After all, it must take into account the life habits of over two million different kinds of animals and plants and it considers all manner of influence and interactions among them. Fortunately, however, the innumerable facts of ecology can be distilled into following some relatively basic and simple principles:
The ecology is the study of ecosystems or the totality of the reciprocal interactions between living organisms and their environment. The term organism refers to an individual unit constituted to carry on the activities of life.
It is a dynamic biological unit which is greatly influenced by an enveloping and fluctuating environment. For a given organism, the environment includes all the surrounding physical and biological factors, with which it interacts.
The factor is any external force, substance, or condition that affects organisms in any way. Thus, environment is sum total of everything that directly influences the animals chances of survival reproduction (Maelzer, 1965).
The intimately local and immediate surroundings of the organism is called microenvironment, while, the sum total of the physical and the biotic conditions existing external to the organism and its microenvironment.
The total life-containing and life-supporting environment of the world is restricted to a very thin and irregular veil or film around the globe this thin veil of living material of earth is called ecosphere or biosphere.
Thus, the biosphere is that part of the earth in which life exists (Hutchinson, 1970). The biosphere too is not entirely hospitable to life, in one region called apiaries here; severe environmental conditions permit inhabitation by some organisms only in the resistant stages of their life-cycles.
The parabiosphere includes such broad areas as the higher altitudes, the Polar Regions, the deepest ocean troughs, the most extreme deserts; and such localized regions as volcanoes, geysers, and grossly-polluted areas of land and water.
The remaining portion of biosphere is called enbiosphere, in which active metabolic processes of organisms are possible. Besides the biosphere, the three other main compartments of the world are air (atmosphere), water (hydrosphere), and earth or laud (lithosphere).
The entire world can be considered as a single vast ecosystem of the universe as its biotic or living part is build by the biosphere (organisms) and its abiotic or non-living portion is formed by atmosphere, hydrosphere, and lithosphere.
The ecosystem is any spatial or organizational unit which includes living organisms and non-living substances interacting to produce an exchange of materials between the living and non-living parts.
The ecosystem can be studied from either structural or functional aspects. The structural aspects include a description of the arrangement, types and numbers of species and their life histories, along with a description of the physical features of the environment. The functional aspects of the ecosystem include the flow of energy and the cycling of nutrients.
The non-living part of the ecosystem includes different kinds of habitats such as air, water and land, and a variety of abiotic factors. Habitat is the natural abode or locality of an animal, plant or person.
It includes all features of the environment in a given locality. For instance, water is used as habitat by aquatic organisms and it comprises three major categories—marine, brackish and freshwater habitats.
Each of these may be subdivided into smaller units, such as freshwater habitat may exist as a large lake, a pond, a puddle, a river or a stream. Similarly, the land is used as a habitat for numerous terrestrial organisms. It includes many major categories of landmass’s which are called biomes.
Biomes are distinct large areas of earth with relatively homogeneous climatic factors and flora and fauna, e.g., deserts, prairie, tropical forest, etc. Soil is also used as a habitat by a variety of microbes, plants and animals.
Among the main abiotic factors of the ecosystem are such climatic factors as solar radiation, temperature, wind, water currents, rainfall, and such physical factors as light, fire, pressure, geomagnetism, and such chemical factors as acidity, salinity and the availability of inorganic nutrients needed by plants.
The biological (biotic) factors of ecosystem include all the living organisms—plants animals bacteria and viruses. Each kind of living organism found in an ecosystem is called a species. A species includes individuals which are genetically alike and which are capable of freely inter-breeding and producing fertile offspring’s.
In an ecosystem, there exist various relationships between species. Two species may have a negative effect upon one another (competition), a neutral effect (neutralism) or a beneficial effect (protocooperation and mutualism).
Other relationships occur in which one species benefits and the other is harmed (predator-prey, herbivore-plant, parasite-host), or where one benefits but does not affect the other (commensalism), or where one species is harmed by any other species that derives no benefit (amensalism). Likewise, species may aggregate, or separate, or show a random relationship to one another.
The distribution and growth of plants and animals in an ecosystem are controlled by both abiotic and biotic features of the environment. Any factor acting to alter the growth and survival of a population is called a limiting factor.
A population is a group of inter-acting individuals, usually of the same species, in a definable space. Thus, one can speak of population of deer on an island, the population of locusts in a crop-field, and the population of fishes in a pond.
The size of a population of any given species is determined by a balance between its reproductive potential and the environmental” resistance thus, population size is determined by the relative number of organisms added to or removed from the group. Recruitment into the population is a function of birth rate and immigration rate. Loss from the population is a function of death rate and emigration.
Population regulation is achieved by following factors—physical attributes of the environment (e.g., climate), Food (quantity and quality), disease (host-parasite relationships), predation and competition (inter-specific and intra-specific).
An ecosystem usually contains numerous populations of different species of plants, animals and microbes, all interacting with one another as a community and with the physical environment as well a community or biotic community, thus, consists of the populations of plants and animals living together in a given place. For example one refers to the community of an oak forest, grassland, a coral reef, a desert or a pond.
Further, each organism in a community has a distinct ecological niche; different species tend to live in different habitats, eat different foods and live with different life-styles.
The ecological niche, thus, is a more inclusive term that includes not only the physical space occupied by an organism, but also its functional role in the community (e.g., its trophic position) and its position in environmental gradients of temperature, moisture, pH, soil and other conditions of existence.
Further, all biological communities exhibit some form of layering or stratification, which largely reflects the life forms of the plants and which influences the nature and distribution of animal life in the community.
From the energetic viewpoint, the ecosystem may be divided into three types of organisms: producers, consumers, and reducers.
Photosynthetic algae, plants and bacteria are the producers of the ecosystem; all other organisms depend upon them directly or indirectly for food. Consumers are herbivorous, carnivorous, and omnivorous animals; they eat the organic matter produced by other organisms.
Reducers are heterotrophic organisms like animals; they are fungi and bacteria that decompose dead organic matter. Thus the ecosystem is composed of organisms eaten by, or eating other organisms.
Species are related by their feeding behaviour in food chains or food webs. There are two basic types of food chains: the consumer food chain includes the sequence of energy flow from producer > herbivore > carnivore > reducer; the detritus food chain bypasses the consumers, going from producer > reducer.
Further, it is found that approximately 30 natural elements are essential to organisms; these are cycled through the abiotic compartments of world, i.e., atmosphere, hydrosphere, and lithosphere as well as the producers, consumers, and decomposers of the biological community (biosphere).
Organisms take in inorganic nutrients (e.g., carbon, oxygen, hydrogen, sodium, nitrogen, phosphorus, calcium, sodium, sulphur, potassium, chlorine, etc.) from the soil, water, and air; they eliminate their wastes, and their bodies are rendered into inorganic molecules once again.
Thus, water and minerals shuttle among the air, land, and water with an occasional pause in an organism. Such cycling of nutrients in circular paths in between biotic and abiotic components of the ecosystem are called biogeo- chemical cycles.
Moreover, changes occur within ecosystems. The most dramatic are those associated with succession. Ecological succession is a sequential change of organisms as an area progresses from a condition in which it is relatively poor in species composition and organic content, until it becomes a diverse and rich biological community.
Primary succession begins on rock, sand, or mud where little or no organic material has been previously present. Secondary succession begins where organic matter been present, such as a burned out forest region, or a bulldoze red landscape. The final stage in succession is called climax.
It is predictable for a given area and depends upon rainfall, temperature and soil conditions. Even within stable ecosystems, species and their activities vary in time and space. Recurrent daily and seasonal rhythms exist in the lives of all organisms.
These are driven by environmental changes or by internal “biological clocks”. A biological clock is a hypothetical internal mechanism by which an organism can keep track of time and govern its activities.
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