Interactions among species is divided into two categories:

  1. Intraspecific: It is type of interaction that occurs between populations of same species. Example: Social, family, cannibalism etc.
  2. Interspecific: It is type of interaction that occurs between population of different species. Example: Parasitism, Predation, Mutualism etc.


Interspecific Interactions

The interactions are usually indicated in ‘+, -, 0’ form regarding both partners as following:

Plus sign ‘+’ indicating benefit.

Minus sign ‘-’ indicating harm/inhibition.

Zero ‘0’ indicating neither benefit nor harm i.e. neutral.

S. No.Type Of Species InteractionSpecies ASpecies B

1) Neutralism: (0, 0)

  • When populations of two species coexist in an ecosystem with neither affecting the other.
  • Example: In desert, Cactus & Tarantulas co-exist with no or insignificant interaction.

2) Commensalism: (+, 0)

  • When one species population is benefitted (commensal) while other remains unaffected (host).
  • ‘Commensal’ means ‘eating at same table’.
  • Types of commensalism:
    • Phoresis: (Phoresis = to carry)
      • The phoront is carried in/on by the host from one place to another.
      • Purpose is transportation/dispersal. No metabolic/feeding interaction occurs in between them.
      • It can be facultative or obligatory.
      • Example: Pseudoscorpion (Cordylochernes scorpioides)is usually found under the elytra of harlequin beetle (Acrocinus longimanus).
    • Inquilism: (Inquilism = tenancy)
      • Inquiline lives as commensal in nest, burrow or dwelling place of the host.
      • Example: Habrotrocha rosa lives in pitcher of Sarracenia purpurea (Purple pitcher plant).
    • Metabiosis:
      • One organism creates suitable environment for living of other organism.
      • Example: Hermit crabs live in the shell of gastropod to protect their body.

3) Protocooperation: (+, +)

  • Populations of both species are benefitted by the interaction.
  • Interaction is not obligatory.
  • Also called facultative cooperation or facultative mutualism.
  • Example: Sea anemone (Adamsia palliata) attached to shells of hermit crab (Eupagurus prideauxi).

4) Mutualism: (+, +)

  • Populations of both the species are benefitted.
  • Interaction is obligatory i.e. neither can survive without the other under natural conditions.
  • Example: Lichens

5) Amensalism: (0, -)

  • One species population is inhibited but other remains unaffected i.e. this interaction is detrimental to one while other is not affected.
  • Example: Release of certain toxins by one plant species inhibits growth of the other.

6) Parasitism: (+, -)

  • Parasitism is a type of interspecific relationship in which one organism (parasite) is metabolically dependent on the other (host).
  • The parasite benefits at the expense of the host and is also usually smaller in size than its host.
  • Parasitic relationship is said to obligatory as normally the parasite cannot survive without its host
  • Example: Ticks & Leeches are blood sucking parasites.

7) Predation: (+, – )

  • Type of interspecific interaction in which one organism (predator) obtains food energy by consuming the other organism (prey), usually after killing it.
  • Predation also includes grazing by herbivores.
  • In contrast to parasitism, predator is usually larger than prey & prey is killed by the predator for food.
  • Example: Lion kills a zebra & consume it.

8) Competition: (-, -)

  • Interspecific competition – Interaction between populations of different species at same trophic level, which adversely affects one/some or all the interacting species. Example: Lion & Tiger compete for same deer for food. [Intraspecific Competition discussed under Intraspecific Interactions]


(Symbiosis = living together)

  • It is a type of close or intimate relationship among organisms of different species.
  • Members of symbiotic relationship are called symbionts.
  • Commensalism, Parasitism & Mutualism are considered symbiotic relationships.

To be continued…

Harjeet Kaur

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