III. Island Biogeography
III. Island Biogeography
Biogeography: The study of the
distribution of organisms in space and
time.
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).
Islands are important natural laboratories for the
study of biogeography, ecology, population
genetics, evolutionary biology, etc.
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.
Darwin observed dozens of animal
species unique to the Galapagos
…including 13 species of
Galapagos Finches
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)
1883 - Eruption of Krakatau (Krakatoa), a
volcanic island in Indonesia (Aug. 26-27).
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?).
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.
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;
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;
• ~ 50% of inland plant species on Rakata
in 1897 have become extinct; however,
• since 1934, 16 additional families of
higher plants have colonized.
• 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.
Biogeographical lessons from Krakatau:
Composition of plant and animal communities
at any given time reflect
• colonization
• local extinction
• succession
• disturbance
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
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
Types of Islands
A.
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
Examples of Continental Islands
1. British Isles
2. California Channel Islands
3. 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.
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Doggerland
Source: New Scientist, 8 Nov. 2008
As Ice Age ended, rising sea level flooded
Doggerland and formed English Channel.
North Sea
Dogger Bank, an
upland area of
Doggerland,
outlined in red.
England
France
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.
QuickTi me™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Click to Play Animation
http://www.uwsp.edu/gEo/faculty/lemke/glacial_processes/MoraineMovie.html
Continental Islands:
Two Unusual Cases
1. San Salvador’s offshore cays: Rising sea level caused
erosion of San Salvador, leaving many small, erosionResistant islands, or cays (“keys”).
Cays on the horizon (arrow) were once
part of San Salvador.
Continental Islands:
Two Unusual Cases
1. San Salvador’s offshore cays: Rising sea level caused
erosion of San Salvador, leaving many small, erosionresistant 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
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.
Oceanic
Island
Current Sea Level
Continental
Shelf
Former Sea
Level
Sea Floor
Undersea
Volcano
Examples of Oceanic Islands
• Iceland
• Japan
• Aleutians
• Bermuda
• Caribbean Islands
• Hawaiian Islands
• South Pacific Atolls
• Et al.
Many Caribbean islands were formed by
volcanic activity at subduction zone.
Oceanic Islands:
Two Unusual Cases
New Zealand
New Zealand: Landmass represents the highlands of
a submerged continent called Zealandia. South
Island straddles two lithospheric plates and
subduction zone.
Oceanic Islands:
Two Unusual Cases
New Zealand
Bahamas
Bahamas Banks: No dry land connection to continent?
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
End of Slide Show
4/13/09
Refer to Handouts for
Remainder of Lecture