Island biogeography

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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
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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. Small islands
harbour fewer species.
The Forsters (father son) collecting
specimens in Tahiti
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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.
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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.
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Applying the Arrhenius equation to Gleasons data
z slope
c
c intercept
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Variations in value of c
e.g. insects
plants
e.g. mammals
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Variations in the value of z
real world cases (0.26- 0.33)
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What controls the species-area curve?
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What do these have in common?
1
3
2
4
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West Indian avifaunas
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Avifaunal evidence from oceanic islands
1000
100
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MacArthur and WilsonsTheory of Equilibrium
Island Biogeography (1967)
equilibrium species number
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The effects of island size
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Species-area curve, Galapagos Islands
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Galapagos plant diversity and microclimate area
is a proxy for habitat variability
lt300 m
gt500 m
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Plant diversity in the south Pacific is the
variability controlled by habitat variation?
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The effects of island distance
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Probability of success with target distance
(metaphor)
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Dispersal probability with island distance
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Avifaunal diversity in the south Pacific the
effects of distance from PNG
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Real-world variations
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Testing the MacArthur and Wilson theory
A. Natural experiments - Krakatau/Rakata
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Bird and mammaldiversity on the remnant islands
of Krakatau vs. the biodiversity of neighbouring
islands
Rakata
remnants neighbours
Rakata
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Rakata bird colonization
McArthur Wilsons equilibrium predictions from
nearby islands 30 bird species 40 yrs to
equilibrium turnover 1 species/yr.
?
Survey dates
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Rakataplant colonization
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Rakata plant immigration and extinction
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Testing the theoryartificial experimentsI
defaunation and colonization
Small mangrove islands in the Florida keys
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Testing the theoryartificial experimentsII
colonization of artificial substrates
Fouling panels
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Variations in turnover rate at equilibrium
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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.
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Lake and bog islands
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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.

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Mountain islands
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Vacant urban lots
Vacant urban lot, Philadelphia
Crowe, L. M. 1979. Lots of weeds insular
phytogeography of vacant urban lots. J.
Biogeography 6 169-181.
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Fragmented habitat islands
1830 1882
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
1902 1950
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Urban parksbreeding birds, Madrid (Spain)