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