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6 - Community group of species living together Biodiversity...

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Community – group of species living together Biodiversity – the number and types of species in a community 1. How species originate? - Charles Darwin: evolution by natural selection 2. How many species are there? - How do we measure the number of species in a community? - What determines the number of species in a community? - What is the relationship between the diversity and stability of a community? Problems: Description & measurement of communities - difficult to produce complete list of species in a community due to: 1. taxonomic problems - definition for species 2. disproportionate attention on vertebrates & neglect of other taxa - vertebrates ~ 3% of all species - received disproportionate attention - other groups often neglected - number of currently classified species ~ 1.7 million - plant, algae + fungi ~ 450,000 (fungi probably > 1,000,000) - insects ~ 750,000 (many still unknown, probably >> 1,000,000) - vertebrates ~ 50,000
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3. geographical bias - 1 million species known from temperate regions - assuming ratio of tropic : temperate = 2 : 1 (more species in the tropics) - total ~ 3 million species - assuming 50% of all species still unknown, total = 6 million species - true ratio of tropic : temperate probably >> 2 4. species diversity in rainforests unknown - estimate of insect species in rainforest by Terry Erwin eg. Beetles on Luehea seemannii tree in Panama - release quick-effect insecticide over 19 trees - collect all insects below - total number of beetle species = 1,100 - assuming ~ 15% are host specific to L. seemannii ~ 160 species - beetles comprise ~ 40% of all arthropods - total arthropods specific to L. seemannii ~ 400 - assuming ratio of canopy to roots = 2 : 1 - total arthropods = 400 (canopy) + 200 (roots) = 600 - total number of tree species in tropical rain forest ~ 50,000 - total number of arthropods species ~ 30 million (50,000 x 600) - total number of species (~ 30% are arthropod) ~ 100 million
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Uncertainties in Terry Erwin’study i) what percentage of beetles are really host specific? ii) do beetles make up 40% of all arthropods? iii) do arthropods really make up 30% of all species? iv) is ratio of canopy to root really 2:1? Conclusions i) tropical rainforests contain huge amount of biodiversity ii) true level of biodiversity in tropical rainforests is unknown
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