten by larger ones. At the top of the food web is the
apex predator The great white shark (bottom) was originally considered the apex predator of the ocean; however, the killer whale (top) has proven to be a predator of the shark. An apex predator, also known as an alpha predator or top predator, is a predator ...
, this animal species is not consumed by any other in the community. Herbivores, omnivores and carnivores are all
heterotroph A heterotroph (; from Ancient Greek Ancient Greek includes the forms of the Greek language Greek ( el, label=Modern Greek Modern Greek (, , or , ''Kiní Neoellinikí Glóssa''), generally referred to by speakers simply as Greek ...
s. A basic example of a food chain is; grass → rabbit → fox. Food chains become more complex when more species are present, often being food webs. Energy is passed up through trophic levels. Energy is lost at each level, due to ecological inefficiencies. The trophic level of an organism can change based on the other species present. For example, tuna can be an apex predator eating the smaller fish, such as mackerel. However, in a community where a shark species is present the shark becomes the apex predator, feeding on the tuna.
Decomposers Decomposers are organisms that break down dead or decaying organisms, they carry out decomposition, a process possible by only certain kingdoms, such as fungi. Like herbivores and predator Predation is a biological interaction where one o ...
play a role in the trophic pyramid. They provide energy source and nutrients to the plant species in the community. Decomposers such as fungi and bacteria recycle energy back to the base of the food web by feeding on dead organisms from all trophic levels.


Guild

A
guild A guild is an association of artisan Wood carver in Bali An artisan (from french: artisan, it, artigiano) is a skilled craft worker who makes or creates material objects partly or entirely by hand. These objects may be functiona ...
is a group of species in the community that utilise the same resources in a similar way. Organisms in the same guild experience competition due to their shared resource. Closely related species are often in the same guild, due to traits inherited through
common descent Common descent is a concept in evolutionary biology Evolutionary biology is the subfield of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chem ...
from their
common ancestor Common descent is a concept in evolutionary biology Evolutionary biology is the subfield of biology that studies the evolution, evolutionary processes (natural selection, common descent, speciation) that produced the Biodiversity, diversity ...
. However, guilds are not exclusively composed of closely related species. Carnivores, omnivores and herbivores are all basic examples of guilds. A more precise guild would be vertebrates that forage for ground dwelling
arthropod An arthropod (, (gen. ποδός)) is an invertebrate animal having an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Euarthropoda,Reference showing that Euarthropoda is a phylum: ...
s, this would contain certain birds and mammals. Flowering plants that have the same pollinator also form a guild.


Influential species

Certain species have a greater influence on the community through their direct and indirect interactions with other species. The loss of these species results in large changes to the community, often reducing the stability of the community. Climate change and the introduction of invasive species can affect the functioning of key species and thus have knock-on effects on the community processes.


Foundation species

Foundation species In ecology Ecology (from el, οἶκος, "house" and el, -λογία, label=none, "study of") is the study of the relationships between living organisms, including humans, and their physical environment. Topics of interest include the biod ...
largely influence the population, dynamics and processes of a community. These species can occupy any trophic level but tend to be producers. Red mangrove is a foundation species in marine communities. The mangrove's root provides nursery grounds for young fish, such as snappers. Whitebark pine (''
Pinus albicaulis ''Pinus albicaulis'', known by the common names whitebark pine, white bark pine, white pine, pitch pine, scrub pine, and creeping pine, is a conifer tree native to the mountains of the western United States and Canada, specifically subalpine ar ...
'') is a foundation species. Post fire disturbance the tree provides shade (due to its dense growth) enabling the regrowth of other plant species in the community, This growth prompts the return of invertebrates and microbes which are needed for decomposition. Whitebark pine seeds provide food for grizzly bears.


Keystone species

Keystone species A keystone species is a species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group o ...
have a disproportionate influence on the community than most species. Keystone species tend to be at the higher trophic levels, often being the apex predator. Removal of the keystone species causes top-down
trophic cascadeTrophic cascades are powerful indirect interactions that can control entire ecosystems, occurring when a trophic level in a food web is suppressed. For example, a top-down cascade will occur if predators are effective enough in predation to reduce th ...

trophic cascade
s. Wolves are keystone species, being an apex predator. In
Yellowstone National Park Yellowstone National Park is an American national park located in the western United States, largely in the northwest corner of Wyoming and extending into Montana and Idaho. It was established by the U.S. Congress and signed into law by ...

Yellowstone National Park
the loss of the wolf population through overhunting resulted in the loss of biodiversity in the community. The wolves had controlled the number of
elk The elk (''Cervus canadensis''), also known as the wapiti, is one of the largest species within the deer Deer or true deer are ed s forming the Cervidae. The two main groups of deer are the , including the , the (wapiti), the , a ...

elk
s in the park, through predation. Without the wolves the elk population drastically increased, resulting in overgrazing. This negatively affected the other organisms in the park; the increased grazing from the elks removed food sources from other animals present. Wolves have since been reintroduced to return the park community to optimal functioning. See
Wolf reintroduction Wolf reintroduction involves the reintroduction, re-establishment of a portion of gray wolf, gray wolves in areas where native wolves have been Local extinction, extirpated. More than 30 subspecies of Canis lupus, subspecies of ''Canis lupus'' have ...
and
History of wolves in Yellowstone The History of wolves in Yellowstone chronicles the extirpation, absence and reintroduction Species reintroduction is the deliberate release of a species In biology, a species is the basic unit of biological classification, classification an ...
for more details on this case study. A marine example of a keystone species is ''
Pisaster ochraceus ''Pisaster ochraceus'', generally known as the purple sea star, ochre sea star, or ochre starfish, is a common seastar Starfish or sea stars are star-shaped echinoderms belonging to the class (biology), class Asteroidea. Common usage frequen ...
''. This starfish controls the abundance of '' Mytilus californianus'', allowing enough resources for the other species in the community.


Ecological engineers

An
ecosystem engineer An ecosystem engineer is any species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest gr ...
is a species that maintains, modifies and creates aspects of a community. They cause physical changes to the habitat and alter the resources available to the other organisms present. Dam building beavers are ecological engineers. Through the cutting of trees to form dams they alter the flow of water in a community. These changes influence the vegetation on the
riparian zone A riparian zone or riparian area is the interface between land and a river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases a river flows into the ground an ...
, studies show biodiversity is increased. Burrowing by the beavers creates channels, increasing the connections between habitats. This aids the movement of other organisms in the community such as frogs.


Theories of community structure

Community structure is the composition of the community. It is often measured be measured through
biological network A biological network is any network Network, networking and networked may refer to: Science and technology * Network theory Network theory is the study of Graph (discrete mathematics), graphs as a representation of either symmetric relatio ...
s, such as
food web A food web is the natural interconnection of food chains and a graphical representation of what-eats-what in an ecological community. Another name for food web is Consumer-resource systems, consumer-resource system. Ecologists can broadly lump a ...

food web
s.


Holistic theory

Holistic theory refers to the idea that a community is defined by the interactions between the organisms in it. All species are interdependent, each playing a vital role in the working of the community. Due to this communities are repeatable and easy to identify, with similar abiotic factors controlling throughout.
Frederic Clements Frederic Edward Clements (September 16, 1874 – July 26, 1945) was an American plant ecologist and pioneer in the study of vegetation Ecological succession, succession. Biography Born in Lincoln, Nebraska, he studied botany at the University of N ...
developed the holistic (or organismic) concept of community, as if it was a
superorganism A superorganism or supraorganism is a group of synergetically interacting organisms of the same species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a ...
or discrete unit, with sharp boundaries. Clements proposed this theory after noticing that certain plant species were regularly found together in habitats, he concluded that the species were dependent on each other. Formation of communities is non-random and involves
coevolution In biology, coevolution occurs when two or more species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined ...
. The Holistic theory stems from the greater thinking of
Holism Holism (from Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approximately 10.7 million as ...
; which refers to a system's with many parts all of which are required for the functioning of the system.


Individualistic theory

Henry Gleason Henry Allan Gleason (1882–1975) was an American ecologist Ecology (from el, οἶκος, "house" and el, -λογία, label=none, "study of") is the study of the relationships between living organisms, including humans, and their physic ...
developed the individualistic (also known as open or continuum) concept of community, with the abundance of a population of a species changing gradually along complex environmental gradients. Each species changes independently in relation to other species present along the gradient. Association of species is random and due to coincidence. Varying environmental conditions and each species' probability of arriving and becoming established along the gradient influence the community composition. Individualistic theory proposes that communities can exist as continuous entities, in addition to the discrete groups referred to in the holistic theory.


Neutral theory

Stephen P. Hubbell introduced the neutral theory of ecology. Within the community (or metacommunity), species are functionally equivalent, and the abundance of a population of a species changes by
stochastic Stochastic () refers to the property of being well described by a random In common parlance, randomness is the apparent or actual lack of pattern or predictability in events. A random sequence of events, symbols or steps often has no :wi ...
demographic Demography (from prefix ''demo-'' from Ancient Greek Ancient Greek includes the forms of the used in and the from around 1500 BC to 300 BC. It is often roughly divided into the following periods: (), Dark Ages (), the period ...

demographic
processes (i.e., random births and deaths). Equivalence of the species in the community leads to ecological drift. Ecological drift leads to species' populations randomly fluctuating, whilst the overall number of individuals in the community remains constant. When an individual dies, there is an equal chance of each species colonising that plot. Stochastic changes can cause species within the community to go extinct, however, this can take a long time if there are many individuals of that species. Species can coexist because they are similar, resources and conditions apply a filter to the type of species that are present in the community. Each population has the same adaptive value (competitive and dispersal abilities) and resources demand. Local and regional composition represent a balance between
speciation Speciation is the evolutionary process by which populations evolve to become distinct species. The biologist Orator F. Cook coined the term in 1906 for cladogenesis, the splitting of lineages, as opposed to anagenesis, phyletic evolution within ...

speciation
or
dispersal Dispersal may refer to: * Biological dispersal, the movement of organisms from their birth site to their breeding site, or from one breeding site to another ** Dispersal vector, forces that carry seeds for plants ** Oceanic dispersal, the movement ...
(which increase diversity), and random extinctions (which decrease diversity).


Interspecific interactions

Species
interact Interact may refer to: * Interaction Interaction is a kind of action that occurs as two or more objects have an effect upon one another. The idea of a two-way effect is essential in the concept of interaction, as opposed to a one-way causal ef ...
in various ways: competition,
predation Predation is a biological interaction In ecology Ecology (from el, οἶκος, "house" and el, -λογία, label=none, "study of") is the study of the relationships between living organisms, including humans, and their physical en ...

predation
,
parasitism Parasitism is a close relationship between species In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, ...

parasitism
, mutualism,
commensalism Commensalism is a long-term biological interaction In ecology Ecology (from el, οἶκος, "house" and el, -λογία, label=none, "study of") is the study of the relationships between living organisms, including humans, and their phy ...

commensalism
, etc. The organization of a biological community with respect to ecological interactions is referred to as community structure.


Competition

Species can
compete Competition arises whenever two or more parties strive for a common goal which cannot be shared: where one's gain is the other's loss (an example of which is a zero-sum game). Competition includes rivalry between entities such as organisms, ind ...
with each other for finite
resources Resource refers to all the materials available in our environment which help us to satisfy our needs and wants. Resources can broadly be classified upon their availability — they are classified into renewable A renewable resource, also know ...
. It is considered to be an important limiting factor of
population size In population genetics and population ecology, population size (usually denoted ''N'') is the number of individual organisms in a population. Population size is directly associated with amount of genetic drift, and is the underlying cause of effects ...
,
biomass Biomass is plant or animal material used as fuel to produce electricity Electricity is the set of physical phenomena associated with the presence and motion Image:Leaving Yongsan Station.jpg, 300px, Motion involves a change in position ...
and
species richness File:Global Amphibian Richness Grids, 2015 Release, All Amphibians (28794889801).jpg, 300px, Global amphibian richness (2015) Species richness is the number of different species represented in an community (ecology), ecological community, landscape ...
. Many types of competition have been described, but proving the existence of these interactions is a matter of debate. Direct competition has been observed between individuals, populations and species, but there is little evidence that competition has been the driving force in the evolution of large groups. # Interference competition: occurs when an individual of one species directly interferes with an individual of another species. This can be for food or for territory. Examples include a lion chasing a hyena from a kill, or a plant releasing
allelopathic Allelopathy is a biological phenomenon by which an organism produces one or more biochemicals that influence the germination, growth, survival, and reproduction of other organisms. These biochemicals are known as allelochemicals and can have bene ...
chemicals to impede the growth of a competing species. # Apparent competition: occurs when two species share a predator. For example, a cougar preys on woodland caribou and deer. The populations of both species can be depressed by predation without direct exploitative competition. # Exploitative competition: This occurs via the consumption of resources. When an individual of one species consumes a resource (e.g., food, shelter, sunlight, etc.), that resource is no longer available to be consumed by a member of a second species. Exploitative competition is thought to be more common in nature, but care must be taken to distinguish it from the apparent competition. An example of exploitative competition could be between herbivores consuming vegetation; rabbit and deer both eating meadow grass. Exploitative competition varies: ::* complete symmetric - all individuals receive the same amount of resources, irrespective of their size ::*perfect size symmetric - all individuals exploit the same amount of resource per unit biomass ::*absolute size-asymmetric - the largest individuals exploit all the available resource. ::The degree of size asymmetry has major effects on the structure and diversity of ecological communities


Predation

Predation Predation is a biological interaction In ecology Ecology (from el, οἶκος, "house" and el, -λογία, label=none, "study of") is the study of the relationships between living organisms, including humans, and their physical en ...

Predation
is hunting another species for food. This is a positive-negative interaction, the predator species benefits while the prey species is harmed. Some predators kill their prey before eating them, also known as kill and consume. For example, a hawk catching and killing a mouse. Other predators are parasites that feed on prey while alive, for example, a vampire bat feeding on a cow. Parasitism can however lead to death of the host organism over time. Another example is the feeding on plants of
herbivore A herbivore is an animal Animals (also called Metazoa) are organisms that form the Animalia. With few exceptions, animals , , are , can , and grow from a hollow sphere of , the , during . Over 1.5 million animal have been —of ...
s, for example, a cow grazing. Predation may affect the population size of predators and prey and the number of species coexisting in a community. Predation can be specialist, for example the least weasel predates solely on the field vole. Or generalist, e.g. polar bear primarily eats seals but can switch diet to birds when seal population is low. Species can be solitary or group predators. The advantage of hunting in a group means bigger prey can be taken, however, the food source has to be shared. Wolves are group predators, whilst tigers are solitary. Predation is density dependant, often leading to population cycles. When prey is abundant predator species increases, thus eating more prey species and causing the prey population to decline. Due to lack of food the predator population declines. Due to lack of predation the prey population increases. See
Lotka–Volterra equations The Lotka–Volterra equations, also known as the predator–prey equations, are a pair of first-order nonlinear In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathe ...
for more details on this. A well-known example of this is
lynx A lynx (; plural lynx or lynxes) is any of the four species (the Canada lynx, Iberian lynx, Eurasian lynx, or bobcat The bobcat (''Lynx rufus''), also known as the red lynx, is a medium-sized cat The cat (''Fel ...

lynx
-
hare Hares and jackrabbits are Leporidae, leporids belonging to the genus ''Lepus''. Hares are classified in the same Family (biology), family as rabbits. They have similar herbivorous diets, but are generally larger in size than rabbits, have proport ...

hare
population cycles seen in the north. Predation can result in coevolution –
evolutionary arms race In evolutionary biology Evolutionary biology is the subfield of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biolo ...
, prey adapts to avoid predator, predator evolves. For example, a prey species develops a toxin that will kill its predator, predator evolves resistance to the toxin making it no longer lethal.


Mutualism

Mutualism is an interaction between species in which both benefit. An example is ''
Rhizobium ''Rhizobium'' is a genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses ...
'' bacteria growing in nodules on the roots of legumes. This relationship between plant and bacteria is
endosymbiotic An endosymbiont or endobiont is any organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the Life#Biology, properties of life. It is a synony ...
, the bacteria living on the roots of the legume. The plant provides compounds made during photosynthesis to the bacteria, that can be used as an energy source. Whilst Rhizobium is a
nitrogen fixing Nitrogen fixation is a chemical process by which molecular nitrogen Nitrogen is the chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific st ...
bacteria, providing amino acids or ammonium to the plant. Insects pollinating the flowers of
angiosperm Flowering plants include multiple members of the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ...

angiosperm
s, is another example. Many plants are dependent on
pollination Pollination is the transfer of pollen Pollen is a powdery substance consisting of pollen grains which are Sporophyte, microsporophytes of spermatophyta, seed plants, which produce male gametes (sperm cells). Pollen grains have a hard coat ...

pollination
from a pollinator. A pollinator transfers pollen from the male flower to the female's
stigma Stigma or plural stigmata, stigmas may refer to: * Social stigma, the disapproval of a person based on physical or behavioral characteristics that distinguish them from others Symbolism * Stigmata, bodily marks or wounds resembling the crucifix ...
. This fertilises the flower and enables the plant to reproduce. Bees, such as
honeybees A honey bee (also spelled honeybee) is a eusocial flying insect within the genus Genus (plural genera) is a taxonomic rank Taxonomy (general) is the practice and science of classification of things or concepts, including the principles t ...

honeybees
, are the most commonly known pollinators. Bees get nectar from the plant that they use as an energy source. Un-transferred pollen provides protein for the bee. The plant benefits through fertilisation, whilst the bee is provided with food.


Commensalism

Commensalism Commensalism is a long-term biological interaction In ecology Ecology (from el, οἶκος, "house" and el, -λογία, label=none, "study of") is the study of the relationships between living organisms, including humans, and their phy ...

Commensalism
is a type of relationship among organisms in which one organism benefits while the other organism is neither benefited nor harmed. The organism that benefited is called the ''commensal'' while the other organism that is neither benefited nor harmed is called the ''host''. For example, an
epiphytic 200px, '' Tillandsia bourgaei'' growing on an oak tree in Mexico An epiphyte is an organism that grows on the surface of a plant and derives its moisture and nutrients from the air, rain, water (in marine environments) or from debris accumulating a ...

epiphytic
orchid attached to the tree for support benefits the orchid but neither harms nor benefits the tree. This type of commensalism is called
inquilinism In zoology Zoology ()The pronunciation of zoology as is typically regarded as nonstandard, though it is not uncommon. is the branch of biology that studies the animal kingdom, including the anatomy, structure, embryology, evolution, Biologic ...
, the orchid permanently lives on the tree.
Phoresy hitching a ride on a fly. File:Phoresy_edited.png, A pseudoscorpion on the leg of a crane fly Phoresis or phoresy is a non-permanent, Commensalism, commensalistic interaction in which one organism (a phoront or phoretic) attaches itself to anoth ...

Phoresy
is another type of commensalism, the commensal uses the host solely for transport. Many
mite Mites are small arachnid Arachnida () is a class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Cl ...
species rely on another organism, such as birds or mammals, for dispersal. Metabiosis is the final form of commensalism. The commensal relies on the host to prepare an environment suitable for life. For example, Kelp has a root like system, called a holdfast, that attaches it to the seabed. Once rooted it provides
molluscs Mollusca is the second-largest phylum In biology, a phylum (; plural The plural (sometimes list of glossing abbreviations, abbreviated ), in many languages, is one of the values of the grammatical number, grammatical category of number ...

molluscs
, such as sea snails, with a home that protects them from predation.


Amensalism

The opposite of commensalism is amensalism, an interspecific relationship in which a product of one organism has a negative effect on another organism but the original organism is unaffected. An example is an interaction been tadpoles of the and a
freshwater snail Freshwater snails are gastropod mollusks which live in fresh water. There are many different families. They are found throughout the world in various habitats, ranging from ephemeral pools to the largest lakes, and from small seeps and springs ...
. The tadpoles consume large amounts of micro-algae. Making algae less abundant for the snail, the algae available for the snail is also of lower quality. The tadpole, therefore, has a negative effect on the snail without a gaining noticeable advantage from the snail. The tadpoles would obtain the same amount of food with or without the presence of the snail. An older, taller tree can inhibit the growth of smaller trees. A new sapling growing in the shade of a mature tree will struggle to get light for photosynthesis. The mature tree will also have a well-developed root system, enabling it to outcompete the sapling for nutrients. Growth of the sapling is therefore impeded, often resulting in death. The relationship between the two trees is amensalism, the mature tree is unaffected by the presence of the smaller one.


Parasitism

Parasitism Parasitism is a close relationship between species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined ...

Parasitism
is an interaction in which one organism, the host, is harmed while the other, the parasite, benefits. Parasitism is a
symbiosis Symbiosis (from Ancient Greek, Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different Organism, biological organisms, be it Mutualism (biolog ...

symbiosis
, a long-term bond in which the parasite feeds on the host or takes resources from the host. Parasites can live within the body such as a
tapeworm Eucestoda, commonly referred to as tapeworms, are the larger of the two subclasses Subclass may refer to: * Subclass (taxonomy), a taxonomic rank below "class" * Subclass (computer science) * Subclass (set theory) See also * Superclass (disa ...

tapeworm
. Or on the body's surface, for example
Malaria Malaria is a mosquito-borne infectious disease that affects humans and other animals. Malaria causes symptoms Signs and symptoms are the observed or detectable signs, and experienced symptoms of an illness, injury, or condition. A sign fo ...

Malaria
is a result of a parasitic relationship between a female Anopheles mosquito and ‘’
Plasmodium ''Plasmodium'' is a genus of unicellular eukaryotes that are obligate parasites of vertebrates and insects. The life cycles of ''Plasmodium'' species involve development in a Hematophagy, blood-feeding insect host (biology), host which then inj ...

Plasmodium
’’. Mosquitos get the parasite by feeding on an infected vertebrate. Inside the mosquito the plasmodium develops in the midgut's wall. Once developed to a
zygote A zygote (, ) is a eukaryotic Eukaryotes () are organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are ...

zygote
the parasite moves to the salivary glands where it can be passed on to a vertebrate species, for example humans. The mosquito acts as a
vector Vector may refer to: Biology *Vector (epidemiology) In epidemiology Epidemiology is the study and analysis of the distribution (who, when, and where), patterns and risk factor, determinants of health and disease conditions in defined pop ...
for Malaria. The parasite tends to reduce the mosquito's lifespan and inhibits the production of offspring. A second example of parasitism is
brood parasitism Brood parasites are organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interact ...
. Cuckoos regularly do this type of parasitism. Cuckoos lay their eggs in the nest of another species of birds. The host, therefore, provides for the cuckoo chick as if it was their own, unable to tell the difference. The cuckoo chicks eject the host's young from the nest meaning they get a greater level of care and resources from the parents. Rearing for young is costly and can reduce the success of future offspring, thus the cuckoo attempts to avoid this cost through brood parasitism. In a similar way to predation, parasitism can lead to an
evolutionary arms race In evolutionary biology Evolutionary biology is the subfield of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biolo ...
. The host evolves to protect themselves from the parasite and the parasite evolves to overcome this restriction.


Neutralism

Neutralism is where species interact, but the interaction has no noticeable effects on either species involved. Due to the interconnectedness of communities, true neutralism is rare. Examples of neutralism in ecological systems are hard to prove, due to the indirect effects that species can have on each other.


See also

* * * * * * * * * * * * * * * * * * * *


References


Further reading

* Akin, Wallace E. (1991). ''Global Patterns: Climate, Vegetation, and Soils''. University of Oklahoma Press. . * Barbour, Burke, and Pitts, 1987. ''Terrestrial Plant Ecology'', 2nd ed. Cummings, Menlo Park, CA. * Morin, Peter J. (1999). ''Community Ecology''. Wiley-Blackwell Press. . * Odum, E. P. (1959) ''Fundamentals of ecology''. W. B. Saunders Co., Philadelphia and London. * Ricklefs, R.E. (2005) ''The Economy of Nature'', 6th ed. WH Freeman, USA. * Ricketts, Taylor H., Eric Dinerstein, David M. Olson, Colby J. Loucks et al. ( WWF) (1999). ''Terrestrial Ecoregions of North America: a conservation assessment''. Island Press. .


External links


Community, BioMineWiki

Identify microbial species in a community, BioMineWiki


Status and Trends of the Nation's Biological Resources, USGS.
Glossary
ENTRIX Environmental Consultants. {{DEFAULTSORT:Community (Ecology) Biogeography Community ecology
Ecology Ecology (from el, οἶκος, "house" and el, -λογία, label=none, "study of") is the study of the relationships between living organisms, including humans, and their physical environment. Ecology considers organisms In biol ...
Habitat