III. Island Biogeography. III. Island Biogeography. Biogeography : The study of the distribution of organisms in space and time. Biogeography looks at four fundamental processes:.
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Biogeography: The study of the distribution of organisms in space and time.
1. Dispersal: Movement of organism(s) from a point of origin (= location of source, or ancestral, population) to a new location.
2. Colonization: Organism reaches new location, survives, reproduces, and establishes new population.
3. Extinction: Species is eliminated from a particular area (i.e., no more reproducing individuals present); species may survive elsewhere, and may re-colonize area where it went extinct.
4. Evolution: Surviving population in a particular area undergoes change(s) in frequency of gene alleles; may result in altered phenotype, and, given sufficient time, possibly the formation of new species (= speciation).
exploring isolated islands noted new types
of plants and animals, which were often
distinctive for each island or island group.For several centuries, scientific focus was on
cataloging the diversity of island organisms.
Darwin speculated on possible means by which organisms colonized islands and evolved into new species (e.g., Galapagos finches)
Half of Krakatau was blown away; remaining portion, Rakata (a volcanic cone), plus neighboring islands, left covered with 30-60 m of pumice and ash (= sterile landscape?).
1886 - Botanists, and later zoologists, begin monitoring colonization of Rakata:
~ 50% of inland plant species on Rakata in 1897 have become extinct; however,
colonization by new plant species was initially high, then dropped as available space became occupied by pioneer species;
Recent studies* have re-evaluated ecological succession and extinctions on Rakata and adjacent islands since 1883:
More recently, island biogeographers have begun focusing on patterns and mechanisms of evolution of island flora and fauna.
Current Sea Level
Submerged Land Bridge
California Channel Islands
Block Island, Nantucket, Martha’s Vineyard
British Isles: Land mass is part of European continent. During the last ice age, Britain was connected to Europe by a plateau called Doggerland.
Source: New Scientist, 8 Nov. 2008
Dogger Bank, an upland area of Doggerland, outlined in red.
California Channel Islands:Group of eight islands off the California coast; during last ice age, some were connected to mainland by land bridge.
Block Island, Nantucket, Martha’s Vineyard: Coastal wedge sediment islands formed by glacial deposits (terminal/recessional moraines); probably no dry, passable connection to mainland since last Ice Age. Long Island is also of this type.
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1. San Salvador’s offshore cays: Rising sea level caused
erosion of San Salvador, leaving many small, erosion-
Resistant islands, or cays (“keys”).
Barrow Colorado Island (BCI): A 1500 hectare remnant of lowland moist forest in the middle of the Panama Canal; it is managed by the Smithsonian Institute as a tropical research site.
B. Oceanic Islands: Never connected to continent; usually formed by volcanic activity and isolated from continent by deep ocean.
Current Sea Level
Former Sea Level
New Zealand:Landmass represents the highlands of a submerged continent called Zealandia. South Island straddles two lithospheric plates and subduction zone.