Here is a compilation of essays on ‘Biotic Community’ for class 9, 10, 11 and 12. Find paragraphs, long and short essays on ‘Biotic Community’ especially written for school and college students.
Contents
Essay on Biotic Community
Essay Contents:
- Essay on Introduction to Biotic Community
- Essay on the Characteristics of a Biotic Community
- Essay on the Interaction among Biotic Community
- Essay on the Composition of Biotic Community
- Essay on Biotic Stability
- Essay on the Ecological Succession or Changes in a Biotic Community
Essay # 1. Introduction to Biotic Community:
The word biocoenosis, biocoenose, biocenose, biotic community, biological community, ecological community was coined by Karl Mobius in 1877. Biotic community is a group of inter dependent organisms that living and interacting with each other in the same habitat or group of fossil species which are typically found together in the same habitat or site.
According to some ecologist biotic community is an association of a number of interrelated and independent populations belonging to different species, in a common environment which can survive in nature. Species is the sum of all the populations of same kind of organisms all over the world. Generally, a species is often defined as a group of organisms similar in structure, function and behaviours.
Biotic communities vary in size, and larger ones may contain smaller ones. Species interactions are evident in food or feeding relationships. A method of delineating biotic communities is to map the food network to identify which species feed upon which others and then determine the system boundary as the one that can be drawn through the fewest consumption links relative to the number of species within the boundary. Community of animals is called Zoocoenosis while plant community as Phytocoenosis. Microbiocoenosis is used for the microbial community.
Essay # 2. Characteristics of a Biotic Community:
In natural environment only one species cannot exist by them. Species always exist in a group of population that lives together in the same area. Population is the next level in ecological hierarchy. The word population has its origin in the Latin word ‘populus’ meaning ‘people’.
An association of a number of different interrelated populations of different species in a common environment in a nature forms a Biotic Community. Every biotic community needs abiotic factors for their survival. At any times the dominance of one abiotic factor determines the predominance of particular kind of population in a biotic community.
For example: A grass land biotic community has seed eating birds, mice and predatory birds living on small insects. A damp marsh has frogs, toads, fish, water insects and water birds that feed on small creatures. Aquatic plants of different kinds adapted for different intensities of light at the surface or at different depths would be present in a biotic community.
A group of individuals, having similar structural and functional characters, capable of potential interbreeding is termed as species. Several members of a species have definite habitat range where they find their food. In nature all species exhibit cooperative and competitive interactions among the members of the species (intraspecific) and also with members of other species (interspecific).
The members of a biotic community can be producers, consumers or decomposers. The members of a biotic community are all interdependent. A biotic community may be small or large. The pond community may occupy a limited area while the desert or grass land communities could spread over to miles.
A biotic community may consist of only plants or animals or sometimes includes both. As different species share a common environment, number of direct or indirect interactions exists between them inside a biotic community. A biotic community interacts with the abiotic factors and forms an ecosystem.
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A stable and self-sufficient community has certain specific characteristics:
(а) Dominance of Species:
Each community has one or more dominant species. These could be Pine, Oak, Sal or Teak depending on the area and climatic conditions in that biotic community. The dominant species are the most numerous plants. They are generally large in size and have the greatest biomass. They influence the local environment.
The species may be fewer in number in temperate forests 90% of trees may be pines and oaks of a biotic community. The species may be more in tropical rain forests. Andaman group of islands where there are about 12 dominant species.
(b) Habitat:
Biotic community occupies particular area with specific physical environment like temperature, humidity, soil, availability of water etc., which acts as a limiting factor and regulate the population size of various species within the community.
(c) Self-Sufficiency:
On the bases of nutrition, each community comprises autotrophic and heterotrophic as perfectly balanced. Plants are autotrophic and referred as producer; animals are heterotrophic organisms and referred as consumers. The remains and dead bodies of these producers and consumers are decomposed by the decomposers (bacteria and fungi) and help in the recycling of materials.
(d) Structure and Stratification:
A stable community comprises of various strata, each community consists of the population of particular kind of species. Their growth forms help to establishment the structure of a community and on their arrangement; community shows either horizontal layering called zonation or vertical layering called stratification.
(e) Species Diversity:
Community is formed of a number of different populations. The number of species and population abundance in a community also vary greatly. Species diversity depends upon size of the area, diversity of habitats in that area, temperature, humidity, availability of water soil type, altitude etc.
(f) Dominance and Succession:
Each community has different types of population only few species especially one of them is expressed in majority and called dominants. Each community develops as a result of a directional change called succession.
Essay # 3. Interaction among Biotic Community:
When various species (community) live together in a biotic community a numbers of interactions take place according to specific needs of food, shelter and habits.
There interactions have been observed as follows:
(i) Predation
(ii) Scavenging
(iii) Parasitism
(iv) Commensalism
(v) Symbiosis
(vi) Competition
(vii) Some Passive Interactions
(viii) Other Interactions
(i) Predation:
Predation is a direct and often complex interaction of two species in a biotic community. The stronger animal called predator that captures and feeds on the weak animal called prey. The decrease in number of predators leads to an increase in number of the prey.
An increase in the predator population leads to decrease in the prey population in a biotic community. These fluctuations play an important part in regulating natural population. Tiger feeds on deer, owls on rats etc. In a common biotic community an animal could be a predator as well as a preyat different times.
(ii) Scavenging:
Scavenging is a direct food relationship where animals feed on other dead animals called scavengers where as another animal in a biotic community, which either died naturally or have been killed. They play an important role in a biotic community as food is not wasted and also is disposed off. Vulture feeds on dead bodies. Hyenas and jackals feed on left over killed animals by lion. They may feed on big animals like zebra and giraffe killed by other animals.
(iii) Parasitism:
Parasitism is a negative interaction in a biotic community where one not only derives nourishment but also lives a part or the whole of life on another organism. The parasite is an organism that lives on another organism, the host from which it obtains food as well as shelter in a biotic community. It may be between animals between plants or between animals and plants in a biotic community.
In the host parasite relationship the weak attacks on the stronger. It is beneficial to parasite and harmful to host. Generally a parasite may cause an illness or disease but not kill the host except in few specific cases. There may be number of parasites on one host.
(iv) Commensalism:
In Commensalism one organism or a population is benefited while the other is neither benefited nor harmed. In some cases the host may be able to derive some minor benefit. There is no physiological exchange of any kind. The association may be temporary or permanent in a biotic community. Remora is a small fish attaches itself to the lower side of a shark. Remora feeds on scraps of shark’s food and is not harmed.
(v) Symbiosis:
Symbiosis is an association of two populations in a biotic community where both the populations are benefited. There is often a close or permanent association. In some cases both are so inter-dependent that neither can live alone in that biotic community. Lichens are the best example of symbiotic association.
(vi) Competition:
The two species in a biotic community interact in such a way that it affects their growth and survival. Both the species share the same resources like water, nutrients, space, sunlight, food, etc. of a biotic community. Members of both species compete to survive in that respective biotic community. There is a direct inhibition of one by another. There is no set pattern as anyone can succeed. Carnivorous animals like tiger and lion compete for the prey. Trees, herbs and shrubs compete for sunlight, water and nutrients in a biotic community.
(vii) Some Passive Interactions:
There are many interactions that exist in nature of a biotic community in between the animals, or between animals and the surrounding, which also help an organism to survive in that biotic community. The blending of an animal with its surrounding is called camouflaging. It is also known as protective coloration.
They camouflage their body shape and colour to suit the environment. Stick insect Carausius morosus resembles a thin dry branch. Dead Leaf butterfly Kalima parolecta resembles a dry leaf. Praying mantis Mantis religiosa resembles the green foliage. Mimicry is also a type of protective resemblance in a biotic community. In this an animal mimics another animal so as to avoid predation.
(viii) Other Interactions:
There may be many other interactions have been observed. The birds/animals are associated to bringing seed and fruit dispersal and pollination. The birds feed on ticks; they are parasites on the body of cattle. The Rufus woodpecker makes a nest in a hole in the ball shaped nest of the ants. The ferocious ants do not harm the eggs or young ones but the birds feed on these ants and keep a check on their population to continue their generation in a biotic community.
Essay # 4. Composition of Biotic Community:
Biotic communities consist of living as well as non-living component. Non-living organisms are called as abiotic and include water, sunlight, air etc. while living organisms are referred as biotic.
There are three types of living organisms inhabit a biotic community:
The classification of biotic organisms is as follows:
(i) Producers:
Producers or autotrophs include plants, algae and bacteria that survive via converting solar energy into food. These are mainly green plants. They synthesize organic food from simple inorganic compounds, namely carbon dioxide and water, with the help of chlorophyll and sunlight, hence the name as producer. The process is called photosynthesis.
It may be briefly represented as under:
6CO2 + 6 H2O→C6H12O6 + 6O2
The producers are very important for biotic community because they:
(i) Provide food and oxygen to the animals
(ii) Reduce CO2 and H2O contents from the environment.
Thus, they influence animals as well the environments.
(ii) Consumers:
Consumers or heterotrophs eat plants and animals to survive. These are mainly the animals. They are unable to synthesize food for themselves. Therefore, they take other organisms or their parts, hence their name. The consumers are called herbivores when they feed on plants and carnivores if they take other animals. Grasshopper, rat, rabbit, goat and cattle are common herbivores.
Frog, wolves, tiger and lions are familiar carnivores. Cat, dog, bear and man take both plant and animal food. They are termed omnivores. The consumers also use O2 of the environment and add to it CO2, nitrogenous waste matter and faeces. They, thus; also influence the environment as well as the organisms. Consumers include herbivores (known as primary consumers), which eat only plants, carnivores (known as secondary consumers), which eat other animals, and omnivores, which eat both plants and animals.
Subcategories of consumers are detrivores, or detritus feeders. These creatures eat plants and animals that are already dead. Their diet consists of dead organisms, as well as organic waste. Crabs, vultures and termites are well known example of detrivores, or detritus feeders.
(iii) Decomposers:
The final type of living organism is decomposers. They change plants that have died into nutrients that allow them to survive. Animals that live in the water or soil often feed off dead decomposers. These are mainly bacteria and fungi of decay. They are also named as reducers. They obtain food from the dead producers (plants) and consumers (animals) and latter’s waste products.
They decompose these materials into:
(i) Small organic molecules which they utilize themselves.
(ii) Inorganic compounds that are released into the environment for reuse as raw materials by the producers.
The decomposers not only return chemical nutrients to the environment, but also make space available for new producers. Without this, all life will ultimately cease to exit. Thus, the decomposers have a role in the environment. They are found in the soil, and the bottom of ponds, lakes and oceans.
Essay # 5. Biotic Stability:
A biotic community is a naturally occurring group of plants and animals living in the same environment. They all interact to make the community stable. It has been seen that more the number of species, more stable is the community. A biotic community containing a large population of Eucalyptus or any other plant may be totally wiped out by a fungal disease or insect infectation.
But if a biotic community contains many species and different kinds of plants, only one would wipe out at a time and the rest would survive. Since a biotic community is formed of a large number of diverse type of populations of plants and animals and microbes, all these populations are essential for biotic stability. Each species eats on a different kind of grass or shrubs. Some that feed on the same species while few feed at different stages of grass. This makes the biotic community rich and stable.
Essay # 6. Ecological Succession or Changes in a Biotic Community:
Ecological succession is the process of change in the species structure of an ecological community over time. The community begins with relatively few pioneering plants and develops through increasing complexity until it becomes stable community. It is a phenomenon or process by which an ecological community undergoes more or less orderly and predictable changes following disturbance or initial colonization of new habitat.
A community is built up over a period of time. As the time passes, communities change. In a biotic community there are interactions among the organisms and between the biotic and abiotic factors like climate, light, soil, etc. All these bring about changes in a biotic community.
A biotic community is a dynamic unit where tropic levels exist; there is a flow of energy and cycling of nutrients. It is a living part of an ecosystem. The wind, fire, volcanic activity or any other event in nature or man may destroy the organisms living in a biotic community.
Now if this area is left alone, a succession would start and ultimately a permanent biotic community would take shape. This process from the beginning to the climax may take thousands of years.
During this time there will be an orderly and progressive replacement of one biotic community by another till a relatively stable biotic community is established. This is called as ecological succession. A complete succession is called as Sere. A Sere is made up of a number of seral stages. A climax community is die final or the seral stage.
Ecological succession may be expressed as follows:
1. The species living in a particular place gradually change over time as does the physical and chemical environment within that area.
2. Succession takes place because through the processes of living, growing and reproducing, organisms interact with and affect the environment within an area, gradually changing it.
3. Each species is adapted to thrive and compete best against other species under a very specific set of environmental conditions. If these conditions change, then the existing species will be outcompeted by a different set of species which are better adapted to the new conditions.
4. The most often quoted examples of succession deal with plant succession. It is worth remembering that as plant community’s change, so will the associated micro-organism, and fungus and animal species. Succession involves the whole community, not just the plants.
5. Change in the plant species present in an area is one of the driving forces behind changes in animal species. This is because each plant species will have associated animal species which feed on it. The presence of these herbivore species will then dictate which particular carnivores are present.
6. The structure or ‘architecture’ of the plant communities will also influence the animal species which can live in the microhabitats provided by the plants.
7. Changes in plant species also alter the fungal species present because many fungi are associated with particular plants.
8. Succession is directional. Different stages in a particular habitat succession can usually be accurately predicted.
9. These stages, characterized by the presence of different communities, are known as ‘seres’.
10. Communities change gradually from one sere to another. The seres are not totally distinct from each other and one will tend to merge gradually into another, finally ending up with a ‘climax’ community.
11. Succession will not go any further than the climax community. This is the final stage.
“The developmental study of vegetation necessarily rests upon the assumption that the unit or climax formation is an organic entity. As an organism the formation arises, grows, matures, and dies… Furthermore, each climax formation is able to reproduce itself, repeating with essential fidelity its development.”
Causes of Plant Succession:
Climatic factors may be very important, but on a much longer time-scale than any other. Changes in temperature and rainfall patterns will promote changes in communities. As the climate warmed great successional changes took place. The tundra vegetation and bare glacial till deposits underwent succession to mixed deciduous forest.
The greenhouse effect resulting in increase in temperature is likely to bring community changes. Geological and climatic catastrophes such as volcanic eruptions, earthquakes, avalanches, meteors, floods, fires, and high wind also bring allogenic changes. Allogenic succession is caused by external environmental influences and not by the vegetation.
Soil changes due to erosion, leaching or the deposition of silt and clays can alter the nutrient content and water relationships in the ecosystems. Autogenic succession can be brought by changes in the soil caused by the organisms there. These changes include accumulation of organic matter in litter or humic layer, alteration of soil nutrients, change in pH of soil by plants growing there.
The structure of the plants themselves can also alter the community. When larger species like trees mature, they produce shade on to the developing forest floor that tends to exclude light-requiring species. Animals also play an important role in allogenic changes as they are pollinators, seed dispersers and herbivores. They can also increase nutrient content of the soil in certain areas creating patches in the habitat. This may create regeneration sites that favor certain species.
Mechanisms of Succession:
Frederic Clements in 1916, proposed the theory of ecological succession. According to this theory succession had a powerful influence on ecological community. Clements’ concept is usually termed classical ecological theory.
According to Clements, succession is a process involving several phases:
(i) Nudation:
It is the development of a bare site uninhabited by any organisms. The process is usually caused by disturbances Succession begins with the development of a bare site, called Nudation. These factors can be either topographic like soil erosion, wind action etc., climatic like hails, storm, glaciations, fire etc.; or biotic. The area thus formed can sustain only autotrophic organisms which can utilize inorganic substrates. The environmental conditions are set up for the inhabitation of new species.
(ii) Migration:
The process of migration helps the arrival of seeds, spores or other reproductive propagules for establishment of species. The other species are non-native organisms which can spread widely in a community. These are usually threatening the normal ecosystem and causative agents for community disturbance.
However, in succession process, they help to alter the soil texture and function. R-selected species are often the first colonizers due to their high reproductive rates and better dispersal mechanisms.
(iii) Ecesis:
This is the initial establishment of plant community. It involves establishment and initial growth of vegetation. This is dependent on the soil structure. The stage is also called as ‘colonization’. In this stage, the early colonizing species proliferate abundantly through germination, growth, and reproduction.
Ecesis is due to allogenic mechanisms. This is the stage at which the pioneer species survive through the dispersal mechanisms. The different pioneer species can have different maturation rates which allow this process to be longer and gradually allowing replacement of some species by others. The process also makes the soil structure suitable for those species.
(iv) Competition:
Once the few initial species have become established the intra as well as interspecific competition among the species starts. As vegetation became well established, grew, and spread; various species began to compete for space, light and nutrients.
This stage is called competition. The competition is usually for resources such as food, water etc. Competition is found in both plants as well as animal species. The process leads to sharing of resources (resource partitioning) or competitive exclusion.
(v) Reaction:
The environmental conditions get modified by the action of species occupying the habitat. These changes subsequently trigger the displacement and replacement of one species by another. During this phase autogenic changes affect the habitat resulting in replacement of one plant community by another.
The existing community will be unable to support itself due to the harsh conditions. The major underlying mechanism is autogenic succession in which the plants themselves alter the environmental conditions.
(vi) Stabilization:
Stabilization is the process by which the climax community gets established. A climax community is mature, self-sustaining, and stable and is the final stage of succession. The physical and chemical conditions are altered and stabilized to such levels that it supports the entire community.
The climax communities are best adapted to the regions of succession and the community structure is likely to continue until another disturbance steps in. This represents a steady state of ecological equilibrium with specific composition, structure and energy flow. Reaction phase leads to development of a climax community.
(vii) Aggregation:
Aggregation is the increase in population of the species which has become established in the area. The shrubs replace the small herbs in most successions. This also proves as a source of food for future inhabitants
Hydrosere:
Hydrosere is the primary succession sequence which develops in aquatic environments such as lakes and ponds. It results in conversion of water body and its community into a land community. A hydrosere is a plant succession which occurs in an area of fresh water. Hydrosere is simply a succession which starts in water. Hydrosere, also called hydrarch involves the ecological succession in the newly formed pond or lake.
A wetland is a transitional area. Freshwater provides a good and an excellent place to observe several stages of a hydrosere at the same time. In time, an area of open freshwater such as a lake will naturally dry out, ultimately becoming woodland.
During this process, a range of different habitats such as swamp and marsh will succeed each other. This succession from open water to climax woodland is likely to take at least two hundred or more years. Some intermediate stages will last a shorter time than others.
Fresh Water:
Fresh water lack soil, minerals etc., which support the growth of vegetation. Deep freshwater will not support rooted, submerged plants because there is not enough light for photosynthesis in the depths. There will be micro-organisms and plankton floating in the water.
Ecological succession is of great importance as:
(i) It provides information, which help to have control on the growth rate of one or more species in a given geographical area.
(ii) It helps in reforestation and forest management programs
Xerosere/ Lithosere:
A xerosere may include lithoseres (on rock) and psammoseres (on sand). A lithosere is a sere (succession) on rock. Lithosere is a plant succession starts on a newly exposed rock surface. Xerosere is a plant succession which is limited by water availability. It includes the different stages in a xerarch succession. Xerarch succession of ecological communities originated in extremely dry situation such as sand deserts, sand dunes, salt deserts, rock deserts etc.
Pioneer species are the first organisms that colonies an area, of which lithoseres are an example. They will typically be very hard i.e., they will be xerophytes, wind-resistant or cold-resistant. In the case of a lithosere the pioneer species will be lichens, cyanobacteria and algae, which create their own food and water.
They are autotrophic and so do not require any external nutrition except sunlight. Other examples of lithoseres include communities of mosses and lichens, as they are extremely resilient and are capable of surviving in areas without soil. Xerosere or lithosere is a gradual change in community due to change in climate, nutrition etc.
Key points of Lithosere /Xerosere:
(i) Bare rock colonized, by pioneer community, for example, lichens, mosses, bacteria, that can survive in hardy conditions, and need few nutrients.
(ii) Rock slowly weathered creating thin soil.
(iii) Plants die, creating humus, leading to a more fertile soil; grasses replace the mosses and lichens as the dominant species.
(iv) Grasses decrease in number; quick-growing shrubs become dominant.
(v) Fast growing trees dominate.
(vi) Over time slower growing trees such as oak become dominant and form the climatic climax community.