Soil food webs in agricultural ecosystems - Microbial Ecology in Sustainable Agroecosystems - page 73

Table 4.4 Estimates of the Proportion of Energy (Indexed by Carbon) That the Different
Functional Groups Potentially Derive from within the Bacterial, Fungal, or Plant Roots Energy
Channels within the Soil Food Web of the CPER

Energy channel

Functional group Bacteria Fungi Root

Protozoa

Flagellates 100 0 0

Amoebae 100 0 0

Ciliates 100 0 0

Nematodes

Phytophagous nematodes 0 0 100

Mycophagous nematodes 0 90 10

Omnivores nematodes 100 0 0

Bacteriophagous nematodes 100 0 0

Predatory nematodes 68.67 3.50 27.83

Microarthropods

Collembola 0 90 10

Cryptostigmata 0 90 10

Mycophagous Prostigmata 0 90 10

Nematophagous mites 66.70 3.78 29.52

Predatory mites 39.54 38.56 21.91

Source: From Moore, J.C., D.E. Walter, and H.W. Hunt. 1988. Arthropod regulation of micro- and mesobiota in
below-ground detrital food webs. Annual Review of Entomology 33:419-439.

4.4 Patterns and stability
Are the observed patterns in biomasses, energy fluxes, and interaction strengths related
in any way to the stability of the systems? Odum's assessment of ecosystem development
alluded to the connections between the energetic organization of the ecosystem and sta-
bility. The distribution of biomass and the magnitude of flows within the energy flow
description constitute the energetic organization of the system. de Ruiter et al. (1995)
assessed whether these patterns within the energetic organization of the system are
linked to asymptotic stability using the eigenvalue-based analysis of the Jacobian matrix
described. Two approaches were taken. In the first approach, pairs of elements within the
Jacobian matrix associated with individual trophic interactions were disturbed by varying
the values within plus or minus two times their mean to determine the sensitivity of the
interaction to change and its impact on the stability of the web as a whole. The sensitiv-
ity of interactions and their impact on stability did not correlate to the magnitude of their
fluxes ( Figure 4.5 ) . In the second approach, the connectedness structure and positioning
of the nonzero elements of the Jacobian matrix were preserved, but each of the paired ele-
ments within the matrix was transposed with other pairs. The webs that possessed the
observed patterning of interaction strengths that emerged from the field data were more
stable than those that possessed the manipulated arrangements ( Figure 4.6 ) .
The observed compartmentalized organization of the food webs into interacting
energy channels is consistent with the patterns expected for systems that are hierarchi-
cally organized as a collection of interacting subsystems. May (1972) had proposed that