Transcript Pages 304-308

Some groups contain more species than
others
• Species are not evenly
distributed among taxonomic
groups
- Insects predominate over all
other life-forms
- 40% of all insects are
beetles
• Groups accumulate species by
- Adaptive radiation
- Allopatric speciation
- Low rates of extinction
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Insects outnumber all other species
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Measuring biodiversity is not easy
• Out of the estimated 3 - 100 million species on Earth,
only 1.7 - 2 million species have been successfully
catalogued
• Very difficult to identify species
- Many remote spots on Earth remain unexplored
- Small organisms are easily overlooked
- Many species look identical until thoroughly examined
• Entomologist Terry Erwin found 163 beetle species
specialized on one tree species
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Species Richness
• Based solely on the number of species found in a given
area
- species richness (# species within the community)
R=s
where
s = the number of species
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Shannon-Weiner Diversity Index
• Combines two quantifiable measures:
- species richness (# species within the community)
- species equitability (how even are the numbers of individual
species)
• Calculated using the equation
H = - Pi(lnPi)
where Pi is the proportion of each species in the sample
and is equal to
ni/N
where
ni = the number of individuals in a given species i
N = the total number of individuals collected
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings