I. Biodiversity – Definitions and Assessment

A. Definitions2. 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. Definitions2. 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. Keystone Species

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• Around 300 new species described each day• Average estimate ~ 17.5 million

• Splitting of taxa more common than lumping• Tendency to increase number of described species• Cryptic species

I. Biodiversity – Definitions and Assessment

C. Estimates of Extinction Rates• Geological history

• Periods of extinction followed by periods of rapid speciation (every ~ 26 million years)

• How do we estimate rates of extinction??1. Problems

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

b. Species distributed unevenly (patchy distribution)• Species affected unevenly by habitat loss

c. 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

d. 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 Rates2. Estimation Methods

• Area-species relationship (MacArthur & Wilson)

a. Estimate biodiversity for a small area

b. Extrapolate estimate to area of habitat• Species ~ Area0.25 (0.15-0.35)• Increase area 10X Increase species 2X

c. Estimate rate at which ecosystem area is being reduced

d. Calculate extinction rate based on predicted reduction in species richness from reduction in habitat area

• Current estimate ~ 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 Rates2. Estimation Methods

• Area-species relationship (MacArthur & Wilson)a. Estimate biodiversity for a small areab. Extrapolate estimate to area of habitat

• Species ~ Area0.25 (0.15-0.35)• Increase area 10X Increase species 2X

c. Estimate rate at which ecosystem area is being reducedd. Calculate extinction rate based on predicted reduction

in species richness from reduction in habitat area• Current estimates ~ 17,500 species year-1

• 1 out of every 1000 species on Earth each year• Myers – 40,000 year-1

• Lomborg – 1033 documented from 1600 – 1998• The Skeptical Environmentalist

• “Background” rate from fossil record• 1 out of every 1-10 million species year-1

I. Biodiversity – Definitions and Assessment

C. Estimates of Extinction Rates• Point: Estimates may be unreliable and thus invalid

• No action should be taken until biodiversity loss is demonstrated and shown to be harmful

• Counterpoint: Wilson – Projections using area-species relationships 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

I. Biodiversity – Definitions and Assessment

D. Biodiversity Hotspots• 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• Biodiversity• Endemism • Risk of habitat degradation/loss

• Concept originally intended for tropical and subtropical areas

• Endemism less prevalent in temperate and polar regions

II. Biodiversity – Factors

A. Nutrient Availability1. Oligotrophic

• Dominated by a few species able to survive on limited nutrients

• Low diversity, Low biomass

2. Mesotrophic• Support greater numbers of species

• Rapid colonizers held in check by nutrient limitation• Less aggressive species capable of surviving

• High diversity, Medium biomass

3. Eutrophic• Dominated by a few species able to grow and/or

colonize rapidly with abundant nutrients• Low diversity, High biomass

II. Biodiversity – Factors

B. Selective Colonization/Mortality1. Colonization

• Excellent colonizers (r-selected) may dominate newly available habitats

2. Mortality• Predation

• Ex – Birds with colorful plumage• Ex – Sea urchins (sushi)

• Species-specific diseases/pests• Ex – Dutch elm disease• Ex – Western bark beetles

II. Biodiversity – Factors

C. Habitat Disturbance• Non-selective habitat disturbance has

potential to increase diversity• Prevents competitive exclusion

• Intermediate disturbance Maximum diversity

II. Biodiversity – Factors

C. 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

D. 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

D. 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

D. 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 lower in fragments due to increased nest predation and parasitism by cowbirds

II. Biodiversity – Factors

E. Exotic Species• Species invasions may profoundly affect

ecosystems• Detrimental exotic species usually are

• Superior competitors• Ex – Argentine ants, starlings, zebra mussels

• Effective predators• Ex – Nile perch, mongeese

II. Biodiversity – Factors

E. Exotic Species1. Zebra mussel

• Competitor in Great Lakes and elsewhere• Transported from Europe in ballast water• Fouling organism

• Restricts movement of water through intake pipes

• Colonizes boat hulls, pier pilings, buoys, etc.• Fouls other organisms (clams, mussels)

• Filter feeder – removes larvae and particulate material• Outcompetes native shellfish species for food

and space• Removes larvae from water

II. Biodiversity – Factors

E. Exotic Species2. Mongoose

• Predator in Hawaii• Introduced in 1883 to combat rat population• Prey on native birds

3. Lionfish• 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 Brown tree snake - Guam

Argentine ants - California Caulerpa taxifolia - California

III. Biodiversity – Value

A. Value to Humans• Economic

• 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

• 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

• Counter – Many pharmaceutical companies now use directed design to search for new drugs

III. Biodiversity – Value

A. Value to Humans

• 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 (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

III. Biodiversity – Value

B. Ecosystem Value• Biodiversity can have large effects on ecosystem

stability and productivity1. Benefits of biodiversity

a. Productivity• Halving species richness reduces productivity by

10-20% (Tilman)• Average plot with one plant species is less than half

as productive as a plot with 24-32 species• Question – Can these results be extrapolated to

other systems and time/space scales?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 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 maintained more biomass during drought than lower diversity (fertilized) plots

• High diversity may confer greater resistance to pests and diseases

• Ex – Higher diversity plots of native plant species had greater resistance to fungal diseases, 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• Charismatic megafauna: What about non-charismatic 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• 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