Transcript Island biogeography

Island
biogeography
Peter Shaw
Introduction
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The aim of today’s lecture is to
introduce you to some of the
strange biodiversity found on
remote oceanic islands, to explain
why so many of these species are
endemic and so greatly
endangered, and to introduce of
islands system (Easter island) as a
parable of unsustainable
development.
Examples of island ecosystems
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Today I am interested in systems which are old
and highly remote.
The largest collection of these occur in the pacific:
the Hawaiian archipelago, Easter Island, Lord
Howe Island, the Galapagos...
The Indian ocean has the Mascarene islands,
Aldabra, Round island...
The Atlantic has but few - St Helena, Tristan de
Cunha.
Even the Mediterranean had its island endemics,
on Cyprus, Mallorca and others.
Colonisation
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A new volcano emerges from a mid-oceanic hotspot. Sea level changes expose a new Coral atoll.
How does live get there?
Fly or float!
Earliest colonisers usually come in on the wind seeds of plants, insects, eventually a few
exhausted birds. Spiders fly in too.
Other organisms raft in: a few plants (coconuts,
the sea bean) have seeds adapted to float in sea
water and germinate on remote beaches..
Rafting
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Is the technical name for the process by which non-flying
animals end up marooned on remote islands. Mammals do
not raft well (humans excepted), but reptiles do.
A python was found on Krakatoa within a year of its
eruption.
The Fijian iguana
Brachylophus vitiensis
is most closely related
to iguanas found in the
Carribean.
Its ancestor must have
rafted across the pacific
before the 2 Americas
collided.
What colonisers find:
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Is a pristine, predator-free system where the
problems of survival are mainly physical.
There are few or no competitors, and many
vacant ecological niches.
The processes of evolution work rapidly under
conditions like this - aberrant/odd individuals
are more likely to survive than on the
mainland, and may found an entire new
lifestyle - hence species.
Remote islands routinely contain endemic
species - the more remote the island, the
more endemics.
What you end up with:
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Is a community which has been assembled
haphazardly from a few colonising species, often
with species feeding on unusual foods or growing
in odd ways.
A general truism relates species number to island
size: for a given level of remoteness, bigger
islands have more species:
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S
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A
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S = C Az
S = Species richness
C = a constant for a given system
A = area
z = a scaling constant, typically 0.1-0.35
This means 10* area = 2* species (roughly).
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3 reasons:
 Small
Why endemics?
genetic input (the founder effect). Entire
populations have the genetic make-up of the founding
couple.
 Isolation - no connection with mainland gene pool to
dilute changes.
 Unusual selection pressures. NOT no selection
pressures, but very different to mainland life with
diseases and predators.
 Given these conditions, evolution can act rapidly.
Wallabies released on Hawaii in 1910 already have
such different colour, size and enzyme polymorphisms
to Tasmanian populations that they deserve status as a
new species.
Endemism
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Remote islands contribute to biodiversity out of all
proportion to their area, due to their endemic species.
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Even in the UK, 2 of our native mammals are island
endemics: the Skomer vole and the St Kilda vole.
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Hawaii is especially famous for endemics (91% of its
native species). The whole genus of Hibiscadelphus (6
spp. of plant) is 14 individuals in the wild.
Half the birds listed as endangered in the whole of the
US are in Hawaii.
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Features of isolated island
endemics 1: Size changes
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Birds and insects may become giant and/or
flightless. (Giant Earwig of St Helena, Dodo of
Mauritius, elephant bird of Madagascar,
Flightless rails all that used to be all over the
Pacific - now confined to Henderson island).
Mammals if present may become dwarf:
Cypress had pygmy hippos. Mallorca had an
endemic dormouse and an elephant, both
about the same size! Komodo dragons evolved
to predate pygmy elephants.
Tortoises where present become giant Galapagos and Aldabra.
Features of isolated island
endemics 2: Lifestyle changes
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The Laysan finch looks like a sparrow, but lives
like a vampire bat, sucking blood from albatrosses.
Galapagos finches have evolved to use cactus
spines as a tool.
Hawaii has a caterpillar which catches flying
insects.
In Hawaii Lobelias are giant trees.
A Seychelles tree Pisonia grandis has large sticky
flowers which catch nestling terns. The tree
benefits from their nutrients as they decay carnivorous flowers.
Features of isolated island
endemics 3: Vulnerability
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Almost all island endemics are
automatically a conservation worry
due to small geographical range.
In addition:
 They
have no fear of predation.
 They tend to be K selected - few
large offspring.
 They have no tolerance of disease.
Predation
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It is quite normal for wild birds in remote systems
to see humans as useful landing posts! This lack
of fear reflects evolutionary heritage, but is a
disaster in terms of survival.
A consistent pattern is that remote islands used to
hold giant flightless birds, until humans arrived.
 Geese
in Hawaii
 Moas in New Zealand
 Kakapos in New Zealand
 Giant owls in the bahamas.
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It seems clear that in many cases we simply ate
the species to extinction.
RIL:
BiowarfareChatham Island Black Robin
Far worse damage was done by the species
we introduced.One
Rats,
cats,
goats are
of the
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in the
the worst, but world.
deer, ferrets
and on
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andNew
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exterminated
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brought the
home
species onofPitt
and
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one entire population
the
Chatham
so by
the turn
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robin PetroicaIsland,
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home,
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century
only about
25 pairs
one! (a 2nd popn
survived
- now
100 birds
remained.
descended from
1 female)
The destruction ofRats
forest
on Little
Mangere
coupled with
swim
ashore
fromIsland,
shipwrecks,
andthe
arelow
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destructive predators of ground-nesting
caused the numbers
to decline
even further.
To prevent
extinction
birds.
Removing
rats from
the Isle
of Maythe 7
birds surviving
involved 2 tons of warfarin. Saving the dark
in 1976-77 were moved
the larger
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Island. In spreading
1980 an
heraldtopetrel
in Pitcairn
2
intensive management
tons of brodifacoum on a 65ha island.
plan was started to save the Black Robin from extinction.
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The biggest single killer of native Hawaiian birds came
from one barrel of water thrown overboard in the 1880s.
This introduced mosquitos, which vectored avian malaria.
Now the surviving endemic birds are in high, cold
mosquito-free forests.
Almost all bird life on Guam has been
wiped out by the introduction of a
Solomon-island bird eating snake
Boiga irregularis, which stowed away
with the US military. Woods are now
full of spiders webs, as there are no
birds to eat spiders or snap their webs.
Goats!
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Trochetiopsis ebenus
St Helena ebony - once
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widespread on St
Helena. 16th century
goats destroyed the
forest, and the world 
population is 2 bushes
on one remote cliff.
Are the bane of island endemic
plants. They eat anything, climb
well, and are hard to kill.
Worse, they were deliberately
released onto remote islands in
previous centuries - for food for
shipwrecked sailors.
26% of all island endemic plants in
the IUCN red data book are
mentioned as threatened by goats.
In destroying vegetation, they
endanger animals too - starving
out tortoises etc.
Ways to kill goats:
Shoot them. They soon get the hang of this one - use
a helicopter.
Poison them - paint toxins such as compound 1080
onto target foliage. (This works well at first, but as the
population falls and bushes come back this ceases to
be effective).
The Judas goat technique: release sterilised goats
onto the island, fitted with radio collars. They will
home in on the wild goats, and lead hunters to them.
Don’t stop! Pinta island (Galapagos) had 10,000
goats. These were hunted down to 3 animals, then
left. 12 years later there were 20,000 goats, albeit
very inbred.
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In Hawaii one of the threats to native forest comes
from pigs. These disturb the soil, damaging the roots
of native Metrosideros trees and allowing in
seedlings of Myrica - an alien nitrogen fixer.
Attempts to control these pigs give me 2 sharply
contrasting stories:
 Fences.
Conservation workers try to isolate pigs from
an area by putting up a fence - but a determined pig is
very hard to keep out. The most determined research
on pig-proof fences comes from the growers of illegal
Cannabis plantations, who still come along some days
to find a pig looking vague but contented, among the
squashed remains of a year’s harvest…
 Nooses: The best control measure is simply to lay
nooses at neck height along forest trails, and return
for the decaying remains every few weeks...
Easter Island (Rapanui)
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The colonisation of Easter island is one of the great
achievements of human pre-history. What happened
next is a warning.
Around AD 400 a canoe carrying
Polynesians arrived on Easter Island
after a sea voyage of at least 2000
miles. They found a wooded
volcanic island.
1000 years later a unique, complex
culture had developed. The trees
were all gone, used for boats fuel
and for moving Moai (giant
statues).
No trees = no boats
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Once the trees were gone, the islanders were isolated and
stuck. They destroyed the seabird colonies, then the bird
colonies on swimmable offshore islands, then underwent a
population crash., c. 10,000 -> 4000 in c. 50 years.
The crash phase was marked by incessant tribal warfare. Hens
were kept in heavily re-inforced stone houses, families hid in
caves, cannibalism was routine.
This phase left the island with people, chickens, a few domestic
plants - and nothing else. Wild biodiversity was all but
destroyed.
Then Europeans came - we took many slaves, introduced
smallpox, and reduced the native population to double figures.