[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: Species diversity
If there are no individuals of a species, or if there are no species present, the number involved is zero. You can't have a negative number of species, or a negative number of individuals. A "species richness" or a "species diversity" index that assigns a negative number to species that is present is mis-leading and inappropriate. At the very least, an explanation of why a negative value would be assigned is required.
There is no species diversity or species richness index found in any introductory text book - certainly not Shannon-Weiner or Simpsons - that calculate a negative species richness or species diversity for any part of the community of any set of organisms.
No one in ecology makes the mistake of calling something Species Richness Diversity. Species richness is simply the number of species per unit area or volume. Species diversity requires knowledge about the number of individuals of each species per unit area or volume. Species diversity requires a knowledge of species richness. The calculations in text books are either for species richness or for species diversity. Do not mix the two up.
To quote researchers at Cornell University, the plate count approach is "worthless" for assessment of species diversity in environmental samples. Joel Gruver from North Carolina State University has had his say about the usefulness of plate counts in assessing species diversity in soil or compost samples on this list serve already. Plate counts as an approach to assessing species diversity in environmental samples are not worth the money you pay for them.
Can plate count information be useful? That's a different question. Plate counts can be used to assess the number of individuals (colony forming units), or a "most probable number" of individuals, of certain species, if you KNOW that the species you want to know about grow in a certain specific set of conditions that you can reproduce in the laboratory.
Most bacteria or fungi in soil or compost do not grow on any plate medium. Estimates are that less than 0.1% of the known species of bacteria can grow on any plate medium. Even if you run six different media, you can't begin to get a reasonable assessment of species diversity using plate count approaches.
There has been some serious mis-information about the number of species of bacteria and fungi in compost, for example, because people do not understand that plate counts assess less than 0.1% of the set of species present in the compost. People tell me often that compost doesn't have many species of bacteria or fungi, based on plate count information.
Can we all, from this point on, please, exit this mis-information from our understanding? Compost has a huge number of bacterial and fungal species in it, based on the diversity of starting materials put into the compost, based on the number of unique DNA sequences that occur in compost, or soil or compost tea. Using molecular techniques, we can assess diversity.
Plate counts are NOT APPROPRIATE for assessing numbers of species of bacteria or fungi in any soil, compost or compost tea. Plate counts can be useful for assessing numbers of individuals a few species that we know the conditions for their growth, but that's about it.
President, Soil Foodweb Inc.