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
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controls the short time dynamic equilibrium of an island biota. The short time dynamic equilibrium keeps the number of species constant throughout the ecologic time. Evolution by natural selection plays the most notable role on the equilibrium in the long run (geologic time). Evolution attempts to change the equilibrium by increasing the number of species achieving equilibrium, thus attaining a new equilibrium state. The author provided a substantial amount of direct and indirect studies on insects, birds, and plant habitats conducted on oceanic islands or other insular areas that supports or proves the equilibrium theory. Simberloff (1974) elaborately described the short time dynamic equilibrium on island habitats, which acts on ecologic time scale.
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…
equilibrium. According to Simberloff (1974), the equilibrium model assumes equivalency in member species while considering the total number of species in equilibrium. However, Simberloff (1974) reasoned that the inaccuracy/ inappropriate inferences on nonequivalent colonizing member species or lack of congeneric species due to increased competition in poor-resourced areas can arise from numerical analysis rather than direct observation and autecological studies. Another important concept for island equilibrium is the taxon cycle, which plays an important role in the long term equilibrium condition.
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
region. In conclusion, as mentioned in Simberloff (1974), the dynamic island biogeographic equilibrium theory acts upon both the ecological and evolutionary time scale, which depends on small scale frequent events (extinction and emigration). The small scale frequent events control the number and composition of species in an island. The long term equilibriums are subjected to evolution by natural selection, which acts over large scale geological changes (sea level change, land bridge creation or destruction, fragmentation or unification of land masses). According to Simberloff (1974), the evolution of island biogeography has a potential benefit apart from the understanding of the insular habitat behavior. The island biogeographic equilibrium theory can be successfully applied to the understanding of the ecologic and evolutionary changes in the other similar insular habitats and can be used for the conservation of vulnerable ecosystems.
“It is a vision, a dream, if you prefer, like Martin Luther King’s, and it means clustering on a planetary scale.” (Nash) In Historian Roderick Nash’s essay entitled “Island Civilization: A vision for Human Occupancy of Earth in the Fourth Millennium,” Nash not only proposes the ideology of Island Civilization but also challenges readers to be informed of the rights of nature. Gaining insight on the options of preservation and nature from masterminds like John Muir, Henry David Thoreau, and Wallace Stegner. Nash devises a plan of action for Earth during the fourth millennium. Realizing the illustrate of our worlds “wilderness” Nash educates on the ways in which the natural world will evolve one thousand years from now.
...ted investigations of sediment archives in the crater lake of volcano Rano Raraku which contradict this hypothesis. On the basis of pollen data they found no evidence for a significant impact of rats proceeding anthropogenic woodland destruction” (2008, p. 24). Another scientist also found evidence that the rats were not abundant and was valued as currency for the Polynesian people. Brown (2006 [1924]) found that the Pacific rats were valued as currency by the islanders in the past, this report shows that rats were not abundant, but few on the island, and so the islanders will look at the animals as a valuable food source, not as a major environmental problem (2006 [1924]). Meith also conducted some research based on the intensive analysis of soils and sediments at several sites, and he also disagrees with the hypothesis of a major rat overpopulation (Mieth, 2010).
In the article "Island Civilization: A vision for human occupancy of earth in the fourth millennium" a very good point was made about how humans are not treating the earth with respect, however our generation still has a chance to turn the earth from cancerous to healthy.
Mills, Scott L., Daniel F. Doak, and Michael E. Soule. "The Keystone-species Concept in Ecology and Conservation." BioScience 43.4 (1993): 219-25. Apr. 1993. Web. 30 Oct. 2011.
Bibliography Allen, G. (2003). Roland Barthes. London: Routledge. 2007. Barthes, R. (1981). The Species of the World.
For example, if the larger fish are removed than its prey begins to overpopulate, due to the lack of population control. The balance in the oceans is an urgent problem, with around 90% of predatory fish stocks depleted. The ripples can extend even further to land creatures like seagulls.
A different scenario takes place when an alien species is transported to a new area. Although direct competition with similar species is still a problem, the new kid in the block may have no natural pests and diseases. Thus, large stands of monocultures can occur. It is generally accepted that one plant species will support 10 species of animals. If one species takes over 99% of a given habitat dozens if not hundreds of species are lost from that area and some populations are stressed enough that extinction is possible.
The stability of barrier islands is dependent on numerous dynamic factors, hence the efforts taken to keep the island as stable as possible. The combination of structures used to “protect” the island from natural disasters and the normal “life” of a barrier island is crucial. Without these protections, the island could be significantly altered by a single major meteorological event. If another event similar to the mass melting during the Holocene, or if the amount of sediment increases or decreases; the island could disappear altogether. Learning how the island formed and what factors affect its’ stability are the fundamental links to keeping Galveston Island the paradise it is today.
The eradication of species numbers average at a toll close to one hundred percent of earths total living creatures. “It is the Earth's most severe known extinction event, with up to 96% of all marine species and 70% of terrestrial vertebrate species becoming extinct” (Sahney, and Benton 759). Not only where marine and terrestrial species effected but this catastrophic event is the only recogni...
Landscape fragmentation contributes to loss of migratory corridors, loss of connectivity and natural communities, which all lead to a loss of biodiversity for a region. Conservation of biodiversity must include all levels of diversity: genetic, species, community, and landscape (CNHP 1995). Each complex level is dependent upon and linked to the other levels. In addition, humans are linked to all levels of this hierarchy. A healthy natural and human environment go hand in hand (CNHP 1995). An important step in conservation planning, in order to guarantee both a healthy natural environment as well as a healthy human environment, is recognizing the most endangered elements.
of species due to a variety of causes. Included is out competition, depletion of resources
An ecosystem is an identifiable system of interdependent relationships between living organisms and their biophysical environment. Ecosystems exist in a state of dynamic equilibrium. Meaning the ecosystem is constantly evolving while still remaining in a stable state. Coral reef ecosystems are long, narrow masses of coral and other substances the top of which is adjacent to the surface of the sea. Australia’s Great Barrier Reef (GBR) spans from 8°N and 24°S, stretching from the Fly River in Papua New Guinea to the southern Queensland (QLD) coast. The reef the largest living thing on earth, covers an area of 348000 km2 is composed of over 25000 individual reefs and 900 islands. However, the dynamic equilibrium of this complex ecosystem is being affected by both by both natural and human induced stresses which impacts nature, rate of change and functioning of the GBR. Accordingly, humans have introduced a number of strategies to stabilise the dynamic equilibrium of the GBR
Darwin’s observations from the islands made him want to come up with some explanation to why this occurred. He began to do research of each the species that had lived on these islands and observe all of the characteristics that had. He noticed that the islands h...
On the first level, when foreign, but previously non-invasive species is first introduced to a new area, the new species may play a role in a community that was previously unfulfilled; it may fill a vacant niche in the ecosystem. Originally this new species may be seen as a useful contributor to its new surroundings because it has only (temporarily) increased biodiversity in the area (Meinesz, 2003).
Lotze, Heike K., Marta Coll, Anna M. Magera, Christine Ward-Paige, and Laura Airoldi. "Recovery of Marine Animal Populations and Ecosystems." Trends in Ecology & Evolution 26.11 (2011): 595-605. Print.