Download Biodiversity

How many tigers
does the world need?
Human Population Growth
CB 52.22
CB 55.2
Genetic Diversity
Biodiversity- number of
species within an area
Ecosystem Diversity
Ecosystems on Earth
CB
50.19
Have we overstated the tropical
biodiversity crisis?
William F. Laurance
Trends in Ecology & Evolution
Vol. 22: 65-70 February 2007
Are we on the verge of a massive die-off of
tropical species?
Changes in Extinctions and Diversity
Are we on the verge of a massive die-off of
tropical species?
Increased
rural density
leads to
decreased
forest.
This is
because rural
slash-andburn farmers
cause most
forest loss.
The good news?
About 21–24% of species in the Asian tropics
and 16–35% of species in the African tropics
are threatened with possible extinction.
Rural
populations
are expected
to decline.
Substantial areas of agricultural land are likely
to be abandoned, because the population
growth rates of many developing nations are
slowing and because of increasing
urbanization.
This could enable significant forest
regeneration, which could help buffer species
losses from deforestation.
CB 55.21
Human vs Natural Disturbances
Extinction rates are likely to be higher in
biodiversity hotspots
CB 55.17
Terrestrial Biodiversity Hotspots
the 16 hotspots that sustain tropical forest
have already lost, on average, 90% of their
forest cover
Rainforest clear cutting
CB 55.15
CB 55.13
Not all habitats are equal
A third to a half of all
old-growth species avoid
younger (<30-year-old)
regrowth.
In many tropical
regions, future
pressures on
forests will be
determined more
strongly by
industrial drivers,
globalization and
macroeconomic
forces than by
local population
density.
Rural
populations
are expected
to decline,
but
increased
urban
population
will demand
more
resources.
The
precautionary
principle
maintains that
one should err
on the side of
caution in
conservation
matters.
We need to evaluate critically the degree to
which regenerating and degraded habitats,
which are increasing dramatically at the
expense of old-growth forests, can sustain
tropical biodiversity
Why are species going extinct?
2%
36%
39%
Species
introductions
Hunting
Habitat
Destruction
Other
23%
Nearly Extinct
Species:
maybe only 100
individuals exist
CB 55.3
Extinction Vortex
Attwater Prairie
Chicken
As population
declined, genetic
diversity declined
CB 55.10
Attwater Prairie
Chicken
Individuals brought
from other
populations
increased
reproduction and
population
CB 55.10
Why are species going extinct?
2%
36%
39%
Species
introductions
Hunting
Habitat
Destruction
Other
23%
Ecosystem
Fragmentation
Habitat loss and fragmentation has been
extensive in the US due to human modification
of the environment
Many human tragedies have been a boon for
native animal species:
http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=15362
Science v. 269 pg. 304 7/21/1995
Korean DMZ: Among the species making their
homes in the DMZ are endangered Asian cranes,
black-faced spoonbills, angora goats, Amur leopards,
and even bears.
http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=15362
Savanah River nuclear site in Georgia:
forest remnant
Why are species going extinct?
2%
36%
39%
Species
introductions
Hunting
Habitat
Destruction
Other
23%
Invasive species
can disrupt an
ecosystem by
outcompeting
native species for
resources
CB 55.6
Nile Perch (Lates niloticus)
• Introduced to Lake Victoria in 1954 to
increase fish yield
• Caused extinction of 200+ endemic fish
species through predation, and competition
• Fish caused indirect increased erosion on
land, causing higher nutrient levels in the
lake.
Water Hyacinth (Eichhornia crassipes)
• Introduced as ornamental plant around the world
• Now in 50 countries on 5 continents including US
• In California it replaced the native pennywort
(Hydrocotyle umbellata) which occupies a similar
habitat, leading to a marked decrease in invertebrate
communities
• Limits water transport, reduces oxygen and light
levels in the water
Zebra mussel (Dreissena polymorpha)
• Spread from its native range in the Baltic
Sea via ballast water
• Spreads in Europe and North America
• Kills native molluscs, changes ecosystems,
and damages infrastructure
• Estimated annual damage in US $3 billion
The brown tree snake
(Boiga irregularis)
• Its native in Australia and was introduced to Guam
accidentally in the 1950’s
• Overall responsible for the extinction of 3 out of 4
seabirds; 9 out of 13 forest birds; 3-5 out 12 reptile
species on the Island of Guam.
• This snake caused the extirpation or serious
reduction of most of the island's 25 resident bird
species on the main island of Guam.
How Many Invasive Species Are There in
Texas?
 67 terrestrial plants
 12 aquatic/wetland plants
 10 mammals
 4 birds
 7 fishes
 11 insects
 11 mollusks and crustaceans
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Hydrilla verticillata
Aquatic invader covering nearly 100,000 surface
acres of water in Texas.
Spreads rapidly, in one Texas lake it covered 23 acres
in 1999 but over 200 in 2000.
Depletes water of oxygen and blocks sunlight killing
off many native plants and animal species.
Hydrilla on Longhorn dam over Town Lake
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Why are species going extinct?
2%
36%
39%
Species
introductions
Hunting
Habitat
Destruction
Other
23%
For Th, 6/26, please bring a laptop if possible.
How many tigers
does the world need?