Species diversity- Global decline, local rise

lou jost loujost@yahoo.com
Wed, 11 Aug 2010 11:10:12 PDT
Thanks for posting this. However, it is bad science, and should not give us rare plant lovers any reason to be happy. The paper assumes that species diversity is best measured by just counting the number of species present ("species richness"). This is an ecologically meaningless measure. An ecologically meaningful measure of diversity takes species relative abundances into account. Such measures include the exponential of Shannon entropy and the inverse Simpson concentration. For a given number of species, a more even distribution of abundances will have a higher diversity according to these measures. These paint a completely different picture of what has happened on islands or other habitats after the introduction of invasive alien species. Yes, the total count of species goes up, because the native species are not quite extinct. But according to these more meaningful measures of diversity, the diversity is usually lower after the introduction of
 aliens, because a small number of alien species dominate the landscape. The remnant native plants become rare or local and they  play a numerically minor role in the interactions among organisms in those ecosystems. 


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