Table of Contents
The assembly of interacting organisms in a particular time and area is referred to as a community. The members of the community affect the abundance, distribution, adaptation, and existence of each other due to their interactions. The community has two major properties, community structure, and community function.
The structure of community includes its biotic components whereas the function is characterized by energy flow, resilience, and resistance of the community. The size of a community may vary, it can be very small as in a pond or can be huge such as biomes.
What is Community?
A group of organisms where the members share some common interests, language, tradition, manners, laws, or culture is described as a community. In biology, the community can be defined as a group of interacting organisms.
Not all the members of a community need to be from the same species. In a biological community, the members can be from different species that share a common habitat and interact with each other. The interaction can be through symbiotic relationships, mutualism, commensalism, or competition.
In ecology, an association or group of organisms from different species that co-inhabit a geographical for over a particular time is called a community. In other words, the assemblage of living organisms having a symbiotic relationship and living as an ecological unit is called an ecological community.
The term community is derived from the Latin word communitatem, meaning society or fellowship. The community is called biocenosis is ecology. A German zoologist and ecologist Karl Mobius coin the word community in 1877.
Community vs Ecosystem
Both the terms are different but related to each other. A group of organisms interacting and living with each other is defined as a community while an ecosystem comprises both living and non-living things that function as a unit and are interconnected for energy and biogeochemical cycling.
However the definition of community does not include abiotic factors but the structure, pattern, and abundance of the community get affected by these abiotic factors. Examples of the community include Grassland communities, Bird communities, deciduous forest communities, etc. while the ecosystem includes forest ecosystem, Taiga ecosystem, Stillwater ecosystem, etc.
The assemblages of organisms in any community can overlap sometimes thus recognition of a community can quite be a confounding task. The properties include community structure and community function. The biotic components of a community are described as a community structure that includes species abundance and diversity as well as the trophic relationships between the members of the community.
Community function includes energy flow, resilience, and resistance. The energy flows through various trophic levels in a food chain that include two important attributes such as resilience and resistance. The biotic and abiotic changes influence the assemblage of organisms in a community.
The community must be able to resist these changes to become a stable community. To measure the point of stability or equilibrium is quite difficult, which sometimes could take several years of observation.
The major characteristics of a community include (i) species diversity (ii) species interactions (iii) spatial structure (iv) periodicity, (v) ecotone.
i. Species Diversity
The complexity of species in a community is called diversity. It can be calculated by species richness or species evenness. The number of species living together in a particular area is defined as species richness. Due to favorable environmental conditions, areas near the equator have the greatest species richness whereas the poles have the lowest species richness.
Relative species abundance is another important measure that refers to the number of individuals in a species with respect to the number of individuals in all species. The primary producers represent the foundation species in a community that produces chemical energy for light energy.
Producers store this energy in form of organic molecules such as carbohydrates and serve as a food source for consumers of the ecosystem. Decomposers get their energy from those consumers and also decompose the dead organic matter. A community comprises a dominant species, which is referred to as ecological dominants. Often, plants are the dominants thus the community is named based on dominant plants such as Oak forest community, grass community.
Keystone species are another special species that are described as keystones because of their important role. They are important to maintaining biodiversity and upholding the structure of the community. An example is Banded tetra fish, which is a source of phosphorus.
ii. Species Interactions
Species in a community may interact directly or indirectly. When the species are in direct physical contact, it is called direct interaction while when an intermediate species mediate the interaction, it is considered as indirect interaction. Other types of interaction are linear and circular. The example of linear interaction is competitive hierarchy whereas circular interaction includes a competitive network.
iii. Spatial Structure
The structure is represented through stratification or zonation. The zonation includes the division of a community for example a lake community is divided into a littoral zone, limnetic zone, and profundal zone. Different types of organisms are present in each zone. Another structure in stratification, which is more common and includes the formation of different strata. The example includes the sea, which is divided into upper and lower strata. Autotrophs are chiefly inhabited in the upper stratum whereas the lower stratum includes heterotrophs.
Periodicity predicts the rhythmic biological activities in a community. The examples are diurnal organisms that will be active during the day and nocturnal organisms that become active at night. Many organisms in the community are influenced by circadian rhythms.
The presence of ecotone represents the adjacent communities. Thus, the ecotone serves as a boundary between two communities. It is also known as a transition state, which is comparatively denser and richer than the two adjacent communities. Edge species are the species that are restricted at the ecotone. Example: estuary where the rivers meet the sea.
The community can effect by various natural disturbances such as volcanic eruption, fire, earthquake, etc. if a stable community fails to bounce back to its equilibrium, the original community could be replaced with a new one. This process is known as ecological succession.
The directional and progressive change of a given area is defined as ecological succession. It can be of two types: primary and secondary succession. When a community establishes in a newly formed land, it is called primary succession. On the other hand, when a community replaces the first one after any disturbance, it is termed secondary succession.
Generally, the pioneer species such as grasses and perennials start this pattern. Higher plant species such as shrubs and pines grow after some time that is referred to as intermediate species. At last, the advanced plant species such as Oak and hickory grow and reach stability, which is called a climax community.
Types of Communities
Communities can be classified as major communities and minor communities. Major communities span larger geographic areas whereas minor communities span relatively smaller areas. Minor communities are more or less dependent on their adjacent communities thus they may make up a larger community together.
The other classification criteria are an open or closed community. When the organism is distantly placed and a new invasion is possible in the community, it is referred to as an open community. On the other hand, a closed community consists of closely placed organisms where further invasion is not possible.
Importance of Community
Community allows species interaction, thus it is very important. There are various reasons behind the interaction of species such as nutrition. For example, heterotrophs are not capable to perform photosynthesis thus they depend upon autotrophs for their nutrition.
Plants can perform photosynthesis and make their own food however they also depend on animals for CO2, which is released as a by-product by animals. Some animals also interact with other species for other requirements such as shelter. For example, a tree provides habitat or shelter to many other organisms, such as birds, lichens, insects, and arachnids.
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