I. I.Biodiversity – Definitions and Assessment B. B.Estimates of Biodiversity Described species ~ 1.8 million Insects > 1,000,000 species Plants > 290,000.

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

• Benefit – Herbivorous insects in fragmented habitats experience less parasitism (reduction of parasite’s habitat)

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