island biogeography. macarthur and wilson concluded: 1.small islands have fewer species because...
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Island Biogeography
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
Krakatau – before and after 1883 eruption
Aerial photo of Anak Krakatau and Krakatau
Krakatau today
Mangrove islands off the Florida coast
Mangrove Island Close-Up
Dan Simberloff on MandolinNick Gotelli on Guitar
Simberloff’s defaunation experiment on Mangroves
Simberloff’s defaunation experiment on Mangroves
Results from Simberloff’s Experiment
Results from Simberloff’s Experiment pt. 2
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?
Bracken Fern
Bracken Fern - Australia
Number of species found on Bracken Fern
Speciation on Islands
Honeyeaters
Picture Winged Drosophila
Picture Winged Drosophila – more than 500 species from 1 ancestor
Picture Winged Drosophila – more than 500 species from 1 ancestor
• http://www.youtube.com/watch?v=x-r_YhATOYA&list=PL6C606070246F1C81&index=6
Cichlid Diversity
African Rift Lakes
Cichlids from Lake Tanganyika (left) and Lake Malawi (right)
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
The dodo
What makes species vulnerable to extinction?
What makes some populations or species vulnerable to extinction?
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
Passengerpigeon
Passengerpigeon
Allee Effect
• Some species have a minimum requirement for population size in order to successfully breed
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
Habitat overlap – Konza Prairie, Kansas
Human attention – African wild dog
Large Home Range Requirements - California Condor
Limited adaptability and resilience - Coho salmon
Salmon Life Cycle
Coho Salmon support 137 species
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
Species in population decline – barn owls
Species with large home ranges – Polar bear
Animals with large bodies
Species that are not effective dispersers- Freshwater Mussels
Seasonal migrants such as Blackpoll Warbler
Species with little genetic variability – Madagascar fish eagle
Species with specialized niche requirements – hummingbird flower mites
Species usually found in stable, pristine environments
Species that form permanent or temporary aggregations
Species with little or no prior contact with people –
Western Australia flora
Species related to other extinct or endangered species - Cranes
Worldwide Endangered Species
Endangered tree species - worldwide
Rare and Endangered Species in Japan
Endangered species in Canada and the US – as of 1990’s
Threatened and Endangered Species
ThreatenedAndEndangeredSpecies inIllinois
Four-toed salamander – found at Green Oaks
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