THEORY OF ISLAND BIOGEOGRAPHY

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THE THEORY OF ISLAND BIOGEOGRAPHY

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Outline Introduction Definition of Island biogeography Historical background Founders of the theory The theory of island biogeography Immigration and Extinction Curves Example by a new Volcanic island Island Krakatoa Two main predictions Implications of Island Biogeography

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An island is any area of suitable habitat surrounded by an expanse unsuitable habitat.

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Biogeography Biogeography is the study of the distributions of plants and animals over the surface of the Earth in both space and time.

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Island Biogeography It is a field within biogeography that attempts to establish and explain the factors that affect the species richness of natural communities.

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Historical Background Static Assumption: Island Composition Mixed Pattern recognized by Forster and de Candolle Lack, Mayer (1940’s) and Hutchinson (1950’s)

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Robert MacArthur and Edward O. Wilson coined the term “Theory of Island Biogeography” as this theory attempted to predict the number of species that would exist on newly created island. Founders of the “Island Biogeography” theory

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Two eminent ecologist, the late Robert MacArthur of Princeton University and Edward O. Wilson of Harvard developed a theory of “Island Biogeograpy” to explain uneven distribution of species. Founders of the “Island Biogeography” theory

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In the theory's simplest form species from the source area disperse to an island at a rate (the immigration curve) depending on the distance of the island from the source area. The fewer species are on the island, the higher the immigration curve. The more species on the island, the lower the curve because most potential new immigrant species will have already reached the island. The Immigration Curve

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The immigration curve for islands close to the source area should be fairly vertical because the potential immigrants should reach the island fairly rapidly and then fall off sharply as the number of potential new immigrant species from the source area decreases. Similarly islands far from the source area should have a more horizontal immigration curve because new immigrating species take longer to get to far away islands than to those closer into the source area The Immigration Curve

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Similarly there is a rate at which species go extinct on the island (the extinction curve). The more species there are on the island, the higher the extinction rate. The Extinction Curve

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The slopes of the lines depend on the size of the island and its distance from the source area. For a small island the extinction rate should increase more rapidly (the line should be more vertical) as the number of species on the island increase because smaller islands have fewer potential habitats and resources to colonize. Larger islands should have a more horizontal extinction rate (relative to the number of species already there) because there are more potential habitats and resources to use. The slope of the extinction curve, therefore, depends on the size of the island. The Extinction Curve

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In 1883, there was a catastrophic volcanic explosion that devastated the island of Krakatoa, located between the islands of Sumatra and Java.

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The flora and fauna of its remnant and of two adjacent islands were completely exterminated, yet within 25 years (1908) thirteen species of birds had recolonized what was left of the island. By 1919-21 twenty-eight bird species were present, and by 1932-34, twenty-nine. Between the explosion and 1934, thirty-four species actually became established, but five of them went extinct. By 1951-52 thirty-three species were present, and by 1984-85, thirty-five species.

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During this half century (1934-1985), a further fourteen species had become established, and eight had become extinct. As the theory predicted, the rate of increase declined as more and more species colonized the island. In addition, as equilibrium was approached there was some turnover. The number in the cast remained roughly the same while the actors gradually changed.

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Islands close to a source area should have a higher number of species than islands further from the source area for islands of equivalent areas. Larger islands should have more species than smaller islands for islands located at similar distances from the source area. These two predictions have been largely supported by observational and experimental data. The two main predictions of Island Biogeography are:

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Implications of Island Biogeography Modern science uses island biogeography theory to understand species today and to help endangered species. The theory of island biogeography is important to conservation biology because it helps scientists predict how many species should thrive in a given area and gives them information on how to develop protective reserves.

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Overall, island biogeography is an important concept that helps people understand species distribution around the world and assists in the preservation of ecosystems and the animals in them which might otherwise be lost.

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Two eminent ecologist, the late Robert MacArthur of Princeton University and Edward O. Wilson of Harvard developed a theory of “Island Biogeograpy” to explain uneven distribution of species. For more references

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presented by: Dionisio, Van Russ Jade P. Enriquez, Cara Mae D. Gascon, Sweet Ariane Gay Lagare, Nickel Jean S. Perigrino, Susan

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