Nematode trophic composition, as illustrated in Fig. 6, was based on Wieser’s four trophic group scheme. Although it is becoming accepted that Wieser’s classification may not accurately represent real feeding groups, which are more complex , it is still considered ecologically informative . In order to examine treatment effects on the trophic composition of other
nematode species, Diplolaimella sp., a non-selective deposit feeder (Type 1B), which occurred in extremely high numbers in the detritus-enriched samples, is not included in Fig. 7. A general trend was observed that the highest numbers of non-selective deposit feeders (Type 1B) shifted from controls (C) on day 1 to low dose samples (L) on day 10 then to medium dose samples (M) on day 30 and, finally, to high dose samples (H) on day 60 post-placement. Other groups showed a similar trend but with a time lag. For example, epi-growth feeders (Type 2A) had the highest numbers in the control from
days 1 to 10 post-placement. After 30 days, numbers in the control and medium dose samples were both high. The highest numbers occurred in the high dose samples 60 days post-placement. By the end of the experiment, all the feeding groups had obtained their highest absolute numbers in the high dose samples (Fig. 7). The relative abundance of the four trophic groups were, however, not very different from each other between the field control and different levels of treatment if the two numerically dominant species,namely Parastomanema sp. and Diplolaimella sp., were not included (Fig. 8A,B).