Re: Species diversity

From: Elaine Ingham (Soilfoodweb@AOL.COM)
Date: Tue Nov 05 2002 - 14:14:14 EST


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.

Elaine Ingham
President, Soil Foodweb Inc.
www.soilfoodweb.com


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