Organisms and Populations — BIOLOGY STD 12 Science — Question

→ It is a process in which fitness of one species ('r'value) is significantly lower in presence of another species.
→ Interspecific competition is a potent force in organic evolution.
→ Competition occurs when closely related species compete for the same limited resources.
→ Unrelated species can also compete for the resource. E.g. Flamingoes & fishes in some shallow South American lakes compete for zooplankton.
→ Competition occurs in abundant resources also. E.g. In interference competition, the feeding efficiency of one species is reduced due to the interfering and inhibitory presence of other species, even if resources are abundant.
Evidences for competition :
→ The Abingdon tortoise in Galapagos Islands became extinct within a decade after goats were introduced on the island, due to greater browsing efficiency of the goats.
→ Competitive release : It is the expansion of distributional range of a species when the competing species is removed.
→ Connell's field experiments : On the rocky sea coasts of Scotland, there are 2 barnacle species: Balanus (lager & competitively superior) & Chthamalus (smaller). Balanus dominates intertidal area and excludes Chthamalus. When Connell experimentally removed Balanus, Chthamalus colonized the intertidal zone.
→ Gause's 'Competitive Exclusion Principle' :
→ It states that two closely related species competing for the same resources cannot co- exist indefinitely and the competitively inferior one will be eliminated eventually. This may be true in limited resources, but not otherwise.
→ Species facing competition may evolve mechanisms for co-existence rather than exclusion. E.g. resource partitioning.
→ Resource partitioning : It is the division of limited resources by species to avoid competition. For this, they choose different feeding times or different foraging patterns. E.g. MacArthur showed that five closely related species of warblers living on a tree could avoid competition and co-exist due to behavioural differences in their foraging activities.