Equilibrium theory of island biogeography -
Discovered by Robert Mcarthur and E.O. Wilson in 1967
This theory is based on species are relationship ,Species isolation relationship and species turn over .
Acc. to this theory the number of species inhabiting an island is based on the dynamic equilibrium between the immigration of new species and extinction of species previously established .
So ,in simple words it would be the number of species in an island reflects the balance between the rate at which new species colonize it and the rate at which the populations of established species become extinct .The island will reach equilibrium when extinction rates equal immigration rates.
NOTE -The thoery explains about the patterns of species richness in island . It also explains the reason of lower number of species in an island .Over time, the countervailing forces of extinction and immigration result in an equilibrium level of species richness.
To understand their theory, take a look at the graph . The axis on the bottom of the graph is the number of species. If we follow the blue line, it shows that as the number of species increases, the rate of immigration begins to decrease. That's because as more and more species arrive, the chances grow that that species is already present.
Closer islands will have more species on them than far islands, just because closer islands are easier to reach. Extinction is lower on islands close to the mainland because of the likelihood of immigration. There is more of a chance that new immigrants will arrive and keep a species in existence on that island.
Rates of immigration to an island are mainly determined by the distance from the mainland to the island, and rates of extinction on the island are mainly determined by island size.
Discovered by Robert Mcarthur and E.O. Wilson in 1967
This theory is based on species are relationship ,Species isolation relationship and species turn over .
Acc. to this theory the number of species inhabiting an island is based on the dynamic equilibrium between the immigration of new species and extinction of species previously established .
So ,in simple words it would be the number of species in an island reflects the balance between the rate at which new species colonize it and the rate at which the populations of established species become extinct .The island will reach equilibrium when extinction rates equal immigration rates.
NOTE -The thoery explains about the patterns of species richness in island . It also explains the reason of lower number of species in an island .Over time, the countervailing forces of extinction and immigration result in an equilibrium level of species richness.
To understand their theory, take a look at the graph . The axis on the bottom of the graph is the number of species. If we follow the blue line, it shows that as the number of species increases, the rate of immigration begins to decrease. That's because as more and more species arrive, the chances grow that that species is already present.
Closer islands will have more species on them than far islands, just because closer islands are easier to reach. Extinction is lower on islands close to the mainland because of the likelihood of immigration. There is more of a chance that new immigrants will arrive and keep a species in existence on that island.
Rates of immigration to an island are mainly determined by the distance from the mainland to the island, and rates of extinction on the island are mainly determined by island size.
Image source credit goes to -http://www.islandbiogeography.org/
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