Biodiversity

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Biodiversity

• The number, variety and variability of organisms
• Or, number of spp. in a defined area
• Larger the number, the greater the biodiversity
• Also called species richness

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Comparing Biodiversity

• Areas being compared should be similar in size
• Species richness tends to increase w/ increasing
  area
• Link between area size and species richness
  called species-area relationship
• Species-area relationship tends to be non-linear
• Species-area curve
• Curve changes w/ species richness

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Species Evenness

• Species richness doesnt tell enough about
  biodiversity
• What about rarity and distribution?
• Species evenness reveals if species in sample
  area occur in roughly similar amounts
• E.g.
• 3 spp. Of 10-10-10 in area even distribution
• 3 spp. Of 25-3-2 in area uneven distribution
• Species evenness is
• Difficult and expensive
• No theory on what evenness should be

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How Many Species on Earth?

• Science recognizes prox. 1.7 million
• From viruses to Giant Sequoia Blue Whale
• Prox. 64 are arthropods!
• lt3 are vertebrates
• Total unknown but estimated at 4-10 million
• Most unknowns are small
• Thousands identified annually

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Genetic Biodiversity

• Biodiversity not limited to species
• A species may contain many genotypes
• Can be geographic patterns of genetic variability
• May affect form, behavior, functions, etc.
• Study to reveal relationships between
• genetic diversity
• Geography
• Environment
• People

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Diversity Gradients

• Diversity tends to vary by latitude
• Species diversity lowest near poles highest
  near equator
• Except peninsulas and islands
• Usually have less diversity than nearby mainland
• Species richness also increases as approach
  equator
• True for marine aquatic environments too
• Tropical rainforests are most biodiverse regions
• Diversity tends to vary by altitude
• Decreases w/ increasing altitude

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a tree diversity b mammal diversity c bird
diversity
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Data for Himalayan Mountains
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Now, well turn to the controls on organisms