Population Interactions – Competition


Competition is the struggle between two or more organisms of same or different species for available resources.

Intraspecific competition is competition between individuals of same species. It is more acute as the requirements are same and can reduce the size of the population.

Interspecific competition is competition between individuals of different species. It occurs when organisms of different species have similar feeding habits. They belong to the same trophic level.

  • E.g., In grassland, there is competition between herbivores like rabbit, deer, bison.
  • Competition between resident fishes and visiting flamingoes for the zooplankton in the lake.
  • Carnivores like tiger and leopard compete for the same prey.
  • In forests trees, shrubs and herbs compete for water, minerals, and sunlight.

In interspecific competition, where resources are abundant, interference is seen. The feeding efficiency of one species might be reduced due to the interference & inhibitory presence of another species.

When resources are limited competition leads to the elimination of inferior species. e.g., Introduction of goats in Galapagos islands made Abingdon tortoise extinct due to greater browsing efficiency of goats.

Competitive release:

It is a dramatic increase in the population of a less distributed species in a geographical area when its superior competitor is removed from the area.

e.g., Connell’s experiment showed that competition between the superior barnacle Balanus and the smaller barnacle Chathamalus in the intertidal area of the rocky seacoast of Scotland eliminates the smaller species from the region.

GAUSE’s ‘Competitive Exclusion Principle’:

Two closely related species competing for the same resources cannot coexist indefinitely and the inferior one will be eliminated eventually.

His experiment was by using two different species of Paramecium.

Only when resources are limited a species is eliminated.

Resource partitioning:

  • Species facing competition might evolve mechanisms so that it can coexist by ‘resource partitioning’–if two species are competing for the same resource, they can avoid competition by choosing different times for feeding or different foraging patterns.
  • MacArthur showed that five closely related species of warblers lived on the same tree by behavioral differences in their foraging.

Plants and herbivores are more affected by competition than carnivores.



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