ENVIRONMENTAL SCIENCE : ECOSYSTEM 123
DECOMPOSERS WITH VARYING RELATIONS
Some decomposer organism’s cannot be assigned a rigid or fixed position in the food
web. Their trophic relations can vary from time to time.
- Nectroph: Some decomposers are nectrophs. They cause rapid death of the food
source because they have a short-term exploitation of living organism. Nectrophs
include may plant parasitic microbes as well as some herbivores, predators, and
microtrophs (organisms which feed on living bacteria and fungi.) - Biotrophs: On the other hand biotopes resort to a long-term exploitation of their
living food resource. For example, root-feeding nematodes and aphids, obligate
plant parasites, e.g., and mycorhizae and root nodules, etc. - Saprotophs: The apostrophes utilize food already dead, and most of the decomposers
belong to this category.
Decomposers occupying different trophic levels
There are some such organisms causing decompositions as can occupy various trophic
levels under different conditions. For instance the root parasites like Fusarium and
Thizoctonia are necrotrophs, which often show a saprotrophic tendency. In the same way,
the predators (foxes and kites) sometime behave as saprotrophs. Biotrophs sometime act as
necrotrophs or as saprotrophs.
Soul Invertebrates And Termites
There are some soil invertebrates e.g. earthworms and collembolans distribute organic
matter throughout the soil whereas others e.g. termites and ants, concentrate it at localized
sites around or near the royal chamber or in mounds. The following table shows the estimated
activities of major groups of soil animals.
Table 3.2 : Soil Animals’ ActivitesGroup (m-2) Density R/Q Production Excretory C/N ratio
Respiratory efficiency products
quotientProtozoa 0.1-x1000 0.31-0.71 0.34-0.40 Urea ammonia 5
Nematodes 3.9-0-6x106 04.41-0.96 0.04-0.13 Urea ammonia 7.5-12
aminoacids
Annelids 0.650 <0.07 Urea
(eartworms)
Molluscs 0-8500 0.82 Ammonia. urea,
Amino acids
Arthropods
Collembola 700-40,00
Ants, termiter 1000-10,000 Uric acid urates