Transcript isbiogeo

Island biogeography
What controls the
number of plant and
animal species on this
island?
Does size matter?
Isolation?
Habitat variation?
Environmental history?
Island in the Bay of Fundy
Species - area relationships
Johann Reinhold Forster (1729-98) served as a botanist
with Captain Cook. After exploring the islands of the
southern Pacific he observed:
“Islands only produce a greater or
less number of species as their
circumference is more or less
extensive”.
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Small islands harbour fewer species.
The Forsters’
(father & son)
collecting specimens
in Tahiti
Species-area relationships
Arrhenius (1921) “Species and Area”
Gleason (1922) “On the relation between species and
area”. Ecology, 3.
Gleason censused the plants
in 240 1m2 plots in an
aspen wood in northern
Michigan. He found 27
species in total, with an
average of 4 species per
quadrat.
Species-area relationships
Preston (1962) “The canonical distribution of
commonewss and rarity”. Ecology, 43.
Preston introduced the ‘Arrhenius
equation’:
S = cAz
where S is number of species, A is plot
area, and c and z are constants.
Applying the Arrhenius
equation to Gleason’s data:
c
c = intercept
z = slope
Variations in value of c
e.g. insects
plants
e.g. mammals
Variations in the value of z
real
world
cases
(0.260.33)
What controls the speciesarea curve?
What do these have in
common?
1
2
3
4
West Indian avifaunas
Avifaunal evidence from
oceanic islands
1000
100
MacArthur and Wilson’s
“Theory of Equilibrium Island
Biogeography” (1967)
= equilibrium species number
The effects of island size
Species-area curve,
Galapagos Islands
Galapagos plant diversity and microclimate:
area is a proxy for habitat variability
<300 m
>500 m
Plant diversity in the south Pacific:
is the variability controlled by
habitat variation?
The effects of island
distance
Probability of success with
target distance (metaphor)
Dispersal probability with
island distance
Avifaunal
diversity
in the
south
Pacific:
the
effects
of
distance
from PNG
Real-world variations
Testing the MacArthur and
Wilson theory
A. Natural experiments - Krakatau/Rakata
Bird and
mammal
diversity on the
remnant islands
of Krakatau vs.
the biodiversity
of neighbouring
islands
Rakata
remnants
neighbours
Rakata
Rakata bird colonization
McArthur & Wilson’s
equilibrium predictions
from nearby islands:
?
30 bird species
40 yrs to equilibrium;
turnover: 1 species/yr.
Survey dates
Rakata:
plant
colonization
Rakata: plant immigration
and extinction
Testing the
theory:
artificial
experiments
I: defaunation
and
colonization
Small mangrove islands
in the Florida keys
Testing the theory:
artificial experiments
II: colonization of artificial substrates
Fouling panels
Variations
in turnover
rate at
equilibrium
Extending the theory
“Insularity is moreover a universal feature of
biogeography. Many of the principles graphically
displayed in the Galapagos Islands and other remote
archipelagos apply in lesser or greater degree to all
natural habitats”
e.g. mountain-top alpine areas; islands of
trees at the arctic treeline, urban parks,
lakes, bogs, desert oases, clearcuts, islands
of fragmented habitat, and even individual
rocks, plants, etc.
Lake and bog islands
Mountain islands
• Distribution of alpine
tundra ecosystems in
BC; an archipelago
formed by hundreds
of ± discrete islands
separated by forest
and prairie in the
neighbouring valleys.
Mountain islands
Vacant urban lots
Plant species
100
10
Vacant urban lot,
Philadelphia
100
1000
10000
Area (sq. m)
Crowe, L. M. 1979. Lots of weeds: insular phytogeography of vacant urban lots. J. Biogeography 6: 169-181.
Fragmented habitat islands
1830
1882
1902
1950
“the breakup of a large
landmass into smaller units
would necessarily lead to
the extinction or local
extermination of one or
more species and the
differential preservation of
others”
Alphonse de Candolle, 1855
True for all habitats;
e.g. Wisconsin woodlands
Urban parks:
breeding birds, Madrid (Spain)
No. of species
100
10
1
1
10
100
Area (ha)
1000
10000