island biogeography and habitat loss...island biogeography and habitat loss 1. habitat loss and...

Island Biogeography and Habitat Loss

1. Habitat loss and fragmentation2. Lessons from islands• Effects of patch area and shape on species richness • Macarthur-Wilson equilibrium theory

of island biogeography

300 years

Old Growth Forest

Aboveground Woody Biomass

log(S) = log(c) + z log(A)

AREA effects: Species – Area Curves

log(c)

z

S = c Az

S = # of speciesA = areaz and c are fitted constants

Boreal mountain patches

z ≈ 0.15 – 0.35

S

A

50%

90%

Data from habitat patches is similar to data from islands

10|2 Rule for z = 0.25

As Area ↓ Wide ranging species ↓As Area ↓ Population sizes ↓

Patch area AND shape affect species richness through edge effects

As A decreases, edge:interior ratio increases

Minimum edge:interior ratio

All edge

Det

ecti

on

or

occ

urr

ence

As area increases, occurrence decreases for the edge species

As area increases, occurrence increases for ground-nesting interior species

Edge species

Interior species

Worm-eating warblerOvenbird

American robinGray catbird

Figure 19.18

Equilibrium Theory of Island Biogeography

Theory

Rat

e

Number of species on island (S)

Island size and connectivity determine species richnessMacArthur and Wilson 1963

S is a balance between immigration of new species and extinction of resident species

Equilibrium Theory of Island Biogeography

Theory

Rat

e

Number of species on island (S)

I

P = Size of source pool

Equilibrium Theory of Island Biogeography

Theory

Rat

e

Number of species on island (S)

IE

PSize of source pool

Equilibrium Theory of Island Biogeography

Theory

Rat

e

Number of species on island (S)

S^

^T

IE

PSize of source pool

# of species present is a balance between immigration of new spp. and extinction of resident spp.; species composition continually changing, but total number of species constant

Data for birds in Solomon Islands

Number of species, S

Rat

e o

f im

mig

rati

on

or

exti

nct

ion

(sp

ecie

s/yr

)

Shapes of I and E curves:

r/K selected species

The Distance Effect: Theory

Number of species on island (S)

Rat

e

In

If

E

PSnSf

Sou

rce

po

ol

n = nearf = far

The Distance Effect: DataD

isp

ers

al

Distance from sourceOdum 1959; Wolfenbarger 1976

The Area Effect: Theory

Number of species on island (S)

Rat

e

IEs

PSLSs

Sou

rce

po

ol

L = larges = small

EL

DATA: S-A curves

The Area Effect: Data

MW Equilibrium

Model of Island

Biogeography

combined distance-area

effects

Target effect= immigration

is higher on large islands

Rescue effect = extinction is lower on near

islands

Modifying Effects for MW model

X

X

X

X

2005

2006

2007

Simberloff’s mangrove island experiments“Defaunation”

Island E9

Pre: 29 speciesPost: 24 species

Overlap: 8 species