Download ENVI 30 Environmental Issues

Biodiversity – Definitions and Assessment
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B.
Estimates of Biodiversity
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Described species ~ 1.8 million
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Insects > 1,000,000 species
Plants > 290,000 species
Probably an underestimate
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Only ~5000 species of bacteria
Less conspicuous species studied less often
Estimates range from 5 – 30 million
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Around 300 new species described each day
Average estimate ~ 17.5 million
Splitting of taxa more common than lumping
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Tendency to increase number of described species
Cryptic species
Biodiversity – Definitions and Assessment
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C.
Estimates of Extinction Rates
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Geological history
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Periods of extinction followed by periods of rapid speciation
(every ~ 26 million years)
How do we estimate rates of extinction??
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1.
Problems
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b.
c.
d.
Difficult to know when a species is extinct
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Ex – Coelacanth, ivory billed woodpecker, giant lemur
Species distributed unevenly (patchy distribution)
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Species affected unevenly by habitat loss
Extinctions may not happen immediately
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Short-lived species show effects rapidly
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Long-lived species may appear to be unaffected for long
periods of time
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“Biologically extinct” – Populations not self-sustaining
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“Living dead” - Janzen
Uncertainty about number of species in an area
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Wilson – “No precise estimate can be made of the
numbers of species being extinguished in the rain forests
or in other major habitats, for the simple reason that we do
not know the numbers of species originally present”
Biodiversity – Definitions and Assessment
I.
C.
Estimates of Extinction Rates
2.
Estimation Methods
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a.
b.
c.
d.
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Area-species relationship (MacArthur & Wilson)
Estimate biodiversity for a small area
Extrapolate estimate to area of habitat
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Species ~ Area0.25 (0.15-0.35)
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Increase area 10X  Increase species 2X
Estimate rate at which ecosystem area is being reduced
Calculate extinction rate based on predicted reduction
in species richness from reduction in habitat area
Current estimate ~ 17,500 species year-1
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1 out of every 1000 species on Earth each year
“Background” rate from fossil record
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1 out of every 1-10 million species on Earth each
year
Biodiversity – Definitions and Assessment
I.
C.
Estimates of Extinction Rates
2.
Estimation Methods
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a.
b.
c.
d.
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Area-species relationship (MacArthur & Wilson)
Estimate biodiversity for a small area
Extrapolate estimate to area of habitat
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Species ~ Area0.25 (0.15-0.35)
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Increase area 10X  Increase species 2X
Estimate rate at which ecosystem area is being reduced
Calculate extinction rate based on predicted reduction
in species richness from reduction in habitat area
Current estimates ~ 17,500 species year-1
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1 out of every 1000 species on Earth each year
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Myers – 40,000 year-1
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Lomborg – 1033 documented from 1600 – 1998
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The Skeptical Environmentalist
“Background” rate from fossil record
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1 out of every 1-10 million species year-1
Biodiversity – Definitions and Assessment
I.
C.
Estimates of Extinction Rates
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Point: Estimates may be unreliable and thus invalid
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No action should be taken until biodiversity loss is
demonstrated and shown to be harmful
Counterpoint: Wilson – Projections using areaspecies relationships in tropical settings (where most
of biodiversity loss currently is happening) are
conservative
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Tropical species have localized distributions that make
them especially vulnerable to habitat loss
Damaging loss of genetic diversity may occur, even if
outright extinction of a species doesn’t happen
Biodiversity – Definitions and Assessment
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D.
Biodiversity Hotspots
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Myers – Up to 20% of the world’s plant species and
more than 20% of the animal species are confined to
0.5% of the land surface
Biodiversity Hotspot – Area with high degree of
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Biodiversity
Endemism
Risk of habitat degradation/loss
Concept originally intended for tropical and
subtropical areas
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Endemism less prevalent in temperate and polar regions
Biodiversity – Factors
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A.
Nutrient Availability
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Oligotrophic
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Dominated by a few species able to survive on limited
nutrients
Low diversity, Low biomass
Mesotrophic
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Support greater numbers of species
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Rapid colonizers held in check by nutrient limitation
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Less aggressive species capable of surviving
High diversity, Medium biomass
Eutrophic
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Dominated by a few species able to grow and/or
colonize rapidly with abundant nutrients
Low diversity, High biomass
Biodiversity – Factors
II.
B.
Selective Colonization/Mortality
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Colonization
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2.
Excellent colonizers (r-selected) may dominate
newly available habitats
Mortality
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Predation
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Ex – Birds with colorful plumage
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Ex – Sea urchins (sushi)
Species-specific diseases/pests
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Ex – Dutch elm disease
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Ex – Western bark beetles
Biodiversity – Factors
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C.
Habitat Disturbance
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Non-selective habitat disturbance has
potential to increase diversity
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Prevents competitive exclusion
Intermediate disturbance  Maximum
diversity
Biodiversity – Factors
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C.
Habitat Disturbance
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Fire and fire-dependent species
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Ex – Peter’s Mountain Mallow (Iliamna corei)
Discovered in 1927 (50 plants)
Endemic to meadow in western Virginia
1986 - Three plants remaining
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Not setting seed
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Listed as endangered
Research on seeds indicated importance of fire
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Cracks hard seed coat, aiding germination
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Removes competing vegetation
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Had been suppressed in the area
Controlled burns in 1992 and 1993 led to
appearance of 500+ seedlings
Biodiversity – Factors
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D.
Habitat Fragmentation/Destruction
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Most significant factor causing species loss
Smaller habitats support fewer species and
smaller populations than large habitats
Population sizes tend to fluctuate more in
smaller habitats than large habitats
Reduced population  Lower genetic
diversity
Behavior of territorial species changes in
fragments, esp. when territory size ~
fragment size
Fragments may not support self-sustaining
populations (rely on immigration from
outside)
• Mount Hood
National Forest,
Oregon
• Patches due to
timber removal
Biodiversity – Factors
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D.
Habitat Fragmentation/Destruction
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Most significant factor causing species loss
Smaller habitats support fewer species and
smaller populations than large habitats
Population sizes tend to fluctuate more in
smaller habitats than large habitats
Reduced population  Lower genetic
diversity
Behavior of territorial species changes in
fragments, esp. when territory size ~
fragment size
Fragments may not support self-sustaining
populations (rely on immigration from
outside)
Biodiversity – Factors
II.
D.
Habitat Fragmentation/Destruction
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Fragmentation increases edge effects
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Positive effects
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Increased light to plant species at edges
Negative effects
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Increased predation by animals foraging at
habitat edge
Ex – Nesting success among migratory birds
in Midwestern forests lower in fragments
due to increased nest predation and
parasitism by cowbirds
Benefit – Herbivorous insects in fragmented
habitats experience less parasitism
(reduction of parasite’s habitat)
Biodiversity – Factors
II.
E.
Exotic Species
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Species invasions may profoundly affect
ecosystems
Detrimental exotic species usually are
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Superior competitors
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Ex – Argentine ants, starlings, zebra mussels
Effective predators
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Ex – Nile perch, mongeese