Loses of biodiversity on
islands
Island biodiversity
• Islands have a very high level of endemism,
contributing disproportionably to their size to
biodiversity
• Many classic examples of adaptive radiation
and lineage diversification (Hawaiian orchids,
Drosophila, honeycreepers, land snails) may
be found among the world's islands.
• For the same reason that these species are
endemic, they are very vulnerable to
extinctions.
Islands as global hotspots of biodiversity
• Out of 25 global hotspots of biodiversity 8 are on
islands: Caribbean 3, Madagascar 9, Sundaland
(Malay.+Indon.)16, Wallacea 17, Philippines 18, New
Caledonia 23, New Zealand 24, PolynesiaMicroneasia 25
Islands as global hotspots of biodiversity
Brooks et al 2002
Natural reduction of biodiversity
• Islands are highly vulnerable to natural disturbances like
hurricanes. Spiller et al. (1998) assessed responses of spiders
and lizards to disturbance caused by hurricane Lili on the
Bahama Islands.
• larger bodied animals (ie. lizards) were less vulnerable to
being killed during the hurricane than spiders, though the smallbodied spider populations responded more quickly after the
hurricane had passed.
• extinction (or more properly extirpation) from islands was
related to population size only when disturbance was moderate,
but not when it was intense.
• After catastrophic disturbance, recovery rates of different
species were related to their dispersal abilities. Lizards,
the least capable dispersers, were absent from many suitable
islands, likely a long-lasting effects of catastrophes.
Impact of Hurricane Lilly on Islands in the
Bahamas
Hurricane Lili
hit these
islands with
a 5m storm
surge and
90knot winds
(Spiller
1998)
Natural reduction of biodiversity
The time scale and effect of disturbances can vary
greatly (Whittaker 1998)
Natural reduction of biodiversity
Fossil record found 0-3 vertebrate population
losses for 4000-8000 years prior to humans on
the Galapagos Islands
Bone finds in a cave on Tonga reveal little
prehuman species turnover
Despite the fact that islands are subject to natural
disasters like drought, fire and cyclones, to date
the fossil record has revealed no major loss of
species from natural causes (Steadmann 1995)
Natural dispersal does still occur
• Biodiversity on islands is the product of
immigration, extinction, and in situ speciation (in
some cases).
• After good dispersers colonize, the rate of
new, natural species additions may be very low.
Nevertheless, it does occur.
• The green iguana lizard Iguana iguana
colonized the island of Anguilla following a
series of hurricanes in the Lesser Antilles in
1995. The storm tracks were east-northwest.
• The iguanas are believed to have originated on
the island of Guadeloupe, 300 km away Censky
et al. (1998). This lizard was previously
unknown on Anguilla.
•
After the storms, a large mat of logs and uprooted
trees washed ashore on Anguilla. Based on local
observations, it is believed that at least 3 male and 5
female lizards were found on and around the mat on
the beach on Anguilla. One female was in a
reproductive condition, making it possible that this
colony of immigrants could establish on the island.
Prehistoric spread of humans
• The earliest islands colonized by sea-faring peoples were
Australia, New Guinea, New Ireland, Sulawesi (Indonesia), and
the Solomon Islands (earliest islands colonized are listed
first). Each of these islands were colonized at least 28,000
years ago. Each of these islands lie in, or west of, the
Melanesian Island chain.
• Further north and east, the Micronesian Islands (Caroline
Islands, Marshall Islands, Gilbert Islands and Mariana Islands)
were colonized about 4000 years ago.
• Further east and south, Fiji and New Caledonia (both in
Melanesia) and Somoa and Tonga (both part of Polynesia)
were colonized between 3500 and 3000 years ago. Further
east in the Polynesian chain, the Marquesas Islands, Cook
Islands, Hawaiian Islands, Society (Tahiti) Islands and Easter
Island were colonized in 1500-2000, 1600, 1400, 1200, and
1000-1300 years ago, respectively. New Zealand, far south of
these island groups, was among the last island groups
colonized (800 years ago) owing to its extreme isolation.
Prehistoric spread of humans in Polynesia
Due to a low level of resolution among the human populations,
Pacific rat mtDNA was used to reconstruct human dispersal
(Matisoo-Smith et al 1998). Australia, New Guinea, New Ireland,
Indonesia, and Solomon Islands at least 28,000 years ago;
Micronesian Islands (Caroline Islands, Marshall Islands, Gilbert
Islands and Mariana Islands) were colonized about 4000 years
ago
Fiji, New Caledonia,
Samoa and Tonga: 3500
and 3000. Marquesas
Islands 1500-2000, Cook
Islands 1600, Hawaiian
Islands 1400, Society
(Tahiti) Islands 1200 and
Easter Island 1000-1300
New Zealand, was among
the last island groups
colonized (800 years ago)
Island extinction
The causes of bird extinctions on islands are due to human
and non-native mammal (rats, dogs and pigs) predation.
Removal or alteration of forests through cutting, burning and
introduction of non-native plants
Soil erosion through deforestation has eliminated nesting
sites for burrowing seabirds
The rate of extinction after human arrival varied greatly from
only 100 years in many cases (iguanas and birds)
(Steadman 2002) to several thousand years, depending on
island size, habitat diversity, island ruggedness and human
population levels and continuity.
Modern extinctions caused by similar processes than
historic, only the tools have changed (Steadman 1995)
Prehistoric extinctions
Example of Easter Islands bird
species (Steadman 1995)
On one island in the Marquesas
the number of nesting seabirds
went from 22 to 4.
On one island on the Society
Islands nesting birds went from
15 to 4
Galapagos Islands were only
settled by Europeans. Excellent
fossil records show 0-3
vertebrate population losses for
4000-8000 years prior to
humans, but 21-24 after human
arrival
Prehistoric extinctions
Human colonization of Pacific Islands resulted in large numbers
of bird extinctions, numbering ~2000 species (mainly flightless
rails), or 20% of global bird diversity.
Particularly hard hit with extinction or extirpation were rails,
pigeons, doves, parrots and passerines. Seabirds (mainly
shearwaters and petrels) have suffered more from
extirpation than extinction. Processes responsible for
extinctions caused by prehistoric peoples apparently are similar
to those today.
It is estimated that 90% of extinct bird species were inhabitants of
islands
More Polynesian bird species are extinct today from human
causes than are alive today, and many of the survivors have
greatly reduced ranges
Bird extinctions
Decline in bird species on a Tonga
Island depending on foraging
height and food type
Frugivores declined very sharply
with a negative effect on tree
pollination
Ground feeders (7-0) became
extinct caused by human and
non-native mammal predation
Steadman 1995)
Endemic Island Biota Extinction or Endangerments
More than 10% of Hawaii's tremendously diverse plant
species are extinct, and another 40% are
endangered;
Most of the 331 described species of endemic
Amastridae (family) snails of Hawaii are extinct, and
most of the survivors are tree-dwelling species
The land snail fauna of the Hawaiian islands once
numbered more than 750 species (>99% of which
were endemic to the islands), though most are now
either extinct or endangered.
The primary cause of species decline are introduction
of nonindigenous species (e.g. carnivorous snails),
and, to a lesser extent, destruction or modification of
habitat (Cowie 1998).
• Argentine ants (Iridomyrmex humilis) was introduced to
Maui (Hawai'i) 25 years ago and presently restricts the
distributions of many gastropods and arthropods.
• Some of those arthropods are major pollinators of
endemic plant species, predators, and flightless taxa
(wolf spiders and Collembolans)(Cole et al. 1992).
• The little red fire ant (Wasmannia auropunctata) was
first introduced to Indefatigable (Galapagos Islands)
early this century; it has since spread to 4 other islands
in the archipelago.
• At least 17 of the 28 ant taxa on the Galapagos have
limited distributions or abundances resulting from
aggressive encounters from the little red fire ant. It
also eliminated 1 scorpion and 2 spider species (Lubin
1984).
Reasons for the high loss of biodiversity on islands
In a meta analysis of a number of factors describing islands
(latitude, area, elevation, isolation, colonization), and comparing
them with the number of bird species extinct (Blackburn &
Gaston 2005)
The proportion of bird species extinct was best predicted by the
isolation of an island and time since colonisation, meaning the
more isolated and the earlier an island was colonized the more
bird species are extinct
Hence the less new migrants arrive in an ecosystem the less its
prepared to deal with them particularly if they arrive at high
rates
There is also evidence that human population densities were
higher on more isolated islands
The species most likely to become extinct were large bodied,
flightless, ground-dwelling or ground-nesting
Causes of Island-based Species
Extinctions
• Direct habitat destruction
• Introduced Species
• Overharvesting
• Depletion of food resources
Direct habitat destruction
• Direct habitat destruction associated with cutting or burning
of forests for agriculture, construction, and wood
extraction. All Polynesian islands were largely or completely
forested prior to man's arrival; many of these islands have only
small remnants, if any, left of this original vegetation.
• On Easter Island, loss of forest cover corresponded not only
with massive species losses, but also in human misery. It is
believed that the people on this island lost their
primary transportation mode (boats), and then their food
supply (marine mammals) following loss of forest cover.
• Archaeological records indicate a switch in diet from marine
foods to rats prior to the civilization's demise. Soil erosion
associated with deforestation has also resulted in loss of
nesting sites for some seabirds.
Introduced Species
• Animals such as feral goats, pigs, cats, dogs
and especially rats (European species: Rattus
rattus, Rattus norvegicus; Pacific species Rattus
exulans) caused major damage to native
vegetation, or competed with or preyed on
native taxa.
• Some introduced plants (Miconia in Tahiti;
Psidium in Tubuai, Leucaena in Marquesas,
Myrica in Hawaii) crowd out native taxa and form
monospecific stands.
Overharvesting
• Many taxa had limited distributions (endemics)
and thus were vulnerable not only to
extirpation but also to extinction if
exploited heavily.
• Some flightless birds were almost certainly
driven extinct because they evolved in
the absence of mammalian predators and
competitors and were unwary (=naive) of
human presence and were easily captured.
• It has been speculated that easy access to
these often abundant food sources was
an important factor permitting long distance
sea voyages by Polynesians and Europeans.
Depletion of food resources
• In some cases, extinctions were precipitated
by loss of food resources associated with
destruction of habitat or introduced species.
• For example, the New Zealand eagle
Harpagornis moorei was likely dependent on
moas and other large extinct birds.
• Rats (R. exulans) may have caused
invertebrate declines which reduced food
supplies for the extinct birds Aptornis and
Megaegotheles.
The island of Singapore
• On the island of Singapore, habitat loss over the past 183 years
exceeded 95%! Corresponding with this decline was a massive
documented or inferred loss of biodiversity.
• Losses were highest for forest specialists (34-87% of taxa
extinct) in taxa like butterflies, birds, fish and mammals.
• Loss rates were lower (5-80%) for vascular plants, decapods,
amphibians and reptiles.
• More than 50% of Singapore’s residual native biodiversity is
sheltered in reserves that account for only 0.25% of the island.
• Extrapolation of these patterns using species-area
relationships, reveal that 13-42% of regional populations will be
lost over the coming century, and at least half of these will be
losses of entire species (Brook et al. 2003)
The island of Singapore
Plant species in Tonga
• On the Island of Vava’o human arrived 2600 B.P.
identified by charcoal in the sediment core indicating
burning of the hardwood forest
• Increased soil erosion as documented by clay
particles in sediments
• The number of frugivorous and nectarivous bird
species was reduced from 19 to 6 species after
human arrival
• Among the extinct species are the two largest pigeon
species on Tonga
• Several large rainforest tree species with large seeds
have lost their means of seed dispersal (Fall 2005)
• Several tree species are not present anymore
Lizards and shrubs
• On the Island of Menorca a frugivorous lizard
became extinct after the introduction
carnivourous mammals (Traveset & Riera 2005)
• The lizard consumed large amounts of the
shrubs’ fruits and disperse them through their
scat. They were found to be the sole disperser of
seeds of a perennial shrub
• On the islands without the lizard the shrub only
recruits underneath the parent plant
• This is the most likely reason why this plant is
endangered
The brown tree snake
(Boiga irregularis)
• It’s native in Australia and was introduced accidentally onto
Guam in the 1950’s
• Overall responsible for the extinction of 3 out of 4 pelagic birds;
9 out of 13 forest birds; 3-5 out 12 reptile species on the Island
of Guam.
• This snake caused the extirpation or serious reduction of most
of the island's 25 resident bird species on the main island of
Guam.
• Twelve species were likely extirpated as breeding residents on
the main island, 8 others experienced declines of greater than
or equal to 90% throughout the island or at least in the north,
and 2 were kept at reduced population levels during all or much
of the study.
• Declines of greater than or equal to 90% occurred rapidly,
averaging just 8.9 years along three roadside survey routes
combined and 1.6 years at a 100-ha forested study site (Wiles et
al 2003, Rodda 1998).
(Wiles et al
2003)
New Zealand
• The islands were colonized by humans only 1000-800 years
ago because of their isolation. Endemism is high on oceanic
islands in this group, though diversity is lower than on the larger
(continental) islands.
• The archipelago has extraordinary biodiversity including 75% of
the world's penguins, 54% of seabirds (albatross, petrels, and
shearwater), 80% of baleen whales, 50% of beaked whales and
36% of dolphins. The islands also support many endemic
species, including 35% of macroalgae, 55% of sponges, 45% of
bryozoans, 20% of fish, and 30% of seabirds.
• This tremendous diversity has resulted from the islands' range
of climates (subtropical to subantarctic), isolation (oceanic to
continental), latitudinal diversity, and age.
• Over the past 200 years, 48% of the native avifauna has been
rendered extinct owing to habitat destruction and introduced
mammals (see below). Other factors responsible for destruction
of endemic avifauna (particularly flightless birds) include
overhunting and collections.
New Zealand
Reasons why New Zealand's biodiversity
still is high:
• human colonization was so recent, large
tracts of evergreen forest remain
• introductions were limited to the mainland
areas, thus preserving biodiversity on
smaller, adjacent islands
• public demand for preserving species and
restoring ecosystems.
New Zealand
• 120 eradication programs have created 'new' habitats for the
500 or more species threatened on the archipelago. New
Zealanders are also trying to rid the archipelago of ornamental
plants introduced by British colonists 'acclimatization societies'
• Reforestation programs aimed at restoring native vegetation
and habitats have proven successful, and in some cases have
helped endangered animals recover.
• For example, the black robin (Petroica traversi) numbered only
9 individuals in 1975; the 7 (2 breeding pairs) birds were
captured in 1976-1977 and moved from its degraded habitat on
Little Mangere Island to Mangere and later to South East
Islands. These larger islands had much better (and improving)
forest conditions. The species was on the brink of extinction
(10-15 individuals) for 8 more years before eggs were crossfostered with Chatham Island Tits, which increased production
of black robin fledglings. In 1992 the species totalled 120 birds.
• Helicopter-dispersed rodenticide eliminated rats from Red
Mercury Island after the 20 resident tuataras were
removed. These individuals have been in a captivebreeding program, and will soon be re-established on the
rat-free island. Two rare skinks will also be reintroduced to
the island. Programs of ecological restoration and habitat
rehabilitation are ongoing on many of the nation's islands
and are critical to survival of many endemic plants and
animals.
• Captive breeding programs are presently helping two
endangered flightless birds: the nocturnal parrot Kakapo
(Strigops habroptilus), of which 50 individuals remain, and
the gallinule Takahe (Porphyrio mantelli), of which 150
individuals remain (Clout and Craig 1994). These
species were both thought extinct before small populations
were found.
Chatham Island black robin
tuatara
kakapo
takahe
Kakapo example (Elliot 2001)
The Kakapo (Strigops habrotilus) is a
large parrot (1.5-4kg) endemic to New
Zealand and on of the worlds rarest birds
(62 individuals)
It’s a flightless, nocturnal, herbivorous, lek breeder that
breeds only every 2-5 years and leaves the eggs unattended
for long times
While protected from visual predators, predators hunting by
smell can are a threat. Rats and dogs were introduced by the
Polynesians and Europeans introduced rats, cats, mustelids
(ferrets and weasels); all prey on Kakapos
Additionally the native forest is reduced in large areas, but
the main problem is predation
By the 1970 only two populations on Stewart Island and in
the Northern Fjordland remained
Due to high mortality of adult parrots caused by cats, all animals
were translocated to three relatively predator free islands in the
1980s-1990s
Adult survival was between 98-99%, but only three chicks were
reared until 1995, leading to a much more intensive and intrusive
management of the species
As the Kakapo nesting seem to coincide with large crops of fruits
and seeds every 3-4 years, supplementary feeding was used to
increase the breeding frequency. Feeding also reduced the
amount of time the female was away from the eggs.
A total of 15 chicks have fledged since 1995
In order to prevent any further loss of eggs or chicks to predators
all nests were continuously monitored and traps and deterrents
were used to remove predators
Between 1981-1994 43% of the nestlings were eaten by rats.
Since intensified protection the overall chick mortality has
dropped from 75% to 29%
Potentially infertile males are removed to other islands
The last remaining male of a different island population was
moved to an island with several females
Eggs or chicks which were considered failing were removed from
the nests and hand reared and later released
Vertebrate invaders in New Zealand
Invader control
Removal of invasive species is an expensive and labour
intensive approach
Low level control efforts may help protect select native species,
current eradication methods,limited conservation funds, and the
potential negative non-target impacts of sustained control efforts
all favour an intense eradication effort, rather than a sustained
control program
Eradication of feral pigs from Santiago
Island in the Galapagos Archipelago,
Ecuador, which is the largest insular
pig removal to date
Using a combination of ground hunting
and poisoning, over 18,000 pigs were
removed during this 30-year
eradication campaign
Feral Goats
Goats were introduced to many islands by sailors in order to
establish food sources (Saint Helena, Juan Ferndandez,
Hawaii)
Island biotas mostly evolved largely without large mammalian
herbivours, and therefore where ill adapted
Introduced goats, changed the composition of plant communities,
caused extinctions and accelerated soil erosion
Goats are identified as the primary threat to 26% of threatened
insular plant species (IUCN)
They can be the sole reason or a contributing factor for island
extinctions
Fauna recovery after goat removal is often dramatic even with
long-standing goat populations (for example Pinta and Santiago
Islands Galapagos) (Campell & Donlan 2005)
The use of GIS aided hunting techniques and Judas Goats greatly
increased the efficency and reduced the costs of these
programs
Campbell & Donlan 2005
Campbell & Donlan 2005
Conservation strategies
New Zealand only has three native mammals, bats, as it has been
separated from Gondwana for at least 75million years (Atkinson
2001)
Native animals and plants are not adapted to the pressure from
mammalian predators and herbivores respectively
11 species of Moas and the large Haasts
eagle became extinct
Original restoration efforts on the smaller
islands. It was immediately realized that
mammal eradication is a key part
36 near shore islands and 16 offshore
islands have been cleared of mammals
There are also 18 ‘mainland islands’ of a total area of
28,360ha created were invasive animals and plants are
controlled in order protect natives
Atkinson 2001
Summary
Large losses of biodiversity have already occurred
on islands
Many species are endangered and threatened with
extinction
Key point for conservation is the removal of
invasive species
Better and more efficient tools are available for the
removal of mammalian predators and herbivores
There are several success stories of conservation
and restoration of island habitats
References
Biological Conservation 99 (1) issue on Introduced pest species and biodiversity conservation in New Zealand
several good articles
Whitaker RJ 1998. Island Biogeography, Ecology, Evolution, and Conservation, Oxford University Press. BOOK
Censky, E.J. et al. 1998. Over-water dispersal of lizards due to hurricanes. Nature 395:556.
Brooks TM, Mittermeier RA, Mittermeier CG, et al. Habitat loss and extinction in the hotspots of biodiversity
CONSERVATION BIOLOGY 16 (4): 909-923 2002
Spiller DA, Losos JB, Schoener TW Impact of a catastrophic hurricane on island populations SCIENCE 281
(5377): 695-697 1998
Steadman DW, Pregill GK, Burley DV PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE
UNITED STATES OF AMERICA 99 (6): 3673-3677 2002
Elliott GP, Merton DV, Jansen PW Intensive management of a critically endangered species: the kakapo
BIOLOGICAL CONSERVATION 99 (1): 121-133 2001
STEADMAN DW PREHISTORIC EXTINCTIONS OF PACIFIC ISLAND BIRDS - BIODIVERSITY MEETS
ZOOARCHAEOLOGY SCIENCE 267 (5201): 1123-1131 1995
Saunders A, Norton DA Ecological restoration at Mainland Islands in New Zealand BIOLOGICAL
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Campbell K, Donlan CJ Feral goat eradications on islands CONSERVATION BIOLOGY 19 (5): 1362-1374 2005
Blackburn & Gaston 2005 Biological invasions and the loss of birds on islands; insights into the idiosyncrasies of
extinction. Sax DF, Stachowicz JJ, Gaines SD, (eds) Species invasions; insights into ecology, evolution, and
biogeography BOOK
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QUATERNARY RESEARCH 64 (3): 451-459 2005
Traveset A, Riera N Disruption of a plant-lizard seed dispersal system and its ecological effects on a threatened
endemic plant in the Balearic Islands CONSERVATION BIOLOGY 19 (2): 421-431 2005
Cowie, R.H. 1998. Patterns of introduction of non-indigenous non-marine snails and slugs in the Hawaiian
Islands. Biodiversity and Conservation 7:349-368.
Cole, F.R., A.C. Medeiros, L.L. Loope and W.W. Zuehlke. 1992. Effects of the Argentine ant on arthropod fauna of
Hawaiian high-elevation shrubland. Ecology 13:1313-1322.
Lubin, Y.D. 1984. Changes in the native fauna of the Galapagos Islands following invasion by the little red fire ant,
Wasmannia auropunctata. Biological Journal of the Linnean Society 21:229-242.
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420-423 JUL 24 2003
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Guam's avifauna
CONSERVATION BIOLOGY 17 (5): 1350-1360 OCT 2003
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MAY 2001