Biotic factors and abiotic factors are two types of factors that have an influence on ecosystem. Biotic factors are the living factors that have an influence on ecosystem. Organisms do not exist alone in nature but in a matrix of other organisms of many species. Many species in an area will be unaffected by the presence or absence of one another, but in some kisses two or more species will interact. The evidence for such interaction is quite direct populations of one species are different in the absence and in the presence of a second species.


  1. AUTOTROPHS: Make there own food . They are the producers. Example- plants
  2. HETEROTROPHS: Feed on other organisms .  Example- Animals, fungi, bacteria
    1. Consumers: herbivores, carnivores, omnivores, Detritivores.

Herbivores: Animals that get it’s energy from eating plants and only plants. Example- cow, elephant

Carnivores: Meat eaters, example: cats, lion, tiger, dogs, etc.

Omnivores: Feed on both plants and animals . Example- human, Raccoons etc.

Detritivores: heterotrophic organisms who ingest dead organic matter. Examples- earthworms, woodlice, etc.

B. Decomposers: Decompose the remains of organism. Example: bacteria and fungi.


Fig: Interspecific interaction between flower and tree.

Intra specific interaction can be positive or negative.

The types of interactions are:

  1. Positive interaction
    1. Mutualism
    1. Commensalism
    1. Protocooperation
  2. Negative interaction


            (i) Social parasitism

            (ii) Parasitism

            (iii) Predation

  3. Ammensalism

  4. Competition


In such type of interaction both the species are benefited by each other. This benefit can be food, shelter, substratum or transport.


In mutualism both the species are strongly benefited. This type of positive interaction is obligatory positive interspecificinteraction.Previously it was termed symbiosis. In this type of interaction, both the species derive benefit and their exist a close and often permanent and obligatory contact. Which is very important for each other’s survival. It result in co-evolution.

  1. Pollination by animals : Some insects such as bees, moths, butterflies, etc., and birds take food from the nectar , pollens or other plant products, and in return bring about cross pollination.
    • Dispersal of fruits and seeds by birds and mammals
    • Mutual defense in ants and acacias: The acacias have large, hollow thorns in which ants live. The ants feed on modified leaflet tips. Which are primary source of protein and oil for the ants, and also on enlarged nectaries which supply sugars. The acacia ants continually patrol the leaves and branches of the tree.
    • Lichens: Symbiotic relationship between fungus and algae.
    • Symbiotic nitrogen fixation: Here a bacterium Rhizobium forms nodules in the roots of legumes plants and lives symbiotically with the host. Bacteria get a protective space to live in and derive prepared food from the roots of higher plants and in return fix gaseous nitrogen.
    • Few more examples are Mycorrhizae, Zoochlorellae and zooxanthellae, microorganisms and cellulose digestion etc. 

In Commensalism two or more species are associated and at least one specie is benefited from it. Some common examples of commensalism are the following :

  • Lianas: These plants are common in tropical rain forests where light at ground level is scarce because of the dense and multi-storeyed growth of vegetation.Lianas are vascular (woody)plants rooted in the ground but which climb up with the supportof other trees and reach almost to the top of the forest canopy.
    • Epiphytes:  Epiphytes are the plants growing on other plants. They use other plants only as support and not for water or food supply. Epiphytes differ from the lianas in that they are not rooted into the soil. They may grow on trees, shrubs or larger submerged plants. They grow either on the trunks or leaves.Certain common examples of epiphytes are orchids, bromeliads, hanging “mosses, Usnea and Alectoria.
    • Epizoans. Some plants grow on the surfaces of animals. For example, some green algae grow on the long, grooved hair of sloth. Basicladia (Cladophoraceae) grows on the backs of fresh wate turtle.
    • Epizoite. Likewise, ectocommensals or epizoite animals are associated with another animal for the purpose of anchorage and protection. Many small animals, for example, become attached to the outside of larger ones, such as the protozoans Trichodina and Kerona on Hydra.
    • Commensals may also be internal: For example,many harmless protozoans occur in the intestinal tract ofmammals, including man. Some microorganisms such as bacterium Escherchia coli is found in human colon.


In case of negative interactions, one or both species are harmed in any way during their life period. These types of interactions were called as antagonism. The negative interactions include the following three broad categories:

  1. EXPLOITATION . In exploitation, one species harm the other by making its direct or indirect use for support, shelter or food. It is of following types:
    1. Social parasitism: Social parasitism describes the exploitation of one species by another, for various advantages. It is a kind of parasitism in which the parasite foists the rearing of its young into the host. Social parasitism in various stages of development is found among some higher vertebrates and insects. For example, there occurs an egg parasitism in two species of birds-old world cuckoos and the brown headed cowbirds of North America, both of which do not build nests of their own, rather they deposit their eggs in nests of other species, abandoning eggs and young to the care of foster parents.
    1. Parasitism: Parasitism is a kind of harmful coaction (disoperation) between two species. It is the relation between two individuals wherein one individual called parasite receives benefit at the expense of other individual called host.The parasites may be viral parasites (e.g. bacterial., plant and animal viruses), microbial parasites (e.g., bacteria, protozoa, fungi, etc.), phytoparasites (e.g., plant parasites).
    1. Predation. Predation occurs when members of one species eat those of another species. Often, but not always, this involves the killing of the prey. Most of the predatory organisms are animals, but there are some plants (carnivores) also.For example, Peale’s falcon shows a marked preference for ducks and pheasants. Deer exhibits a pronounced preference for certain species of browse. Carnivorous fungi.:A number of fungi such as species of Dactylella, Dactylaria, ArthrobotrysZoophagus, etc., capture insects, nematodes and other worm-like animals. Such fungi use specialized structures such as traps on snares which are formed on their mycelia to capture the nematodes.


Amensalism is a situation in which one population definitely inhibits the other species while remaining unaffected itself. Example: Penicillium, a fungus found in soil produces antibiotics such as penicillin, have been used extensively in human medicine.


The presence of other organisms may limit the distribution of some species through competition. Such competition can occur between any two species that use the same sorts of places. For example- Birds, rodents and ants may compete for seeds in desert environments.

There are different types of competition:

  1. Resource competition, 2. Interference competition (Intraspecific or Interspecific competition).

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