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