Dear Veronica

In these areas we always encounter problems of definition. Certainly, nematodes can be separated into feeding (tropic) groups - herbivores, bacterivores, fungivores, and others. But within each of these groups there is enormous biological diversity: differences in life-cycle length, longevity, fecundity, metabolic rates, etc., so we do not have a very clear understanding of the "function" of nematodes in the soil ecosystem simply by calling them herbivores. For example, herbivores have the "function" of introducing carbon and energy into the soil food web by withdrawing resources directly from plant roots. But some grow and reproduce rapidly, others more slowly; some feed on root hairs, others on specialized transfer cells. So the "function" occurs at different rates. Now, if we group the herbivores into smaller units, for example migratory root-hair feeders with similar biological characteristics, we can be more precise about the rate at which the function is performed in each such unit.

So, I consider a functional guild to be a group of organisms that have similar growth, reproductive and metabolic characteristics and perform the same ecological function. We feel that, in most cases, such similarities are adequately described by categorizing nematodes with similar feeding habits at the family level (e.g., Bongers and Bongers, 1998, and in Bongers and Ferris, 2000).

Similarly, the argument can be developed for bacterivores. Rhabditids have different metabolic rates and life cycles than cephalobids. Both feed on bacteria, but the rate at which the ecological function of nitrogen mineralization occurs is very different.

Of course, the level of resolution must be decided based on what is practical. In fact we could consider each individual species to be sufficiently different that they should be considered as separate functional groups, but that does not allow us to achieve the simplification that we seek in studying ecosystem function.

Hope this helps.

Howard Ferris

At 0855 AM 10/23/2001 -0300, you wrote

Dear Howard Ferris,
I´m from Uruguay and I study free-living nematodes.
I´m writing a project and I have no clear if I could be considered
nematodes as functional groups. I have read many papers about
classification of nematodes in trophic groups but I have not enough
arguments to this.
I have been discussed about concepts (functional groups, guilds,
assemblages) with my colleage but they don´t work with soil organisms so
that they have different ideas according their study object.
Could you help me about my doubt? I contact with you because I have
read your publications and you have experience in Nematology.
Thank you very much
Verónica Korenko
Section Ecology
Science Faculty