Class 12 Biology Organisms and Populations Competition


Competition is struggling by the organisms for the same resources like food, shelter and sex.

The competition is between two organisms belonging to same species, this is called intraspecific competition.

The competition between organisms belonging to different species is called interspecific competition. For example- in some shallow South American lakes visiting flamingoes and resident fishes compete for their common food, the zooplankton in the lake.

Fig. flamingoes  

Resources need not be limiting for competition to occur. For example- Abingdon tortoise in Galapagos Islands became extinct within a decade after goats were introduced on the island, apparently due to the greater browsing efficiency of the goats.

Fig. Abingdon tortoise

The occurrence of competition in nature comes from competitive release.

Competitive release is the process in which a species whose distribution is restricted to a small geographical area because of the presence of a competitively superior species, is found to expand its distributional range dramatically when the competing species is experimentally removed.

Connell’s elegant field experiments showed that on the rocky sea coasts of Scotland, the larger and competitively superior barnacle Balanus dominates the intertidal area, and excludes the smaller barnacle Chathamalus from that zone.

Gause’s ‘Competitive Exclusion Principle’ states that two closely related species competing for the same resources cannot co-exist indefinitely and the competitively inferior one will be eliminated eventually

Species facing competition might evolve mechanisms like resource partitioning that promote co-existence rather than exclusion.

If two species compete for the same resource, they could avoid competition by choosing different times for feeding or different foraging patterns, this is called resource partitioning.

MacArthur showed that five closely related species of warblers living on the same tree were able to avoid competition and co-exist due to behavioural differences in their foraging activities.

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