210 Islands

Island'Ecology

An#island#is#any#area#of#

suitable#habitat#

surrounded#by#an#expanse#

unsuitable#habitat.

NUNATAK'(Habitat'Island)

• Peak#surrounded#by#glaciers

• #but#not#itself#glaciated

• Merrit#Lyndon#Fernald

The#basin#and#range#province#in#Nevada#is#an#example#

of#such#a#habitat#island.

Three'types'of'Islands

Oceanic

Volcanic

Con@nental

Oceanic'Islands:##Never#connected#to#conAnent;#usually#formed#by#volcanic#acAvity#

and#isolated#from#conAnent#by#deep#ocean.

Con@nental'Shelf

Current'Sea'Level

Former'Sea'Level!

Oceanic'Island!

Sea'Floor

UnderseaVolcano

Examples'of'Oceanic'Islands

•#Iceland

•#Japan

•#AleuAans

•#Bermuda

•#Caribbean#Islands

•#Hawaiian#Islands

•#South#Pacific#Atolls

•#Et#al.

Many#Caribbean#islands#were#formed#by#volcanic#

acAvity#at#subducAon#zone.

Chilean palm (Jubaea chilensis)

Con@nental'Islands:""Formed"on"con+nent;"may"have"formerly"been"connected"to"mainland"by"land'bridge:Indonesia

Current'Sea'Level

Con@nental'Shelf

Con@nent

Submerged'Land'Bridge

Former'Sea'Level

Island

Island'flora'&'fauna

Con@nental

Biota&subset&of&con.nent

Natural&selec.on

specia.on

Island'flora'&'fauna

Oceanic

Founder'effect

Progressive&dispersal

Sophora

ENZED

Two'methods

Dispersal

Vicariance

Various'ways

Con@nental'raOs

Nunataks

Organisms'present'during'the'Cretaceous'(vicariant'groups)'

dinosaurs

Peripatus

Ra@tes

snails

Dispersal'problem

Adapta@on

For'dispersal

Not'usually'survival

Some#plants#have#

developed#seeds#or#fruits#

that#can#be#carried#in#the#

sea#without#being#

harmed.##

Dispersal'problem

Propagules

Founders!of!the!“Island!Biogeography”!

Robert'MacArthur'and'Edward'O.'Wilson'coined'the'term'“Theory'of'Island'Biogeography”'as'this'theory'aXempted'to'predict'the'number'of'species'that'would'exist'on''newly'created'island.

E.O.!Wilson!!and!Robert!MacArthur

Island'life

More'hazards

Less'area

Island'Biogeography:Species'richness'and'island'size

Small'island Less'species

Islands'and'ex@nc@on

More'likely

Small'pops

Founder'effect

Originally&adapted&for&where?

Less'richness depauperate

Island'richness

Not'@meE.O.!Wilson!!and!Robert!MacArthur

Special'equilibrium

ex@nc@on'and'coloniza@on.

Theory

species'richness'decreases'with'distance'from'mainland.

Theory

Larger'islands'should'have'more'

species

Theory

Islands'closer'to'mainland'should'have'more'species

Higher'immigra@on

ImmigraAon#rate#

decreases#as#island#

diversity#increases#

ExAncAon#increases#as#

island#diversity#increases#

Species#equilibrium#on#

islands#is#a#balance#of#

immigraAon#and#local#

exAncAon

Equilibrium#Theory#of#Island#Biogeography

Islands#further#from#

mainland#have#lower#

immigraAon#rates

More#distant#islands#have#

lower#species#diversity

Equilibrium#Theory#of#Island#Biogeography

Smaller islands have lower total populations

Probability of extinction increases with lower population

Smaller islands have lower species diversity

Theory of Island Biogeography

Biogeography'Theory'in'a'NutshellEquilibrium#number#of#

species,#but#constant#

turnover

Migra.on#slows#as#richness#increases

Ex.nc.on#increases#with#richness

Equilibrium#=#rate#of#

exAncAon,#rate#of#

colonizaAon#intersect

Coloniza.on&balances&ex.nc.on

Equilibrium"no."of"species

Island'richness

Habitats'not'area

Edge'effects

Blend'of'habitats

On&islands,&ini.ally,&more&sites&available,&some&similar&to&those&of&the&ancestors&and&some&totally&different&leading&to&

specia.on

More'isolated

Harder'to'get'to

= Less'species

Endemism

High

All'Hawaiian'birds

Higher'in'NZ

Endemism

80%&of&all&vascular&plants

70%&of&all&birds

Na.ve&species

All&na.ve&mammals

All&na.ve&rep.les&and&Amphibs

90%&of&all&fresh&water&fish

Island'Rules

Small'gets'big

Big'gets'small

Viola#spp

Island'Rules

flightless

fearless

plants'dioecious

Flightless

Ra@tes

Parrots

wrens

Shags

grasshoppers

Animal#SpecialAes.

• Flightlessness#conserved#energy#in#cold#

condiAons#and#could#flourish#in#the#absence#of#

terrestrial#mammal#predators.

• GiganAsm#is#another#adapAve#feature#

favouring#heat#retenAon.

• Melanism#also#favours#heat#retenAon#and#

energy#conservaAon.

Island'Rulesgroups'under'represented

ecologically