Island BiogeographyIsland Biogeography

Island BiogeographyIsland Biogeography

o Colonization - arrivalColonization - arrival– floatfloat– flyfly– swimswim– be carriedbe carried– wind (seeds, spores)wind (seeds, spores)

Surtsey (1963)Surtsey (1963)

25 miles from Iceland25 miles from Iceland QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.

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Plant colonization - SurtseyPlant colonization - Surtsey

Krakatau (1833)Krakatau (1833)

Colonization - KrakatauColonization - Krakatau

anak Krakatau

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Characteristics of Island Characteristics of Island SpeciesSpecies

o Good dispersal abilityGood dispersal ability

o Flock loving animalsFlock loving animals

o Prefer fresh water, mangroves, Prefer fresh water, mangroves, secondary forest on the mainlandsecondary forest on the mainland

o High ecological flexibilityHigh ecological flexibility

Maquire Maquire (Ecol. Monog. 33:161-185)(Ecol. Monog. 33:161-185)

o Placed bowls of nutrient solution at various Placed bowls of nutrient solution at various distances and heights from a pond.distances and heights from a pond.

o Some bowls increased, then decreased in one Some bowls increased, then decreased in one species as others moved in. species as others moved in.

o The number of The number of newnew species/unit time species/unit time decreased with time. They finally reached an decreased with time. They finally reached an equilibrium state.equilibrium state.

o Different bowls had different species Different bowls had different species assemblages.assemblages.

MacArthur and WilsonMacArthur and Wilson

As species As species , there are more , there are more species which could go extinct. species which could go extinct.

As species As species , the , the probablility of arrival of probablility of arrival of new species new species

EE

II

# of Species is a dynamic # of Species is a dynamic equilibriumequilibrium

High

LowNumber of species on island

Rat

e o

f im

mig

rati

on

or

exti

nct

ion

Enclosing the “island”Enclosing the “island”

Simberloff - equilibriumSimberloff - equilibrium

Size relationshipsSize relationships

o If same If same distance from distance from mainland, mainland, immigration immigration should be the should be the samesame

E large

I

E small

Number of Species

Rate

S S

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Small Islands - high turnover Small Islands - high turnover raterate

o Microtus pennsylvanicusMicrotus pennsylvanicus (meadow vole) (meadow vole)

o Clethrionomys gapperi Clethrionomys gapperi (red-backed vole)(red-backed vole)

o 12 red-backed voles introduced to Rock Island12 red-backed voles introduced to Rock Island

– rapidly displaced meadow vole in small rapidly displaced meadow vole in small woodlandwoodland

– population never > 30population never > 30

– went extinct in 3 yearswent extinct in 3 years

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Red backed voleRed backed vole

Meadow voleMeadow vole

100

1 10 100 1,000 10,000 100,000

Area (square miles)

Nu

mb

er o

f am

ph

ibia

n a

nd

rep

tile

sp

ecie

s

10

SABA MONTSERRAT CUBA

Hispaniola

Puerto Rico

Jamaica

Cuba

Montserrat

Saba

Redonda

Inland IslandsInland Islands

Mountain tops in New GuineaMountain tops in New Guinea

Species/Area relationshipsSpecies/Area relationships

Slope of regression line relating S to AS = CAz

Area

Constant, gives number of species when A = 1

# of species

For most islands z falls between .24-.34

For areas of the mainland z is between .12-.17

Species/Area CurveSpecies/Area Curve

Nonequilibrium theoryNonequilibrium theory

o Suggested by Suggested by LawlorLawlor

o Non-flying Non-flying mammals mammals have not come have not come to equilibrium to equilibrium on oceanic on oceanic islandsislands

Text fig. 24.21Text fig. 24.21

Relationship to DistanceRelationship to Distance

o Extinction is not Extinction is not likely to be likely to be affected by affected by remotenessremoteness

I near

I farE

S S

Rate

100

50

25

12.5

6.25

0 2,000 4,000 6,000 8,000 10,000

Distance from New Guinea (kilometers)

Nu

mb

er o

f sp

ecie

s (p

erc

enta

ge

of

sam

ple

stu

die

d)

NEW GUINEA

MacArthur-Wilson model MacArthur-Wilson model predictionspredictions

o Number of species should remain Number of species should remain constant over timeconstant over time

o Some species should become extinct over Some species should become extinct over timetime

o Extinctions balanced by immigrationsExtinctions balanced by immigrationso Turnover rate of species should vary with Turnover rate of species should vary with

island area and distance from a source of island area and distance from a source of immigrantsimmigrants

Assembly rulesAssembly rules

o Worked out by Jared DiamondWorked out by Jared Diamond

o Three sets of rules determining the Three sets of rules determining the species mix on an islandspecies mix on an island

– Incidence functionsIncidence functions

– Compatibility rulesCompatibility rules

– Combination rulesCombination rules

Incidence FunctionsIncidence Functions

o Incidence functions place species into 3 Incidence functions place species into 3 groups:groups:

– Species only on species rich islands. Species only on species rich islands.

– Tramps - on species rich islands and Tramps - on species rich islands and with lower probability on species poor with lower probability on species poor islands.islands.

– Super tramps - only on species poor Super tramps - only on species poor islands.islands.

Compatibility rulesCompatibility rules

o Built from mutually exclusive ranges of Built from mutually exclusive ranges of pairs of species.pairs of species.

o Certain closely related species cannot Certain closely related species cannot co-exist.co-exist.

Combination rulesCombination ruleso Based on diffuse competition rather than Based on diffuse competition rather than

direct.direct.o Prevents certain groups of species from co-Prevents certain groups of species from co-

existing.existing.o Calculates the probability of a given Calculates the probability of a given

combination being found together on an combination being found together on an island of a given size island of a given size

o The only stochastic part is the order of The only stochastic part is the order of arrival of the first colonists. arrival of the first colonists.

Example: CubaExample: Cuba

Banana quitBanana quit