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
Examples of island ecosystems
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
Even the Mediterranean had its island endemics,
on Cyprus, Mallorca and others.
A new volcano emerges from a mid-oceanic hot-
spot. 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..
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
The Fijian iguana
is most closely related
to iguanas found in the
Its ancestor must have
rafted across the pacific
before the 2 Americas
What colonisers find:
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
What you end up with:
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:
S = C Az
S = Species richness
C = a constant for a given system
A = area
z = a scaling constant, typically 0.1-0.35
A This means 10* area = 2* species (roughly).
Small genetic input (the founder effect). Entire
populations have the genetic make-up of the founding
Isolation - no connection with mainland gene pool to
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
Remote islands contribute to biodiversity out of all
proportion to their area, due to their endemic species.
Even in the UK, 2 of our native mammals are island
endemics: the Skomer vole and the St Kilda vole.
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.
Features of isolated island
endemics 1: Size changes
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
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
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 -
Features of isolated island
endemics 3: Vulnerability
Almost all island endemics are
automatically a conservation worry
due to small geographical range.
They have no fear of predation.
They tend to be K selected - few
They have no tolerance of disease.
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.
It seems clear that in many cases we simply ate
the species to extinction.
Chatham Island Black Robin
Far worse damage was done by the species
One of the rarest birds in goats are
we introduced. Rats, cats, pigs andthe
deer, ferrets and possums are
the worst, but world. It once lived on Pitt,
also causing damage in New Zealand.
Mangere and Little Mangere
Islands. Cats exterminated home
One lighthouse keeper’s cat brought the
species on Pitt and Mangere
one entire population of the Chatham island
robin PetroicaIsland, so by the turn of the by
traversi home, dead, one
century only about 25 100
one! (a 2nd popn survived - nowpairs birds
descended from 1 female)
The destruction of forest on Little Mangere Island, coupled with the low
Rats swim ashore from shipwrecks, and are
breeding rate, destructive predators of ground-nesting
birds. Removing rats To prevent extinction the
caused the numbers to decline even further. from the Isle of May 7
birds surviving involved 2 tons of warfarin. Saving the dark
herald petrel in Pitcairn Island. In 1980 an
in 1976-77 were moved to the larger Mangereinvolved spreading 2
intensive management of brodifacoum on a 65ha island.
plan was started to save the Black Robin from extinction.
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
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.
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
Trochetiopsis ebenus shipwrecked sailors.
St Helena ebony - once
widespread on St
26% of all island endemic plants in
Helena. 16th century the IUCN red data book are
goats destroyed the mentioned as threatened by goats.
forest, and the world In destroying vegetation, they
population is 2 bushes
endanger animals too - starving
on one remote cliff.
out tortoises etc.
Ways to kill goats:
Shoot them. They soon get the hang of this one - use
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
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
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
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)
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
1000 years later a unique, complex
culture had developed. The trees
were all gone, used for boats fuel
and for moving Moai (giant
No trees = no boats
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
Then Europeans came - we took many slaves, introduced
smallpox, and reduced the native population to double figures.