Island Biogeography - University of Windsor

Loses of biodiversity
Natural Extinctions
• Surprisingly, we know very little about natural
• In the past, known only from fossil records
• Physical evidence of cause rarely preserved
• Cause and Effect hard to establish
• Post hoc ergo propter hoc danger
• Even if cause established, what’s the
• Many islands are ‘newly’ colonized by people
Natural Extinctions
• Habitat Disruption
– Volcanic Eruptions
– Asteroid Impacts
• Habitat Modification
– Climate Change
• Continental Drift
– Mountain-Building
– Sea Level Change
• “Exotic” Species
Island biodiversity
• Islands have a very high level of endemism,
contributing disproportionably to their size to
• 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
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. Winds 90 knots surge 5m
• larger bodied animals (ie. lizards) more resistant to immediate
impact of moderate disturbance (hurricane)
• small-bodied spiders responded more quickly after the
• extinction (or more properly extirpation) from islands was
related to population size only when disturbance was
• Recovery rates related to dispersal ability.
Impact of Hurricane Lilly on Islands in the
Hurricane Lili hit
these islands
with a 5m storm
surge and
90knot winds
(Spiller 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 – prior to humans
(Steadmann 1995)
Natural dispersal does still occur
• Biodiversity on islands is the product of
immigration, extinction, and in situ speciation (in
some cases).
• 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.
Disturbance and Dispersal
• 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
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 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).
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)
Prehistoric spread of humans
When Colonized
4,000 years
~ 28,000 years ago
years ago
~ 4,000 years ago
~ 3,500 years ago
~ 1,500 years ago
Human-Caused Extinction
• Excessive Predation (Food, fur, collecting,
pest eradication, etc.)
• Habitat Destruction –
– Losses or changes in food availability
• Destruction of keystone species
• Introduction of Exotic Species
– Competitors
– Predators
– Diseases
Prehistoric island 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
Prehistoric island 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
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
Tonganese Island depending on
foraging height and food type
Frugivores declined very sharp with
a negative effect on tree
Ground feeders (7-0) became
extinct caused by human and
non-native mammal predation
Steadman 1995)
Endemic Island Biota Extinction or
• Many of Hawaii’s honeycreeper spp. are extinct
• More than 10% of Hawaii's
diverse plant species are
extinct - another 40% are
Endemic Island Biota Extinction or
• 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).
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
• The species most likely to become extinct were large bodied,
flightless, ground-dwelling or ground-nesting
Direct habitat destruction
• Direct habitat destruction associated with cutting or burning
of forests for agriculture, construction, and wood extraction.
• 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.
Species Introductions
• 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.
Species Introductions
• 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).
• 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 (either primary or
secondary) were precipitated by loss of food
resources associated with destruction of
habitat or introduced species.
• Rats (R. exulans) may have caused
invertebrate declines which reduced food
supplies for the extinct birds Aptornis and
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 of
carnivourous mammals (Traveset & Riera 2005)
• The lizard consume 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 islands without the lizard the shrub only
recruits underneath the parent plant
• This is the likeliest reason why this plant is
The brown tree snake
(Boiga irregularis)
• It’s native in Australia and was introduced accidentally in the
• 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
• 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.
• 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
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
Conservation Case Study: New Zealand
New Zealand only has three native mammals, bats, as it
has been separated from Gondwana for at least 75 million
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
New Zealand
• colonized by humans only 1000-800 years ago. Endemism is
high on oceanic islands in this group, though diversity is lower
than on the larger (continental) islands.
• This tremendous diversity has resulted from the islands' range
of climates (subtropical to sub-antarctic), 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
• 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.
Atkinson 2001
Vertebrate invaders in New Zealand
New Zealand: Conservation Strategies
• 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
New Zealand: Conservation
• For example, the black robin (Petroica traversi)
numbered only 9 individuals in 1975; the 7 (2
breeding pairs) birds were captured in 19761977 and moved from its degraded habitat on
Little Mangere Island to Mangere and later to
South East Islands.
New Zealand: Conservation
• The species was on the brink of extinction (1015 individuals) for 8 more years before eggs
were cross-fostered with Chatham Island Tits
(closely related), which increased production
of black robin fledglings. In 1992 the species
totalled 120 birds.
New Zealand: Conservation
• Helicopter-dispersed rodenticide eliminated rats from Red
Mercury Island after the 20 resident reptile 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.
New Zealand: Conservation
• Captive breeding programs are presently
helping two endangered flightless birds: the
gallinule Takahe (Porphyrio mantelli), of which
150 individuals remain (Clout and Craig 1994)
and the nocturnal parrot Kakapo (Strigops
habroptilus), of which 50 individuals
remain. These species were both thought
extinct before small populations were found.
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 introduced by the
Polynesians and European introduce 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
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
Due to high mortality of adults 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 1990
Large losses of biodiversity have already occurred
on islands
Many species are endangered and threatened with
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
North America
• Steller’s Sea Cow
– Cold-Water Relative of Manatee
– Extinct 1768
• Great Auk
– Flightless, Penguin-like North Atlantic Bird
– The Original “Penguin”
– Nice Example of Convergent Evolution
– Extinct 1844
The Passenger Pigeon
• May once have been the most numerous bird
on the planet
• Estimated 5 billion
• Made up 30-40% of all North American birds
• Flocks 1 mile wide, 300 miles long
• Evolved to travel and breed en masse
• Protection against most predators
Humans and the Passenger
• Unlike other predators, humans exploited the
mass flocks of the passenger pigeon
• Netting, mass shooting
• Railroads shipped pigeons to market, created
• Declines noted by 1860
• Species could probably have survived even
this predation, except….
Extinction of the Passenger
Pigeons were hunted in nesting sites
Hunters used telegraph to learn of colonies
Conservation laws too little, too late
Last wild pigeons shot Wisconsin, 1899 and
Ohio, 1900
Extinction of the Passenger
• Scattered birds could not breed
• Captive breeding attempts failed
• Last bird died in Cincinnati Zoo, September
14, 1914, 1 PM
• The only extinction we can time to the minute
The Heath
The Heath Hen
• Eastern race of the prairie chicken
• Once ranged from Maine to Virginia
• Hunting caused visible decline by 1800, steep
by 1830
• By 1870, restricted to Martha’s Vineyard,
• By 1906, only 50 left
• 1907, Sanctuary established
The Heath Hen – Back From
the Brink?
• 1907: Sanctuary established for last 50 birds
• By 1915, number had grown to 2000
• Species had been rescued?
The Heath Hen – Over the
• 1907-1915: Heath hen had grown from 50 to
2000 birds
• 1916: Fire destroyed most of refuge
• Harsh winter and influx of hawks further
damaged species
• Flock attacked by disease from domestic
• By 1927, only 13 left, mostly male
• Last bird seen alive, 1932
Carolina Parakeet
• Only Parrot Native to U.S.
• Once ranged from Virginia to Texas
• Adapted readily to agriculture and became
regarded as a pest
• Widely hunted
• Rare by 1880’s
• Last Seen in Florida about 1920
American Chestnut
• American Chestnut was once a
major food crop and lumber
• Accounted for half the value of
eastern timber
• Devastated by blight 1904-30
• Isolated trees and viable roots
still survive
• Research on blight immunization
• Even if blight cured, other trees
have filled ecological niche
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
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
ZOOARCHAEOLOGY SCIENCE 267 (5201): 1123-1131 1995
Saunders A, Norton DA Ecological restoration at Mainland Islands in New Zealand BIOLOGICAL
CONSERVATION 99 (1): 109-119 2001
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
Fall PL Vegetation change in the coastal-lowland rainforest at Avai'o'vuna Swamp, Vava'u, Kingdom of Tonga
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.
Brook BW, Sodhi NS, Ng PKL Catastrophic extinctions follow deforestation in Singapore NATURE 424 (6947):
420-423 JUL 24 2003
Wiles GJ, Bart J, Beck RE, et al.Impacts of the brown tree snake: Patterns of decline and species persistence in
Guam's avifauna
CONSERVATION BIOLOGY 17 (5): 1350-1360 OCT 2003
Atkinson IAEIntroduced mammals and models for restoration BIOLOGICAL CONSERVATION 99 (1): 81-96
MAY 2001