Island Biogeography Theory

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In the review article, “Equilibrium Theory of Island Biogeography and Ecology”, Simberloff (1974) described how the equilibrium hypothesis can be used to explain island biogeography. According to the author, islands offer significant scientific, economic, evolutionary, or ecologic importances due to their unique characteristics (isolation, insular depauperization). However, detailed study on the somewhat puzzling island biogeography is limited. Therefore, Simberloff (1974) provided an in-depth research on the evolution of the island biogeography from an idiographic discipline to nomothetic science.
According to Simberloff (1974), the revolutionized equilibrium theory of island biostratigraphy states that species immigration and extinction …show more content…

Based on direct study results from literature, Simberloff (1974) identified two factors that dominate short term equilibrium conditions: distance effect and area effect. These two factors influence the island equilibrium as follows: closer islands carry larger number of equilibrium species and larger turn-over rates (distance effect) and larger islands carry larger number of equilibrium species but smaller turn-over rates (area effect). Simberloff (1974) pointed out extinction as the more pronounced factor on smaller islands than the larger ones, because of low carrying capacities of smaller islands. Another important concept in island equilibrium is critical population size, which has a significant effect on area and number of species attaining …show more content…

According to Simberloff (1974), taxon cycle determines the rates of immigration and extinction of species, thus influencing the number of species present in the short-term equilibrium. Taxon cycle is also responsible for increased probability in equilibrium disharmony or sympatry in colonizing species as well as competition between species. The influences of taxon cycle on equilibrium is supported by various studies conducted on birds, insects and lizards.
In sum, three equilibrium conditions prevail in island biogeography:
1) The taxon cycle: acts on long term basis, exerts pressure on short-term equilibrium depending on species number at equilibrium and degree of sympatry, involves immigration, extinction and speciation.
2) The long term geologic changes: acts on taxon cycle, involves sea level change, land bridge creation or destruction, fragmentation or unification of land masses.
3) The short term balance in immigration and extinction: produces highly coadapted community due to the rise in number of species attaining equilibrium, which decreases niche width and extinction. In this case, carrying capacity increases until dramatic extinction follows. Thus, the exact carrying capacity for short term equilibrium depends on taxon cycle, island size, and bigeographic

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