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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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 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