Transcript Biodiversity – Definitions and Assessment I. A. Definitions 2. Components of Biodiversity • a. b. c. The term “biodiversity” often is used incorrectly or incompletely • Not synonymous with “species diversity” • Encompasses three measures Species.

Biodiversity – Definitions and Assessment
I.
A.
Definitions
2.
Components of Biodiversity
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a.
b.
c.
The term “biodiversity” often is used incorrectly or
incompletely
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Not synonymous with “species diversity”
•
Encompasses three measures
Species Diversity
1) Species richness – Total number of species
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Often cited incorrectly as “biodiversity”
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Fairly simple to estimate from rarefaction curves
2) Evenness – Proportions of species in a community
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More difficult to determine (requires more complete
survey)
Genetic Diversity – Variety of genotypes
Ecosystem Diversity – Variety of habitat types
Biodiversity – Definitions and Assessment
I.
A.
Definitions
2.
Components of Biodiversity
•
a.
b.
c.
The term “biodiversity” often is used incorrectly or
incompletely
•
Not synonymous with “species diversity”
•
Encompasses three measures
Species Diversity
1) Species richness – Total number of species
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Often cited incorrectly as “biodiversity”
•
Fairly simple to estimate from rarefaction curves
2) Evenness – Proportions of species in a community
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More difficult to determine (requires more complete
survey)
Genetic Diversity – Variety of genotypes
Keystone Species
Biodiversity – Definitions and Assessment
I.
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
I.
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
a.
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
I.
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
II.
A.
Nutrient Availability
1.
Oligotrophic
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2.
Dominated by a few species able to survive on limited
nutrients
Low diversity, Low biomass
Mesotrophic
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3.
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
1.
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
II.
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
II.
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
II.
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
II.
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
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
Biodiversity – Factors
II.
E.
Exotic Species
1.
Zebra mussel
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Competitor in Great Lakes and elsewhere
Transported from Europe in ballast water
Fouling organism
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Restricts movement of water through intake
pipes
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Colonizes boat hulls, pier pilings, buoys, etc.
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Fouls other organisms (clams, mussels)
Filter feeder – removes larvae and particulate
material
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Outcompetes native shellfish species for food
and space
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Removes larvae from water
Biodiversity – Factors
II.
E.
Exotic Species
2.
Mongoose
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3.
Predator in Hawaii
Introduced in 1883 to combat rat population
Prey on native birds
Lionfish
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Venomous predator
Introduced in Caribbean/W Atlantic ca. early/mid
1990’s
Preys on 65+ spp. of fishes
No natural predators
Nile perch – Lake Victoria
Argentine ants - California
Brown tree snake - Guam
Caulerpa taxifolia - California
Biodiversity – Value
III.
A.
Value to Humans
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Economic
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Ex – Lomborg: $3-33 trillion annually
Biodiversity loss could lead to removal of species
that benefit humans but aren’t currently known to do
so
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Ex – Chapin et al. suggest increased frequency of Lyme
disease in 20th century may have been related to
increase in abundance of tick-bearing mice (once
controlled by food competition with passenger pigeons)
Species extinction reduces potential pool of species
containing chemical compounds with pharmaceutical
or industrial applications
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Counter – Many pharmaceutical companies now use
directed design to search for new drugs
Biodiversity – Value
III.
A.
Value to Humans
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Problem – Benefits may not be obvious
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Difficult to convince people that it’s important to
preserve something with no immediately apparent
intrinsic value to them (charisma?)
Ex – Economic value of viral resistance added to
commercial strains of perennial corn through
hybridization with teosinte (Mexican wild grass) is ~
$230-300 million
Ex – Weedy tomatoes from Peru
Discovered in 1962 during search for potatoes
Seeds sent to researcher at UC Davis who used plants
to breed with other tomatoes
In 1980 after nearly 10 generations of crossing and
backcrossing, new strains were produced with larger
fruit, improved pigmentation and increased
concentrations of sugars and soluble solids
Biodiversity – Value
III.
B.
Ecosystem Value
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1.
Biodiversity can have large effects on ecosystem
stability and productivity
Benefits of biodiversity
a.
b.
Productivity
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Halving species richness reduces productivity by
10-20% (Tilman)
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Average plot with one plant species is less than half
as productive as a plot with 24-32 species
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Question – Can these results be extrapolated to
other systems and time/space scales?
Nutrient retention
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Loss of nutrients through leaching is reduced when
diversity is high
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Caveat – Studies to date have focused on low
diversity communities (Why?); can those results be
generalized?
Biodiversity – Value
III.
B.
Ecosystem Value
1.
Benefits of biodiversity
c.
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Ecosystem stability
Mechanism
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Multiple species within a trophic level compete for
resources
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If abundance of one species declines due to perturbation,
competing species may increase in abundance
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Individual species abundances may vary, but community
as a whole is more stable with more species
Consequences
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High diversity doesn’t guarantee that individual
populations won’t fluctuate
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Ex – Higher diversity (unfertilized) plots of native plant
species maintained more biomass during drought than
lower diversity (fertilized) plots
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High diversity may confer greater resistance to pests and
diseases
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Ex – Higher diversity plots of native plant species had
greater resistance to fungal diseases, reduced predation
by herbivorous insects and reduced invasion by weeds
Biodiversity – Value
III.
B.
Ecosystem Value
2.
Considerations
a.
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b.
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Species richness vs. Species evenness
Simple species richness may be deceptive as an indicator of
biodiversity and ecosystem stability
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Evenness usually responds more rapidly to perturbation
than richness and may have important ecosystem
consequences
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Richness is typical focus of studies and policy decisions
Importance of individual species
Charismatic megafauna: What about non-charismatic species?
Different species affect ecosystems in different ways (keystone
species vs. non-keystone species)
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Ex – Sea otters/Sea urchins/Kelp forests in eastern Pacific
Ocean
Question: How many species are required to maintain “normal”
ecosystem function and stability?
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No magic number
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Losing one ant species in a tropical forest may have less
immediate impact than losing one species of fungus that
is crucial to nutrient cycling in the soil
Biodiversity – Management
IV.
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Strategies outlined in Convention on Biological
Diversity
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Developed between 1988 and 1992
Opened for ratification at UN Conference on
Environment and Development (Rio “Earth Summit”)
Ratified by 168 nations; went into force in Dec 1992
Objectives – “…the conservation of biological
diversity, the sustainable use of its components and
the fair and equitable sharing of the benefits arising
out of the utilization of genetic resources…”
Articles 8-9 specify a combination of in situ
and ex situ conservation measures
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Primary use of in situ conservation
Use of ex situ measures as a complement