I. I.Biodiversity – Definitions and Assessment Major issue – Potential loss as a result of human activities A. A.Definitions Discussion requires clear.

I. Biodiversity – Definitions and Assessment

• Major issue – Potential loss as a result of human activities

A. Definitions• Discussion requires clear consensus about what

biodiversity is and how it’s defined• Fundamental unit = species• What is a species??

1. Species• 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??

I. Biodiversity – Definitions and Assessment

A. Definitions1. Species

a. Asexual Reproduction/Parthenogenesis• All prokaryotes• Some protists, fungi, plants, animals

b. Interbreeding Naturally & Freely• Some isolated populations could interbreed if

geographic barrier could be surmounted• Separate species? Subspecies? Populations?

c. 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?d. 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.

I. Biodiversity – Definitions and Assessment

A. Definitions1. Species

a. Asexual Reproduction/Parthenogenesis• All prokaryotes• Some protists, fungi, plants, animals

b. Interbreeding Naturally & Freely• Some isolated populations could interbreed if

geographic barrier could be surmounted• Separate species? Subspecies? Populations?

c. 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?d. 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

I. Biodiversity – Definitions and Assessment

A. Definitions1. Species

a. Asexual Reproduction/Parthenogenesis• All prokaryotes• Some protists, fungi, plants, animals

b. Geographic Isolation• Populations could interbreed if geographic barrier could

be surmounted• Separate species? Subspecies? Populations?

c. 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

d. 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

Blue

Golden

Indigo

Yellowtail

I. Biodiversity – Definitions and Assessment

A. Definitions• 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?

2. 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

Flowers

Fiddler Crabs

Plants

Broadcast Spawners

Bullfrog x

Leopard Frog

Horse (2n=64) x

Donkey (2n=62) Mule (2n=63)

I. Biodiversity – Definitions and Assessment

A. Definitions3. Components of Biodiversity

• The term “biodiversity” often is used incorrectly or incompletely

• Not synonymous with “species diversity”• Encompasses three measures

a. 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)

b. Genetic Diversity – Variety of genotypes

c. Ecosystem Diversity – Variety of habitat types

I. Biodiversity – Definitions and Assessment

A. Definitions3. Components of Biodiversity

• The term “biodiversity” often is used incorrectly or incompletely

• Not synonymous with “species diversity”• Encompasses three measures

a. 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)

b. Genetic Diversity – Variety of genotypes

c. Ecosystem Diversity – Variety of habitat types

I. Biodiversity – Definitions and Assessment

B. Estimates of Biodiversity• Described species ~ 1.8 million

• Insects > 1,000,000 species• Plants > 290,000 species• Probably an underestimate

• Only ~5000 species of bacteria• Less conspicuous species studied less often

• Estimates range from 5 – 30 million• Average estimate ~ 17.5 million

C. 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

I. Biodiversity – Definitions and Assessment

C. Estimates of Extinction Rates• Problems

a. Difficult to know when a species is extinct• Ex – Coelacanth, ivory billed woodpecker, giant

lemurb. 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 self-

sustaining• “Living dead” - Janzen

c. 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”

I. Biodiversity – Definitions and Assessment

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

• • • •

II. Biodiversity – Factors

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)

II. Biodiversity – Factors

B. Habitat Disturbance• Non-selective habitat disturbance has

potential to increase diversity• Prevents competitive exclusion

• Intermediate disturbance Maximum diversity

II. Biodiversity – Factors

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

II. Biodiversity – Factors

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

II. Biodiversity – Factors

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)

II. Biodiversity – Factors

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)

III. Biodiversity – Value

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• Biodiversity can have large effects on

ecosystem productivity and stability

1. Benefits of biodiversitya. 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?

III. Biodiversity – Value

B. Ecosystem Value1. 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) plots2) Conferred greater resistance to pests and diseases3) Showed reduced predation by herbivorous insects and

reduced invasion by weeds

III. Biodiversity – Value

B. Ecosystem Value2. Considerations

a. 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 decisionsb. 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

IV. Biodiversity – Management

• 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