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. Species - area relationships. - PowerPoint PPT PresentationTRANSCRIPT
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Island biogeography
Island in the Bay of Fundy
What controls the number of plant and animal species on this island?
Does size matter?Isolation?Habitat variation?Environmental history?
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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.
QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.
The Forsters’ (father & son)
collecting specimens in Tahiti
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Species-area relationshipsArrhenius (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 relationshipsPreston (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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c
Applying the Arrhenius equation to Gleason’s
data:
z = slope
c = intercept
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Variations in value of ce.g. insects
e.g. mammals
plants
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Variations in the value of z
realworldcases(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
23
4
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West Indian avifaunas
10010 0001 000 0001 000100 000Area (km )21020406010020080Jamaica
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Avifaunal evidence from oceanic islands
100
1000
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MacArthur and Wilson’s“Theory 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
<300 m >500 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 mammal
diversity on the remnant
islands of Krakatau vs.
the biodiversity of
neighbouring islands
remnantsneighbours
Rakata
Rakata
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Rakata bird colonizationMcArthur & Wilson’s equilibrium predictions from nearby islands:
30 bird species 40 yrs to equilibrium;turnover: 1 species/yr.
?
Survey dates
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Rakata:plant
colonization
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Rakata: plant immigration and extinction
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Testing the theory:artificial
experimentsI:
defaunation and
colonization Small mangrove islands in the Florida keys
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Testing the theory:artificial experiments
II: colonization of artificial substratesFouling 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
10
100
100 1000 10000Area (sq. m)
Plant species
Crowe, L. M. 1979. Lots of weeds: insular phytogeography of vacant urban lots. J. Biogeography 6: 169-181.
Vacant urban lot,Philadelphia
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Fragmented habitat islands
“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
1830 1882
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Urban parks:breeding birds, Madrid (Spain)
1
10
100
1 10 100 1000 10000Area (ha)
No. of species