CONSERVATON BIOLOGYLecture07 – Spring 2015 Althoff - reference Chapters 11-12

ISLAND BIOGEOGRAPHY

Equilibrium Theories of Diversity

• Attempt to explain diversity patterns observed in natural ecosystem

• Some patterns noted:1) species richness increases dramatically from

high latitudes toward the equator2) within latitudinal belts, diversity appears to

be correlated with temperature, ecosystemproductivity, topographic heterogeneitywithin a region, and structural complexityof local habitats

3) ___________________ exhibit species impoverishment

Equilibrium Theories of Diversity…con’t

• Everywhere, higher diversity is associated with greater ecological variety

• How do we explain these patterns of diversity?1) the ultimate source of diversity is __________

(the production of new species by the splitting of evolving lineages)

2) Species _________ (i.e., go extinct)—most species that have ever existed have disappeared

3) If Speciation Extinction….Species increase If Speciation Extinction….Species decrease4) Diversity might achieve a ________________

Consider “steady-state” of species richness….

• Can examine this on a more localized level/scale (so do not think global scale for now)

• Best illustrated by examining patterns of diversity on oceanic islands

• Robert MacArthur and E.O. Wilson: EQUILIBRIUM THEORY OF ISLAND BIOGEOGRAPHY 1963 Evolution 17:373-387 (technical paper) 1967 Theory of Island Biogeography (book) ETIB

• = the number of species on an island balances regional processes governing ____________ against local processes governing ______________.

Equilibrium Theory of Island Biogeography

Number of species

Rat

e

Number of species

Rat

eImmigration

IMMIGRATION “Curve”

• As species fill an island, the ____________ of new species ______

Why? • As new species arrive, fewer are left on the

_________________• Those “left” on the mainland that haven’t

colonized have ___________________• Once all species from mainland have colonized,

immigration rate ____________

Number of species

Rat

eImmigration

Extinction

EXTINCTION “Curve”• As species fill UP the island, the ______ at

which they become _______________

Why?• Main reason: ______________________

______________ increases as species accumulate

Other FACTORS to consider...• ____________________________

• ____________________________

• ____________________________• ____________________________

___________• ____________________________

Who is most likely tocolonize?

vs.

Small vs. Large Islands

• Small islands support fewer species than larger islands…..

if _______________ from the mainland

Vs.

vs.

Near vs. Far Islands

• Islands near the mainland have more species than those farther away….

for ____________ islands

Vs.mainland

___________________________ – in general…but same result over time

ETIB

• Describes a ____________ and __________________________.

• Example, if a disaster exterminated part of an island’s biota, new colonists would—over time—restore diversity to pre-disturbance equilibrium

Test of ETIB• Simberloff and Wilson (1970)• They first counted all arthropod species

present on each of 4 small mangrove islands in Florida Bay

• Then they removed entire arthropod fauna by fumigating the islands with methyl bromide

• Islands were resampled at regular intervals for a year

Note ANote B

Note C

months

No

. o

f sp

ecie

s p

rese

nt

Simberloff and Wilson study

• Note A: islands closer to sources of colonists recovered more species faster than more distant islands

• Note B: at the end of the year, species richness had leveled off, suggesting that an equilibrium had been reached

• Note C: the new equilibrium numbers of species were similar to the numbers of species before defaunation

The Real World...

• True Islands• “Habitat” Islands

a) altitude barriersb) vegetation/habitat barriersc) disturbance

RESULT: __________________

Relevance to Conservation Biology?

• Should guide our thinking about understanding how areas might be recolonized—or efforts that need to be made to “_________” recolonization (i.e., human transport, corridors, etc.)

• Should guide our thinking about ________ ________: big vs. small, one vs. many, near vs. far, etc.