2III. Island Biogeography Biogeography: The study of the distribution of organisms in space and time.
3Biogeography looks at four fundamental processes: 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).
4Islands are important natural laboratories for the study of biogeography, ecology, population genetics, evolutionary biology, etc.
5Early naturalists (e.g., 16th-18th centuries) exploring isolated islands noted new typesof plants and animals, which were oftendistinctive for each island or island group. For several centuries, scientific focus was oncataloging the diversity of island organisms.
6Darwin observed dozens of animal species unique to the Galapagos
81859 - Publication of “On the Origin of Species” Darwin speculated on possible means by which organisms colonized islands and evolved into new species (e.g., Galapagos finches)
91883 - Eruption of Krakatau (Krakatoa), a volcanic island in Indonesia (Aug. 26-27).
10Half of Krakatau was blown away; remaining portion, Rakata (a volcanic cone), plus neighboring islands, left covered with m of pumice and ash (= sterile landscape?).
11Rakata and adjacent islands formed a laboratory for study of island colonization and tropical succession:May first researchers reach the islands; find only a spider in a crevice on the south side of Rakata.October grass shoots growing on Rakata.
121886 - Botanists, and later zoologists, begin monitoring colonization of Rakata: nine species of flowering plants present on beaches;species of flowing plants present;development of coastal forest provided seeds and fruits for colonizing bats and birds;ferns (with spores that can be dispersed by wind) were first colonizers away from the coast;
131908 - 46 species of flowing plants and 13 species of birds present; species of birds present; but,at least 5 bird species present in early 20th century were now extinct on Rakata;
14~ 50% of inland plant species on Rakata in 1897 have become extinct; however, since 1934, 16 additional families of higher plants have colonized.
15colonization by new plant species was initially high, then dropped as available space became occupied by pioneer species;immigration rate then increased asdeveloping forests created new habitat (= potential new ecological niches);as forests replaced grasslands, grasses, and insects and birds dependent on grasses, became extinct on island.
16Biogeographical lessons from Krakatau: Composition of plant and animal communitiesat any given time reflectcolonizationlocal extinctionsuccessiondisturbance
17Few naturally colonizing and established species have become extinct. Recent studies* have re-evaluated ecological succession and extinctions on Rakata and adjacent islands since 1883:Most plant extinctions have been species introduced by people, and rare or ephemeral species;Few naturally colonizing and established species have become extinct.*e.g., Whittaker, R.J. et al GeoJournal 28.2:Whittaker, R.J. et al. 2000, J. Biogeograpy 27(5):
18Dr. Koning will discuss this…stay tuned More recently, island biogeographers have begun focusing on patterns and mechanisms of evolution of island flora and fauna.Dr. Koning will discuss this…stay tuned
20Continental Islands: Formed on continent; may have formerly been connected to mainland by land bridge:IslandCurrent Sea LevelFormerSea LevelContinentSubmerged Land BridgeContinental Shelf
21Examples of Continental Islands British IslesCalifornia Channel IslandsBlock Island, Nantucket, Martha’s Vineyard
22British Isles: Land mass is part of European continent British Isles: Land mass is part of European continent. During the last ice age, Britain was connected to Europe by a plateau called Doggerland.DoggerlandSource: New Scientist, 8 Nov. 2008
23As Ice Age ended, rising sea level flooded Doggerland and formed English Channel. Dogger Bank, an upland area of Doggerland, outlined in red.North SeaEnglandFrance
24California Channel Islands: Group of eight islands off the California coast; during last ice age, some were connected to mainland by land bridge.
25Block 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.Click to Play Animation
26Continental Islands: Two Unusual Cases 1. San Salvador’s offshore cays: Rising sea level causederosion of San Salvador, leaving many small, erosion-Resistant islands, or cays (“keys”).
27Cays on the horizon (arrow) were once part of San Salvador.
28Continental Islands: Two Unusual Cases 1. San Salvador’s offshore cays: Rising sea level causederosion of San Salvador, leaving many small, erosion-resistant islands, or cays (“keys”).2. Terrestrial habitat islands: Isolated region on largerland mass, such asmountain top;forest remnant surrounded cleared land;forest remnant on island in river or lake;water-filled tree hole in forest
29Barrow 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.
30B. Oceanic Islands: Never connected to continent; usually formed by volcanic activity and isolated from continent by deep ocean.Oceanic IslandCurrent Sea LevelContinental ShelfFormer Sea LevelUnderseaVolcanoSea Floor
31Examples of Oceanic Islands IcelandJapanAleutiansBermudaCaribbean IslandsHawaiian IslandsSouth Pacific AtollsEt al.
32Many Caribbean islands were formed by volcanic activity at subduction zone.
34New Zealand: Landmass represents the highlands of a submerged continent called Zealandia. South Island straddles two lithospheric plates and subduction zone.
35Oceanic Islands: Two Unusual Cases New ZealandBahamas
36Bahamas Banks: No dry land connection to continent?
37LandSat Image of San Salvador Island San Salvador sits on isolated portion of Bahamas PlatformSurrounded by deep oceanNever connected to other Bahamian Bank islands, or to continentQualifies as an oceanic island
38End of Slide Show 4/13/09 Refer to Handouts for Remainder of Lecture