Island Biogeography and Habitat Loss 1. Habitat loss and fragmentation 2. Lessons from islands • Effects of patch area and shape on species richness • Macarthur-Wilson equilibrium theory of island biogeography Old Growth Forest

300 years

Aboveground Woody Biomass AREA effects: Species – Area Curves

z

S = c Az log(c) S = # of species A = area z and c are fitted constants log(S) = log(c) + z log(A) Data from habitat patches is similar to data from islands

Boreal mountain patches

z ≈ 0.15 – 0.35

50%

S

90%

A

10|2 Rule for z = 0.25 As Area ↓ Population sizes ↓ As Area ↓ Wide ranging species ↓ Patch area AND shape affect species richness through edge effects

As A decreases, edge:interior ratio increases

Minimum All edge edge:interior ratio Detection or occurrence Worm As As areaincreases, occurrenceincreases for ground Gray catbird - eatingwarbler As As areaincreases, occurrencedecreases for the edge species Edge species Interior species Americanrobin Ovenbird - nestinginterior species Figure 19.18 Equilibrium Theory of Island Biogeography Island size and connectivity determine species richness MacArthur and Wilson 1963

Theory Rate

Number of species on island (S)

S is a balance between immigration of new species and extinction of resident species Equilibrium Theory of Island Biogeography

I

Theory Rate

P = Size of source pool

Number of species on island (S) Equilibrium Theory of Island Biogeography

I

Theory E Rate

P Size of source pool Number of species on island (S) Equilibrium Theory of Island Biogeography

I Theory E

^

Rate T

^ P S Size of source pool Number of species on island (S)

# 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 )

yr Data for birds in Solomon Islands

Shapes of I and E curves:

r/K selected

species Rate of immigration or extinction (species/ extinction or immigration of Rate Number of species, S The Distance Effect: Theory

I n E

If

Rate Source pool Source

Sf Sn P Number of species on island (S)

n = near f = far

The Distance Effect: Data Dispersal

Distance from source Odum 1959; Wolfenbarger 1976 The Area Effect: Theory

I Es

EL

Rate Source pool Source

Ss SL P Number of species on island (S)

L = large DATA: S-A curves s = small The Area Effect: Data MW Equilibrium Model of Island Biogeography

combined distance-area effects Modifying Effects for MW model

Target effect X = immigration is higher on large islands

Rescue effect X 2005 = extinction is lower on near X 2006 islands X 2007 Simberloff’s mangrove island experiments “Defaunation” Island E9

Pre: 29 species Post: 24 species

Overlap: 8 species