III. Island Biogeography

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III. Island Biogeography
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III. Island Biogeography

• Biogeography The study of the distribution of
  organisms in space and time.

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Biogeography 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).

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Islands are important natural laboratories for
the study of biogeography, ecology, population
genetics, evolutionary biology, etc.
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Early naturalists (e.g., 16th-18th centuries)
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.
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Darwin observed dozens of animal species unique
to the Galapagos
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including 13 species of Galapagos Finches
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1859 - 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)
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1883 - Eruption of Krakatau (Krakatoa), a
volcanic island in Indonesia (Aug. 26-27).
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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?).
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Rakata and adjacent islands formed a laboratory
for study of island colonization and tropical
succession

• May 1884 - first researchers reach the islands
  find only a spider in a crevice on the south side
  of Rakata.
• October 1884 - grass shoots growing on Rakata.

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• 1886 - Botanists, and later zoologists, begin
  monitoring colonization of Rakata
• nine species of flowering plants present on
  beaches
• 1897 - 23 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

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1908 - 46 species of flowing plants and 13
species of birds present 1934 - 30 species of
birds present but, at least 5 bird species
present in early 20th century were now extinct on
Rakata
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• 50 of inland plant species on Rakata in 1897
  have become extinct however,
• since 1934, 16 additional families of higher
  plants have colonized.

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• colonization by new plant species was initially
  high, then dropped as available space became
  occupied by pioneer species
• immigration rate then increased as
• developing forests created new habitat (
  potential new ecological niches)
• as forests replaced grasslands, grasses, and
  insects and birds dependent on grasses, became
  extinct on island.

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• Biogeographical lessons from Krakatau
• Composition of plant and animal communities
• at any given time reflect
• colonization
• local extinction
• succession
• disturbance

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• 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. 1992 GeoJournal
  28.2 201-211.
• Whittaker, R.J. et al. 2000, J.
  Biogeograpy 27(5)1049-1064

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More recently, island biogeographers have begun
focusing on patterns and mechanisms of evolution
of island flora and fauna. Dr. Koning will
discuss thisstay tuned
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Types of Islands
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Continental Islands Formed on continent may
have formerly been connected to mainland by land
bridge
Island
Current Sea Level
Former Sea Level
Continent
Submerged Land Bridge
Continental Shelf
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Examples of Continental Islands

1. British Isles
2. California Channel Islands
3. Block Island, Nantucket, Marthas Vineyard

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British Isles Land mass is part of European
continent. During the last ice age, Britain was
connected to Europe by a plateau called
Doggerland.
Doggerland
Source New Scientist, 8 Nov. 2008
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As Ice Age ended, rising sea level flooded
Doggerland and formed English Channel.
Dogger Bank, an upland area of Doggerland,
outlined in red.
North Sea
England
France
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California Channel Islands Group of eight
islands off the California coast during last
ice age, some were connected to mainland by land
bridge.
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Block Island, Nantucket, Marthas 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
http//www.uwsp.edu/gEo/faculty/lemke/glacial_proc
esses/MoraineMovie.html
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Continental Islands Two Unusual Cases
1. San Salvadors offshore cays Rising sea level
caused erosion of San Salvador, leaving many
small, erosion- Resistant islands, or cays
(keys).
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Cays on the horizon (arrow) were once part of
San Salvador.
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Continental Islands Two Unusual Cases

• 1. San Salvadors offshore cays Rising sea level
  caused
• erosion of San Salvador, leaving many small,
  erosion-
• resistant islands, or cays (keys).
• 2. Terrestrial habitat islands Isolated region
  on larger
• land mass, such as
• mountain top
• forest remnant surrounded cleared land
• forest remnant on island in river or lake
• water-filled tree hole in forest

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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.
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B. Oceanic Islands Never connected to
continent usually formed by volcanic activity
and isolated from continent by deep ocean.
Oceanic Island
Current Sea Level
Former Sea Level
Continental Shelf
Undersea Volcano
Sea Floor
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Examples of Oceanic Islands

• Iceland
• Japan
• Aleutians
• Bermuda
• Caribbean Islands
• Hawaiian Islands
• South Pacific Atolls
• Et al.

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Many Caribbean islands were formed by volcanic
activity at subduction zone.
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Oceanic Islands Two Unusual Cases
New Zealand
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New Zealand Landmass represents the highlands of
a submerged continent called Zealandia. South
Island straddles two lithospheric plates and
subduction zone.
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Oceanic Islands Two Unusual Cases
New Zealand Bahamas
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Bahamas Banks No dry land connection to
continent?
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LandSat Image of San Salvador Island

• San Salvador sits on isolated portion of
  Bahamas Platform
• Surrounded by deep ocean
• Never connected to other Bahamian Bank islands,
  or to continent
• Qualifies as an oceanic island

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End of Slide Show 4/13/09Refer to Handouts
for Remainder of Lecture