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Wallacea
The Wallacea region is
located almost entirely
within the borders of
Indonesia and includes
the large island of Sulawesi,
the Moluccas (Spice islands),
Banda islands and the
Lesser Sundas. The hotspot
covers a total land area
of total land area of
338,494 km².
The Lesser Sundas are
located south of Sulawesi,
and include Bali, Lombok,
Sumba, Sumbawa, Flores
and Timor. The Moluccas
includes several hundred
islands in the north-east
of the hotspot, the largest
being Seram and Halmahera.
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| Wallace's
line
The Wallacea hotspot
is separated from the
adjacent Sundaland hotspot
to the west by Wallace's
line, which runs between
Borneo and Sulawesi to
the north and Bali and
Lombok to the south. Wallace's
line is named after the
British naturalist Alfred
Wallace, who noted distinct
bird and mammal faunas
on either side of the
line. Wallacea is a transition
zone between Asian and
Australasian regions,
containing flora and fauna
from both of these areas.
Many mammals originate
from Asia whilst birds
have Australasian origins.
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| Why
is Wallacea high in endemic
species?
Wallacea contains a high
number of endemic species.
Several factors explain
why the region in rich
in endemics:
1.) Tropical climate:
High temperatures are
thought to lead to high
rates of mutation, and
therefore high rates of
speciation.
2.) The region contains
many islands: Isolation
is a major factor leading
to the formation of endemic
species. Islands are isolated
because they are surrounded
by areas of sea, which
represents a barrier to
migration. Isolated species
on islands may evolve
into unique species adapted
to their local habitat/ecological
niches.
3.) Geological history:
Wallace's line marks the
position of deep ocean
trenches and separates
shallow waters to the
west from the deeper waters
to the east. During past
ice-ages, sea levels dropped
and the shallow waters
to the west disappeared,
allowing migration of
fauna between the islands
of Java, Borneo, Sumatra
and Bali and therefore
spread of similar species
between them. Islands
to the east in the Wallacea
region remained isolated
by the deep ocean waters,
preventing migration of
species and leading to
the evolution of distinct
faunas.
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Wallace's
line
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Although Wallacea
contains fewer species overall
compared to the Sundaland hotspot
to the west, the region contains
a very high number of endemic
species for it's size:
Table
1: Total number of
species and number of endemic
species for various taxonomic
groups
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Taxonomic
group
|
Number
of species
|
Number
of endemic Species
|
Percent
endemism
|
|
Plants
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10 000
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1500
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15
|
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Mammals
|
222
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127
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57.2
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Birds
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647
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262
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40.5
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Reptiles
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222
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99
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44.6
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Amphibians
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48
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33
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68.8
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Freshwater
fish
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250
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50
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20
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Ecosystems
The principle terrestrial vegetation
is tropical rainforest, but
there are also large areas of
savannah grassland on the Lesser
Sundas. The Wallacea hotspot
also includes some of the most
biologically diverse coral reefs
in the world. The World Wildlife
Fund lists several regions in
Wallacea as Global 200 ecoregions,
a collection of the Earth's
most biologically diverse and
representative terrestrial,
freshwater, and marine habitats.
These include Sulawesi moist
forests, Moluccas moist forests,
Nusa Tengarra (Spice islands)
dry forests, central Sulawesi
lakes and the Sulu-Sulawesi
and Banda-flores seas (tropical
coral).
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