Biodiversity

1

• Biodiversity Definitions and Assessment
• Estimates of Biodiversity
• Described species 1.8 million
• Insects gt 1,000,000 species
• Plants gt 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

2

• Biodiversity Definitions and Assessment
• 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??
• Problems
• Difficult to know when a species is extinct
• Ex Coelacanth, ivory billed woodpecker, giant
  lemur
• Species distributed unevenly (patchy
  distribution)
• Species affected unevenly by habitat loss
• 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
• 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

3

• Biodiversity Definitions and Assessment
• Estimates of Extinction Rates
• Estimation Methods
• Area-species relationship (MacArthur Wilson)
• Estimate biodiversity for a small area
• Extrapolate estimate to area of habitat
• Species Area0.25 (0.15-0.35)
• 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
• 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

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• Biodiversity Definitions and Assessment
• Estimates of Extinction Rates
• Estimation Methods
• Area-species relationship (MacArthur Wilson)
• Estimate biodiversity for a small area
• Extrapolate estimate to area of habitat
• Species Area0.25 (0.15-0.35)
• 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
• 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

6

• Biodiversity Definitions and Assessment
• 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 doesnt
  happen

7

• Biodiversity Definitions and Assessment
• Biodiversity Hotspots
• Myers Up to 20 of the worlds 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

8

• Biodiversity Factors
• Nutrient Availability
• Oligotrophic
• Dominated by a few species able to survive on
  limited nutrients
• Low diversity, Low biomass
• Mesotrophic
• Support greater numbers of species
• Rapid colonizers held in check by nutrient
  limitation
• Less aggressive species capable of surviving
• High diversity, Medium biomass
• Eutrophic
• Dominated by a few species able to grow and/or
  colonize rapidly with abundant nutrients
• Low diversity, High biomass

9

• Biodiversity Factors
• Selective Colonization/Mortality
• Colonization
• Excellent colonizers (r-selected) may dominate
  newly available habitats
• Mortality
• Predation
• Ex Birds with colorful plumage
• Ex Sea urchins (sushi)
• Species-specific diseases/pests
• Ex Dutch elm disease
• Ex Western bark beetles

10

• Biodiversity Factors
• Habitat Disturbance
• Non-selective habitat disturbance has potential
  to increase diversity
• Prevents competitive exclusion
• Intermediate disturbance ? Maximum diversity

11

• Biodiversity Factors
• Habitat Disturbance
• Fire and fire-dependent species
• Ex Peters 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

12

• Biodiversity Factors
• 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)

13

• Mount Hood National Forest, Oregon
• Patches due to timber removal

14

• Biodiversity Factors
• 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)

15

• Biodiversity Factors
• 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
  parasites habitat)

16

• Biodiversity Factors
• 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