General Ecology, Biology tutorial


A community is build up of populations of various organisms living altogether in a unit environment. It is the way in which these organisms relate in general for survival and sustenance from producers to different levels of consumers.

Definition of Ecosystem:

Ecosystem is a word employed to signify a whole community of organisms and its atmosphere as a unit. In another words, it comprises of the community of organisms (that is, biotic factors) plus the related physical environment (that is, abiotic factors). It is generally self sufficient and can be temporary or permanent.

Components of ecosystem:

The structure of ecosystem gives information regarding the range of climatic conditions which prevail in the area. From the structural view-point all the ecosystems comprise of the given four fundamental components:

Abiotic Components:

The abiotic components of the ecosystem are all of the non-living elements. They comprise the water, air, temperature and the rocks and minerals which structure the soil.


Producers are the living organisms in the ecosystem which take in energy from sunlight and utilize it to convert carbon-dioxide and oxygen to the sugars. Plants, algae and photosynthetic bacteria are all illustrations of producers.


Consumers are the living organisms in the ecosystem which get their energy from consuming the other organisms. Theoretically, consumers are further categorized by what they eat: Herbivores eat producers, carnivores eat other animals and omnivores eat both. All along with producers and decomposers, consumers are part of what is known as food-chains and webs, where energy and nutrient move can be mapped out.


Decomposers are the living component of the ecosystem which breaks down waste material and dead organisms. Illustrations of decomposers comprise earthworms, dung beetles and various species of bacteria and fungi.

Types of Ecosystems:

Ecosystems can be categorized into Terrestrial Ecosystems and Aquatic Ecosystems.

Terrestrial Ecosystems:

An ecosystem is a group or collection of communities of both living and non-living things which are interconnected. While numerous ecosystems exist on land and in the waters of the world, terrestrial ecosystems are those which are found only on land. The biotic or living things found in an ecosystem, comprise different life forms like animals and plants. The abiotic, or non-living things found in the ecosystem, comprise the different land-forms and the climate.

While there have been numerous categorization schemes developed over time, it is now usually accepted that there are six kinds of terrestrial ecosystems. These comprise tundra, taiga, deciduous forest, grass-lands, tropical rain forests and deserts.

Aquatic Ecosystems:

Aquatic ecosystems are mainly found in marine habitats, brackish estuaries, streams, rivers, lakes and ponds. The producers here are represented through phytoplankton (that is, drifting organisms) such as algae. Primary consumers in aquatic ecosystems comprise annelids, molluscs and aquatic arthropods.

The secondary consumers (that is, primary carnivores) are aquatic birds and fish. Similar to in the terrestrial ecosystem these might in turn fall prey to the secondary carnivores and other phases of predation might take place

Habitats and Niches:

In an ecosystem, the habitat is employed to explain the environment or range of environments where the organism lives. It is a natural place of growth or occurrence of a species. A few species encompass definite habitat, for instance the lowland gorilla (Gorilla gorilla) consists of as its habitat low land tropical secondary forests whereas the mangrove plant's habitat is mangrove swamps. However some other species have some habitats. A good illustration is the tiger (that is, Panthera Tigris) whose habitats comprise tropical rain forest, snow-covered coniferous and deciduous forests and mangrove swamps.

Smaller organisms that live in very restricted regions such as on a specific plant or animal or in a specific area of the soil have where they live more specifically explained as microhabitat. We can therefore encompass a microhabitat for fleas or lice.


Dissimilar to the habitat where an organism is found, the niche is a complete explanation of how the organism associates to its physical and biological atmosphere. That is, the role of an organism in a community, its behavior and the manner in which the behavior changes at various seasons and different times of the day. It can be observed as a method of 'making' a living in each functional category in the operation of the ecosystem. The factors which make up an organism's niche find out whether it can exist in a given ecosystem and as well with how many species it can exist altogether.

A niche can either be a realized niche if the organism is competing with others in an ecosystem or a basic niche which is the niche an organism occupies when competitors were not present. Beneath a competing situation it has been realized that no two species of organisms occupy the similar niche therefore supporting the idea of competitive exclusion. One species will displace the other which might find the other niche or go to extinction.

The concept of food chain:

Green plants, the primary producers in an ecosystem imprison energy from sunlight which fall on their leaves and transform it to food energy. When such plants are consumed by other organisms, a percentage of the plant's accumulated energy is really transformed into the bodies of the organisms which consume them. Some levels might be recognized among such consumers. The herbivores (that is, primary consumers) feed directly on the green plants and serve up as food for the primary carnivores (that is, secondary consumers). These in turn might fall prey to secondary carnivore and in certain cases other phases of the nutritional dependency. The tissues of different animals and plants in the community might also be eaten by parasites and after the organisms are dead, by scavengers and saprophytes of numerous sorts.

The organisms (animals and plants) from each of these levels feeding on one other make up a food chain. Simply stating, it explains a one line eating relationships between species in an ecosystem.

 Food Web:

In real life, it is instead rare for a given type of organism to feed on only one type of organism. Generally, each will feed on two or more other types and in turn will be fed on by some other types of organisms. Whenever diagrammed, the relationship appears as a sequence of branching lines instead of as one straight line. This is termed as a food web. This is really a set of interconnected food chains through which energy and materials circulate in an ecosystem.

Trophic levels and pyramidal relations:

Each and every successive level of nourishment as presented by the links of the food chain is termed as a Tropical Level. It exhibits what organisms feed on and what feeds on them. The plant producers in an ecosystem comprise the first tropic level, the herbivores form the second and the primary carnivores form the third level and so forth.

For illustration, the guava plant is the first Trophic level, the hare the second, the hyena third and the lion fourth. Pyramidal relations might be found among the organisms at various Trophic levels in the ecosystem.

Pyramid of numbers:

Among the animals of a community, the herbivores are in general the most abundant. They take in food materials synthesized by the plant producers and pass it on to the succeeding consumers. Primary carnivores which prey on the herbivores is less plentiful and secondary and tertiary carnivores usually exist in still fewer numbers. These numerical associations having the more rich species close to the base of the food chain and the less plentiful species close to the top is termed as the pyramid of numbers. The existence of parasites often leads to the inverted pyramid of numbers when lots of parasites much smaller are joined to the host.

Pyramid of biomass:

The size growth rate and long life of species making up a specific ecosystem are such that the living weight or biomass of the members of the food-chain presents at any one time form a kind of pyramid. In a land biotope, the biomass of the vegetation existing at the moment of observation is generally the greatest and the biomass of herbivores carnivores and further links in the food-chain are gradually smaller.

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