Transcript Extinction and Island Biogeography

Value of genetic diversity
• Why are genes valuable? Or
• What kind of value do genes have?
Value of genetic diversity
• Genes have instrumental value – they are
valuable for what they do
Grassy Stunt Virus in Rice
Oryza nivara
Native habitat of O. nivara in
Uttara Kannada, India and Distribution
Extinction
Current Extinctions
Rates of Extinction
Expected from Fossil Record:
• 4 species a year go extinct from 10 million
living species
• 1 mammal species (out of about 4000
living) extinct every 400 years
• 1 bird species (out of just over 9000 living)
extinct every 200 years
• 40 plant species extinct in 400 years (out of
250,000 living)
Rates of Extinction
Rates of extinction on mainland areas since
1600
• mammals 1.6% extinct (62 of 4000)
• birds 1.3% extinct (117 of 9000)
• vascular plants 0.3% extinct (596 of
250,000)
Alwyn Gentry and friends in the field
Centinela Ridge, Ecuador
ridge is located in box on map
Estimating Loss of Unknown Species
• Based on the Theory of Island Biogeography from
which we know that larger areas support more
species and from which we know that if we reduce
the size of an island, we lose species - this
knowledge is described by the species-area
equation
•
S = cAz
• where S = species number, A = area, c is a
constant that varies depending on the type of
species and habitat in question, z is the slope of
the curve
Extinct Australian Megafauna
Some Extinct
And still living
Pleistocene
Megafauna
Species in top half
came from South
America to North
America; species in
bottom half from
N. America to S.
America
Extinct American mega-bird
Recent Pleistocene Extinctions
What is habitat fragmentation?
Habitat Fragmentation
• Fragmentation is the breakdown of a habitat
or ecosystem into smaller patches of that
habitat or ecosystem that now are isolated
from each other
Habitat
Fragmentation
Island Biogeography
Charles Darwin and Alfred Russel Wallace
The Galapagos
Galapagos Tortoise
Galapagos Mockingbirds
Galapagos Mockingbirds collected
by Darwin
Malay Archipelago
Beetles and Moths Collected by
A.R. Wallace
Butterflies from Malay Archipelago
Sphingid Butterfly Diversity Malay
Archipelago
Island
Habitats in
Baltic Sea
Reptile and Amphibian Species Area Curve
for Caribbean Islands
Habitat Islands
In the Great Basin
Bird Species
Mammal Species
Species Area Curve
S=
z
cA
where:
S = number of species
A = area of island
c = constant for habitat type - forest, desert,
grassland, etc.
z = slope of curve
Ant species
On New
Guinea and
Nearby
Islands
Real Slopes for Species-Area Curves
Oceanic islands
birds - New Guinea islands
beetles - West Indies
land plants - Channel Islands
z=0.22
z=0.34
z=0.37
Habitat islands
birds - Andes paramo
birds - mtns of Great Basin
mammals - mtns of Great Basin
inverts -caves in West Virginia
z=0.29
z=0.165
z=0.326
z=0.72
Robert MacArthur and E.O. Wilson originators of the Equilibrium Theory of
Island Biogeography
Ruffed Grouse by Audubon
Ruffed Grouse – male mating display
Apostle Islands – Lake Superior
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