Community Definition and Concept
In biological terms, a community is defined as a population of different species of organisms interacting in a common Environment (Habitat). A group of organisms is a population of species in a specific region at a specific time.
Different populations have different characteristics such as natality, age structure, growth dynamics and others.
A population changes the genetic structure over time and the process is called ecological succession. So, the community is dynamic as it changes over time. Communities may be small with few species or large with several species populations.
Their interactions are called interspecific interactions that affect the distribution, abundance i.e. number of each species, and the existence of members of a community.
For example, a forest is a biological community where various species of animals, plants, bacteria and fungi are inhabitants and constitute a community.
In a community, most organisms are interdependent for food. This dependency on each other is represented by a food chain where each organism occupies a specific place and is known as a trophic level.
For instance, Predators like eagles feed on herbivores. Scavengers like vultures prey on dead animals for food.
A community includes populations of different species of organisms. But it does not include two populations of the same species.
Types of Interactions
Organisms undergo a rich array of interactions. The types of interactions at the reproductive and behavioral level are as follows:
Predation (+/- Interaction): A member of a species - predator eats a member of another species - prey. It is beneficial for the predator only.
Mutualism (+/+ Interaction): It involves a long-term interaction between two species where both species get the benefit.
Parasitism (+/- Interaction): A long-term association between two species that is beneficial for one and harmful for another.
Competition(-/- Interaction): Species compete for limited resources. Competition affects both participants negatively. It involves a mutually negative interaction among species of organisms with limited resources.
The result of interactions changes as the environment changes. Some of these interactions may increase diversity, while others may decrease it. Diversity is one of the most important characteristics of a community.
Structure of Community
Community structure is the composition of a community that includes the number of species and their relative numbers. The structure of a community is based on its species richness. Communities can be different in terms of types of species and the number of species they consist of.
Many factors affect the community’s structure for instance abiotic factors (non-living), interactions, disturbances, and other events.
There are two important measures to describe the composition of a Community:
1. Species Richness: It represents the number of different species in a community. If there are 252525 species in a community, and 250250250 species in another, the second community has high species richness. Rich communities are found in areas that have lots of solar energy, warm temperatures, heavy rainfall, and little seasonal change.
2. Species Diversity: It is a function of the number of species in the community i.e. species richness and their relative species. Larger numbers of species tend to have higher species diversity.
Foundation and Keystone Species
Community structure is affected by some special species. These special species are foundation and keystone species.
Foundation Species
Often, foundation species modify the environment to support the other organisms in the community. For example, Kelp (brown algae) is a foundation species that create environments for the survival of other organisms in the kelp forest community.
Keystone Species
A keystone species affects community structure disproportionately related to its abundance. Keystone species are more likely to belong to higher trophic levels. The 'Pisaster ochraceous also known as purple sea star is an example of a keystone species.
Categorization
The communities are categorized in various ways. Categorization can be qualitative or quantitative based. For example, quality-based plant communities are dependent on the availability of water, light, etc.
Communities based on water - hydrophytic - aquatic habitats, mesophytic - moderately and xerophytic.
Communities based on abundant light: heliophytes and sciophytes.
In a trophical rainforest, we find giant trees as high as 40m and obtain sunlight. They support each other for survival. This is also an example of a community.
Community Dynamics
Communities are dynamic systems as they change over time. The changes are slow and moderate but need to observe at regular intervals for a long period. For example changes in plant communities occur seasonally at every place.
The process of change in a community and its environment over time is known as “ecological succession”.
How Disturbances Affect Communities
There are other phenomena also than species interactions through which a community may change such as dispersal or the movement from one place to another.
Dispersal means a community in an area can influence a community composition at some other place.
For instance, the composition of lizards on islands changes dramatically following hurricanes. Animals are killed in floods during hurricanes and float from one island to another during and after the storm.
Many natural phenomena and disturbances, like forest fires, no doubt, are destructive, but they are natural occurrences that bring changes.
Threats to biological communities
Due to the increasing population and the rising demand for humans, the earth’s carrying capacity is eventually decreasing with time. This has created threats to the survival of biological communities.
These threats can be categorized as follows:
Human-induced threats and loss of habitat
Due to the increasing human population and resign consumerism culture demands for natural resources has also been increasing. To satisfy this demand, industries and various organizations have been destroying the natural habitat of several communities. For instance, for medicinal purposes, the horns of rhinos are in great demand and thus they are poached on a very large scale.
Deforestation and man-animal conflict
The process of clearing the existing forest is known as deforestation and this results in indirect loss of habitat for several natural species. This has also resulted in an increasing number of man-animal conflicts in recent times. For instance, the number of leopards coming towards human settlements has increased in the past few years.
Desertification
The process by which fertile land becomes a desert is known as desertification. It usually happens due to deforestation, drought, etc. The newly formed desserts after the process of desertification are not able to hold a large variety of species thus reducing species richness and affecting the structure of the community directly.
Climate change
This is the single biggest change affecting the whole of biodiversity and also biological communities. Temperatures have been rising constantly and have impacted climate over the years. This has led several animal and plants species towards extinction. This affects the biological communities directly.
FAQs on Community in Biology
1. What is the stability of a Community? Does Diversity increase stability?
Stability is a measure of a community's ability. It tells the ability to return to a condition that was before disturbance.
When many different species inhabit an area, the resources are optimally used. In doing so, the community is strong because when the abundance of one species decreases, for instance during a drought, the abundance of more drought-tolerant organisms increases.
2. What are the factors that affect the structure of the Community?
Factors to shape community structure
Climate Patterns and Geography of the Location - Distance from the equator, variation in temperature, Island or mainland communities etc
Heterogeneity (Patchiness) - Heterogeneity refers to more variation in the environment that allows greater species richness because of various habitats to be occupied.
The Frequency of Disturbances - Disruptive events such as storms, landslides, fires affect the community structure. Communities with a medium level of disturbance would have greater species diversity than communities with frequent or rare disturbances.
Type of Interactions between Organisms - Interactions between organisms such as competition, predation, mutualism has the potential to shape a community.
3. How is a community different from an ecosystem?
Ecological community and ecological ecosystems are related concepts but they have their differences. A biological community consists of living things i.e. biotic components living together and interacting with each other. Whereas an ecological ecosystem consists of both living as well as the non-living things that are it consists of both abiotic as well as biotic factors.
The ecological community has producers, consumers and decomposers as the basic biotic components. The ecological ecosystem has the same biotic component as a community in addition to abiotic components like climatic factors, social factors and edaphic factors.
Examples of Ecological Communities: bird communities, grassland communities, etc
Examples of the Ecological Ecosystem: Stillwater ecosystem, taiga ecosystem
4. What is the structure of the community in biology?
In biology, community structure can be defined as the composition of a community that includes a variety of species and their relative members. The structure of s community can be determined by estimating species richness. Any particular biological community can be distinguished in terms of the types of species it contains and the number of species present in it.
The structure of a community is not independent rather it can get affected by a number of factors such as abiotic factors (like climatic conditions, soil conditions, etc), interactions, disturbances (like the introduction of an alien species), and other events.
5. What are the foundation and keystone species in the community in biology and also what are their examples?
Foundation species have a very crucial role in structuring a community. In simple words, it can be defined as the species which initiates the process of building an ecological community. It plays a very important role in supporting other species in an ecosystem. It can occupy any trophic level in the biological pyramid. A few examples of foundation species are corals, earthworms, beavers, etc.
A keystone species can be defined as an organism that has a very profound effect on the entire community. It enjoys a disproportionate amount of importance in comparison to other species present in the ecosystem because of its overall effect. Due to this large amount of effort ate put into conserving it. Some examples of keystone species are bees, tiger sharks, otters, etc.
