Download Apr 12 RK - University of San Diego

Biodiversity – Definitions and Assessment
I.
•
Major issue – Potential loss as a result of
human activities
Definitions
A.
•
Discussion requires clear consensus about what
biodiversity is and how it’s defined
Fundamental unit = species
What is a species??
Species
•
•
1.
•
•
Group of genetically similar organisms that interbreed
naturally and freely to produce viable, fertile offspring,
but do not share this behavior and outcome with
individuals of other species
Problem: Many people consider this definition to be
inadequate. Why??
Biodiversity – Definitions and Assessment
I.
A.
Definitions
1.
Species
a.
b.
c.
d.
Asexual Reproduction/Parthenogenesis
•
All prokaryotes
•
Some protists, fungi, plants, animals
Interbreeding Naturally & Freely
•
Some isolated populations could interbreed if
geographic barrier could be surmounted
•
Separate species? Subspecies? Populations?
Natural Hybrids
•
Ex – Horse + Donkey  Mule
•
Ex – Queen + Blue  Townsend’s Angelfish
•
Separate species? If a natural hybrid disappears, is
it really gone so long as parent species remain?
Polymorphism
•
Ex - Hamlets
•
How different must two species be to constitute
separate species? Humans and chimpanzees are
estimated to be 98% identical at the DNA level.
Biodiversity – Definitions and Assessment
I.
A.
Definitions
1.
Species
a.
b.
c.
d.
Asexual Reproduction/Parthenogenesis
•
All prokaryotes
•
Some protists, fungi, plants, animals
Interbreeding Naturally & Freely
•
Some isolated populations could interbreed if
geographic barrier could be surmounted
•
Separate species? Subspecies? Populations?
Natural Hybrids
•
Ex – Horse + Donkey  Mule
•
Ex – Queen + Blue  Townsend’s Angelfish
•
Separate species? If a natural hybrid disappears, is
it really gone so long as parent species remain?
Polymorphism
•
Ex - Hamlets
•
How different must two species be to constitute
separate species? Humans and chimpanzees are
estimated to be 98% identical at the DNA level.
Blue
Queen
Townsend’s
Biodiversity – Definitions and Assessment
I.
A.
Definitions
1.
Species
a.
b.
c.
d.
Asexual Reproduction/Parthenogenesis
•
All prokaryotes
•
Some protists, fungi, plants, animals
Geographic Isolation
•
Populations could interbreed if geographic barrier could
be surmounted
•
Separate species? Subspecies? Populations?
Natural Hybrids
•
Ex – Horse + Donkey  Mule
•
Ex – Queen + Blue  Townsend’s Angelfish
•
Separate species? If a natural hybrid disappears, is it
really gone so long as parent species remain?
•
Quagga
Polymorphism
•
Ex - Hamlets
•
How different must two species be to constitute separate
species? Humans and chimpanzees are estimated to be
98% identical at the DNA level.
Barred
Black
Golden
Blue
Indigo
Yellowtail
Biodiversity – Definitions and Assessment
I.
A.
Definitions
•
•
•
•
2.
How do we identify a species?
How do we quantify the number of species in an area
when there is disagreement about what constitutes a
species?
Recently: Focus on preservation of processes that lead
to speciation
What processes produce and maintain species?
Reproductive Isolation
•
•
•
Many factors can prevent individuals from interbreeding
Prezygotic
•
Act prior to fertilization
Postzygotic
•
Act following fertilization
Time of Day
Time of Year
Courtship
Sounds/Songs
Bullfrog x
Leopard Frog
Flowers
Fiddler Crabs
Horse (2n=64) x
Donkey (2n=62) 
Mule (2n=63)
Plants
Broadcast Spawners
Biodiversity – Definitions and Assessment
I.
A.
Definitions
3.
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
•
Often cited incorrectly as “biodiversity”
•
Fairly simple to estimate from rarefaction curves
2) Evenness – Proportions of species in a community
•
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
3.
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
•
Often cited incorrectly as “biodiversity”
•
Fairly simple to estimate from rarefaction curves
2) Evenness – Proportions of species in a community
•
More difficult to determine (requires more complete
survey)
Genetic Diversity – Variety of genotypes
Ecosystem Diversity – Variety of habitat types
Biodiversity – Definitions and Assessment
I.
B.
Estimates of Biodiversity
•
Described species ~ 1.8 million
•
•
•
•
•
Estimates range from 5 – 30 million
•
C.
Insects > 1,000,000 species
Plants > 290,000 species
Probably an underestimate
•
Only ~5000 species of bacteria
Less conspicuous species studied less often
Average estimate ~ 17.5 million
Estimates of Extinction Rates
•
•
Current estimates ~ 17,500 species year-1
•
1 out of every 1000 species on Earth each year
“Background” rate from fossil record
•
1 out of every 1-10 million species on Earth each
year
Biodiversity – Definitions and Assessment
I.
C.
Estimates of Extinction Rates
•
Problems
a.
b.
c.
Difficult to know when a species is extinct
•
Ex – Coelacanth, ivory billed woodpecker, giant
lemur
Extinctions may not happen immediately
•
Short-lived species show effects rapidly
•
Long-lived species may appear to be unaffected for
long periods of time
•
“Biologically extinct” – Populations not selfsustaining
•
“Living dead” - Janzen
Uncertainty about number of species in an area
•
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
•
Consideration: Wilson – Projections in tropical
settings (where most of biodiversity loss currently is
happening) are conservative
•
•
•
•
•
•
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 – Factors
II.
A.
Selective Mortality
•
Species-specific diseases/pests
•
•
•
Ex – Dutch elm disease
Ex – Western bark beetles
Predation
•
•
Ex – Birds with colorful plumage
Ex – Sea urchins (sushi)
Biodiversity – Factors
II.
B.
Habitat Disturbance
•
Non-selective habitat disturbance has
potential to increase diversity
•
•
Prevents competitive exclusion
Intermediate disturbance  Maximum
diversity
Biodiversity – Factors
II.
B.
Habitat Disturbance
•
Fire and fire-dependent species
•
•
•
•
•
•
Ex – Peter’s Mountain Mallow (Iliamna corei)
Discovered in 1927 (50 plants)
Endemic to meadow in western Virginia
1986 - Three plants remaining
•
Not setting seed
•
Listed as endangered
Research on seeds indicated importance of fire
•
Cracks hard seed coat, aiding germination
•
Removes competing vegetation
•
Had been suppressed in the area
Controlled burns in 1992 and 1993 led to
appearance of 500+ seedlings
Biodiversity – Factors
II.
C.
Habitat Fragmentation/Destruction
•
•
•
•
•
•
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.
C.
Habitat Fragmentation/Destruction
•
•
•
•
•
•
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.
C.
Habitat Fragmentation/Destruction
•
Fragmentation increases edge effects
•
•
•
•
Positive effects
•
Increased light to plant species at edges
Negative effects
•
Increased predation by animals foraging at
habitat edge
Ex – Nesting success among migratory birds
in Midwestern forests was 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 – Value
III.
A.
Value to Humans
•
Biodiversity loss could lead to removal of species that
benefit humans but aren’t cultivated currently
•
•
Ex – Chapin et al. suggested increase in frequency of Lyme
disease during 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
•
•
Counter – Many pharmaceutical companies now use directed
design to search for new drugs
Question – How do we know whether a species has value?
•
•
•
Problem – Benefits may not be obvious
Difficult to convince people that it’s important to preserve
something with no immediately apparent intrinsic value to them
Ex – Economic value of viral resistance added to commercial
strains of perennial corn through hybridization with teosinte
(Mexican wild grass) is ~ $230-300 million/year
III. Biodiversity – Value
B.
Ecosystem Value
•
1.
Biodiversity can have large effects on
ecosystem productivity and stability
Benefits of biodiversity
a.
Productivity
•
Halving species richness reduces productivity
by 10-20% (Tilman)
b. Nutrient retention
•
Loss of nutrients through leaching is reduced
when diversity is high
•
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.
•
•
Ecosystem stability
Mechanism
•
Multiple species within a trophic level compete for
resources
•
If the abundance of one species declines due to
perturbation, competing species may increase in
abundance
•
Individual species abundances may vary, but community
as a whole is more stable with more species
Consequences
•
High diversity doesn’t guarantee that individual
populations won’t fluctuate
•
Ex – Higher diversity (unfertilized) plots of native plant
species
1)
Maintained more biomass during drought than lower
diversity (fertilized) plots
2)
Conferred greater resistance to pests and diseases
3)
Showed reduced predation by herbivorous insects and
reduced invasion by weeds
Biodiversity – Value
III.
B.
Ecosystem Value
2.
Considerations
a.
•
b.
•
•
Species richness vs. Species evenness
Simple species richness may be deceptive as an indicator of
biodiversity and ecosystem stability
•
Evenness usually responds more rapidly to perturbation
than richness and may have important ecosystem
consequences
•
Richness is typical focus of studies and policy decisions
Importance of individual species
Different species affect ecosystems in different ways (keystone
species vs. non-keystone species)
•
Ex – Sea otters/Sea urchins/Kelp forests in eastern Pacific
Ocean
•
Ex – Pack ice/Krill/Salps in Southern Ocean
Question - How many species are required to maintain
“normal” ecosystem function and stability?
•
No magic number
•
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.
•
Strategies outlined in Convention on Biological
Diversity
•
•
•
•
•
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
•
•
Primary use of in situ conservation
Use of ex situ measures as a complement