island biogeography. macarthur and wilson concluded: 1.small islands have fewer species because...
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Island Biogeography
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MacArthur and Wilson concluded:
1. Small islands have fewer species because equilibrium species number is set at a lower level by the balance of immigration and extinction – this is a dynamic equilibrium
2. Small islands are more isolated so that after extinction, the rate of replenishment is lower for them
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Krakatau – before and after 1883 eruption
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Aerial photo of Anak Krakatau and Krakatau
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Krakatau today
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Mangrove islands off the Florida coast
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Mangrove Island Close-Up
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Dan Simberloff on MandolinNick Gotelli on Guitar
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Simberloff’s defaunation experiment on Mangroves
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Simberloff’s defaunation experiment on Mangroves
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Results from Simberloff’s Experiment
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Results from Simberloff’s Experiment pt. 2
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Island Effect
Why are there fewer species on islands than on equal sized areas of mainland?
• Differences purely to area?
• Differences due to mainland having more complex habitat?
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Bracken Fern
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Bracken Fern - Australia
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Number of species found on Bracken Fern
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Speciation on Islands
Honeyeaters
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Picture Winged Drosophila
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Picture Winged Drosophila – more than 500 species from 1 ancestor
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Picture Winged Drosophila – more than 500 species from 1 ancestor
• http://www.youtube.com/watch?v=x-r_YhATOYA&list=PL6C606070246F1C81&index=6
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Cichlid Diversity
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African Rift Lakes
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Cichlids from Lake Tanganyika (left) and Lake Malawi (right)
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Age of African Rift Lakes
• Lake Tanganyika – 12 million years old; about 250 species of cichlids; 80% endemic
• Lake Malawi – 5 million years old; about 700 species of cichlids; again 80% endemic
• Lake Victoria – 250,000 to 750,000 years old; about 400 species of cichlids – over 80% endemic
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The dodo
What makes species vulnerable to extinction?
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What makes some populations or species vulnerable to extinction?
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What makes some populations or species vulnerable to extinction?
• Rare species are more vulnerable to extinction
• Remember Rabinowitz – three factors determine rarity:
1.Geographic range
2.Width of habitat use
3.Local population size
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Passengerpigeon
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Passengerpigeon
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Allee Effect
• Some species have a minimum requirement for population size in order to successfully breed
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Characteristics that predispose species to becoming extinct
1. habitat overlap - the species occupy habitat that is desirable to humans and lose out in competition with humans for the habitat - tallgrass prairie species
2. human attention - species suffer because singled out by humans - either desired as food or fur and hunted heavily (passenger pigeon, dodo, northern elephant seal); or disliked by humans and killed as varmints (wolves, African wild dogs)
3. large home range requirements - animals needing large areas can’t find large enough areas in human dominated landscape - California condor, polar bear
4. limited adaptability and resilience - salmon return to natal stream to reproduce; won’t go elsewhere
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Habitat overlap – Konza Prairie, Kansas
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Human attention – African wild dog
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Large Home Range Requirements - California Condor
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Limited adaptability and resilience - Coho salmon
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Salmon Life Cycle
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Coho Salmon support 137 species
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Additional factors• Species in which population size is declining
• Animal species with large bodies
• Species that are not effective dispersers
• Seasonal migrants
• Species with little genetic variability
• Species with specialized niche requirements
• Species usually found in stable, pristine environments
• Species that form permanent or temporary aggregations
• Species that have not had previous contact with people
• Species closely related to other species that have gone extinct or that are endangered
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Species in population decline – barn owls
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Species with large home ranges – Polar bear
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Animals with large bodies
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Species that are not effective dispersers- Freshwater Mussels
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Seasonal migrants such as Blackpoll Warbler
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Species with little genetic variability – Madagascar fish eagle
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Species with specialized niche requirements – hummingbird flower mites
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Species usually found in stable, pristine environments
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Species that form permanent or temporary aggregations
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Species with little or no prior contact with people –
Western Australia flora
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Species related to other extinct or endangered species - Cranes
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Worldwide Endangered Species
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Endangered tree species - worldwide
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Rare and Endangered Species in Japan
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Endangered species in Canada and the US – as of 1990’s
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Threatened and Endangered Species
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ThreatenedAndEndangeredSpecies inIllinois
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Four-toed salamander – found at Green Oaks