Biodiversity

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					Biodiversity

What is biodiversity?
• “Biological diversity is the wealth of life on earth, the millions of plants,
  animals, and microorganisms, the genes they contain, and the intricate
  ecosystems they help to build into the living environment.” (WWF 1989)

Levels of biodiversity
• Genetic diversity: differences in genes
• Species diversity: differences within and between populations, AND between
  different species, taxa diversity
• Ecosystem diversity: different habitats, biological communities, and ecosystem
  processes

Abundance and diversity
• Abundance is the total number of organisms in a community
• Diversity is the number of different species, ecological niches, or genetic
  variation
   – Abundance of a particular species often inversely related to community
     diversity
   – As general rule, diversity decreases and abundance within species
     increases when moving from the equator to the poles

How many species are there?
• Estimates range from 10 - 50 million species, of which only 1.4 million have
  been described.
   – A collection from the canopy of only 19 rainforest trees in Panama yielded
     950 species of beetles, of which less than 20% had been previously
     described

Species diversity
• Richness = # of species in a given area/community
Species diversity
• Evenness = equity of numbers of individuals of each species in a given area
   – Shannon Index
• More difficult to measure in practice
   – Some use diversity and richness interchangeably

Does biodiversity affect ecosystem properties?

Biodiversity increased stability
• Plots with more species showed less year-to-year variation in biomass

Biodiversity increased stability
• During a drought, the decline in biomass was negatively related to species
  richness

Biodiversity increased resistance to invasion

Biodiversity increased productivity

More to come….
• Tilman’s work still being evaluated
• Active area of research
Patterns in biodiversity
• Latitude
• Altitude
• Spatial heterogeneity
• Productivity
• Climate stability and predictability
• Predation
• Competition
• Area
Diversity decreases with latitude
• Species diversity cline

Latitudinal variation
• Species richness is higher in tropical than temperate regions
   – Forest birds of Central and South America

Altitudinal variation
• Richness often declines with increasing altitude
    – New Guinea birds

Habitat complexity
• Richness increases with structural complexity of the habitat
   – Southern U.S. lizards
• More complex or variable habitats provide more ‘niches’ for species to occupy

Productivity
• Effect of productivity varies with scale
   – Local scale
   – Regional scale

Productivity at the local scale
Productivity at the regional scale

Climate
• More stable climates have greater richness

Predation
• In diverse communities, predators reduce the abundance of competitively
  superior species allowing more species to coexist and allowing more niche
  overlap between competitors
   – Pisaster

Competition
• Higher productivity = larger population sizes
• Larger populations = more interspecific competition
• More competition = more specialization
• More specialization = more species packed into a community
Why is diversity highest in the tropics?
• Competing hypotheses
   – Evolutionary age of tropics
   – Increased productivity
   – Stable climate
   – Intense predation reduces competition
   – Spatial heterogeneity

Area
• In general, the larger the area, the larger the number of species
   – sampling effects
   – number of different habitats increases



Size and diversity
• More birds on larger islands
Island biogeography
• Model that explains species richness on islands based on
    – Size of island
    – Distance of island from mainland

Island biogeography
• The equilibrium number of species S on an island reflects a balance between
   colonization and extinction
• “Equilibrium” applies only to species richness, not species composition
Island biogeography
• Colonization rate decreases with species richness
• colonization rate (C) determined by isolation of island
    – Further islands have lower colonization rates

Island biogeography
• Extinction rate increases with species richness
• Extinction rate (E) determined by size of island
    – Smaller islands lead to smaller populations, which have a greater chance of
      extinction

Island biogeography
• Equilibrium richness is where colonization rate equals extinction rate


IBT predictions

Breeding birds species richness on isolated woodlots in Illinois

				
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