Threats to Global Biodiversity
We wish to know:
• What is biodiversity? Why is it important?
• What are the threats to biodiversity?
• How can we estimate rates of species loss?
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What is Biodiversity?
• the variety and variability among living
organisms and the ecological complexes in
which they occur
• number and variety of species, ecological
systems, and the genetic variability they
contain.
• In its narrowest sense biodiversity refers to the
number of species on the planet
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How Many Species Exist?
• Some 1.4 to 1.8 million species are "known to
science" -- meaning that they have been
classified by a specialist
• Most experts estimate the world's species
diversity at 10 to 30 million, but that is very
approximate
• Except for land vertebrates and flowering
plants, the number of undescribed species
greatly exceeds the number described
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New Discoveries
Discovery of a new large mammal is noteworthy.
Psudoryx nghetinhensis, recently discovered
in north-central Viet Nam.
Less uncommon is the discovery that one species
is really two, such as this
Australian mountain
brushtail possum, or the
recent splitting of the
African elephant into a
savannah and forest
species.
Ichthyologists describe about 300
new fish species each year
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Number of Known, Living, Species
Among species known
to science, the
diversity of insects is
overwhelming in
number. For this
reason, most animal
species live on land,
but more phyla, the
highest level of
classification, live in
the sea.
~ 1.8 million species5
Number of Animal Species
Currently Known
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Number of Known Species of
Higher Plants
Plant diversity of the world
consists primarily of the
flowering plants
(angiosperms), which are
divided into the grasses and
other monocots, and a great
variety of dicots. Most
flowering plants live on land;
algae prevail in the sea.
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What is the real number of living
species?
10 million +
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How do we know that?
More than 70% of the species
living in a tropical forest reside
in the canopy, the uppermost
layer of the forest, and one of
the least understood
environments on Earth
The Smithsonian Tropical
Research Institute (STRI)
From Didham and Fagan
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Extinction
• Five great extinctions
• 440 mya, 370 mya, 245 mya
(Permian), 210 mya, 65 mya
(K-T)
• Followed by adaptive radiations
• The sixth extinction
• Phase 1: began 100,000 years
ago with spread of humans
• Phase 2: began 10,000 years
ago with dawn of agriculture
• Phase 3: began 250 years ago
with industrial and scientific
revolutions
http://www.actionbioscience.org/newfrontiers/eldredge2.html
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Extinction
• Definition: The end of a phyletic line without
phyletic replacement
• Five levels of extinction
•
•
•
•
•
Extinction of a species from almost all of its range
Extinction of a whole species
Extinction of groups of lower taxonomic rank
Extinction of groups of higher taxonomic rank
Mass extinction (Many groups in an epoch)
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Examples of Extinction
• Level 1
• American Bison-Estimated 50 million animals
prior to European settlement - 541 left by 1889
• White rhino - Common species in southern Africa
nearly extinct by 1894. Now stable in South
Africa, but extinct in Uganda, CAR, Zaire, Sudan
• Black rhino - Four subspecies virtually extinct
and predicted to go extinct in next few years,
other three are listed as vulnerable
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Examples of Extinction
• Level 2 - Whole species
• Irish elk - Went extinct 11,000 years ago, probable
cause was change in habitat, although cause is
debated
• Steller’s sea cow - Member of order Sirenia that
went extinct from overhunting by the 1800s.
• Level 3 - Genera and families
• Saber-toothed cats - Extinct in Pleistocene. Likely
from loss of prey, but possibly overspecialization.
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Examples of Extinctions
• Level 4-Phyletic groups
• 11,000 years ago 2/3 of America’s mammals
over 100 lbs. were lost rivaling the dinosaur
extinctions. Over 100 genera, 36 of 45 families
and 9 of 12 orders went extinct
• South America, Australia, and North America
lost 70% of megafauna, while Africa lost 20%
• Level 5 – Mass extinctions
• See previous lecture
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The Pleistocene Extinction
Climate change
Over-kill
The combination
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Modern Threats to biodiversity
Human actions now threaten species and ecosystems to
an extent rarely seen in earth history.
The Sextet of threats:
• Over-harvest
• Exotic species
• Habitat loss
• Climate change
• Pollution
• Domino effects
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Over-Exploitation
Hunting, especially
commercial hunting and
poaching, has driven many
species to extinction.
Passenger pigeon for meat,
snowy egret for fashion,
rhinos for their horns.
Bushmeat harvest is a crisis
of tropical forests today
17
Over-Exploitation
Imagine a tropical parrot
inhabiting Michigan?
The Carolina parrot, once
abundant in eastern N. America,
now extinct
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Bushmeat trade
• For the tropical forests of central and west Africa
(the Congo Basin rainforests), greatest threat to
vertebrate species is over-hunting for subsistence
and commerce
• For people living in these areas, up to 90% of total
animal protein may be derived from wild animals
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Invading species
Non-indigenous
species (invaders)
often are more
effective predators or
competitors, thereby
eliminating native
species. Island (and
lake) species may be
especially vulnerable.
Some of Victoria’ cichlids
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Michigan invaders
The gypsy moth arrived
in the U.S. in the early
1900s, and in Michigan
in the 1950s. With few
natural enemies, it
devours the leaves of
forest trees. Although
some defoliation is
tolerable, if in two
successive years and
coupled with a drought,
trees can be killed.
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Michigan invaders
There is little doubt that the sea
lamprey was primarily
responsible for decline of lake
trout in upper Great Lakes (Coble
et al. 1990). This is evidenced by
the timing of the collapse,
coincidence of wounds and scars,
simultaneous collapse in unfished
bays, and continued decline after
fishing had fallen to low levels.
Detailed analysis of catch and
effort data provided no support
for over-fishing as the cause of
declines, except in Lake Superior.
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Winning the War against
Invaders
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Global deforestation
Original tropical
forest extent was
~ 15 m km2;
today it is about
8 m km2. At
present rates of
loss, ~ 10% of
the original
tropical forests
will remain by
end of 21st
century.
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Habitat
Fragmentation
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Habitat
Fragmentation
and Extinction
Risk
Habitat loss often is
accompanied by habitat
degradation and habitat
fragmentation. Remnant
populations persist at very
low densities
Forest fragments in
Warwickshire, England,
from 400-1960
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Global Warming
Under a 2 x CO2
scenario, the
bobolink’s habitat
would shift northwards
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Domino Effects
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Species-Area
Relationships
z = slope
Studies of plant and
animal biogeography
have established a loglinear relationship
between number of
species in an area, and
areal extent. An example
for the reptiles and
amphibians for the
Caribbean is shown with
the area axis reversed, to
illustrate that reduction in
area leads to a reduction
in species.
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Estimating Rates of Species Loss
• The relationship between number of species and area
of habitat is S = c A z
• the rate of loss of tropical forest from satellite
imagery is 1-2% annually
• the resulting loss rate of species results in an overall
loss of 25 - 50% of the world’s species by 2100
• Assuming tropical forests harbor 10 million species,
this loss is 27,000/yr (and 3/hr)
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Historical vs present-day extinctions
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How much biodiversity will remain in 2100?
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hotspot designation: A terrestrial biodiversity hotspot is an area
that has at least 0.5%, or 1,500 of the worlds ca. 300,000 species
of green plants, and that has lost at least 70% of its primary
vegetation. (Current total = 34)
http://www.biodiversityhotspots.org/xp/Hotspots
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Summary
• Biodiversity refers to the number and variety of
species, of ecosystems, and of their genetic variation
• About 1.4-1.8 million species are known to science.
Because many species are undescribed, some 10-30
million species likely exist at present
• Biodiversity is threatened by the “sinister sextet”
• Habitat loss represents the single biggest threat, along
with invasive species. Over-harvest and climate
change also are significant.
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