Soil food webs in agricultural ecosystems - Microbial Ecology in Sustainable Agroecosystems - page 76

Figure 4.7 The dominant eigenvalues for models of two parallel food chains drawing energy from a
basal resource (e.g., detritus) and linked by a common predator along a gradient of resource alloca-
tion. The food chains differ in the rates that transfer and turnover consumed matter and energy, that
is, a fast bacterial energy channel and a slow fungal energy channel. The x -axis represents the pro-
portion of the basal resource that is consumed by the first consumer in the fast channel (p). The y -axis
represents the dominant eigenvalue (λ) for the system at each iteration of partitioning of resource.
The total amount of energy passing through each system is the same for each iteration, but the attack
ratio of the consumer of the fast channel differs. The dashed vertical lines represent unstable transi-
tions. Note that the most stable configuration occurs when the two channels are coupled and unsta-
ble (λ > 0) if most of the energy passes through either the fast channel or slow channel.
The analysis also revealed that the magnitude of individual interactions does not nec-
essarily equate to their importance to stability (Paine, 1980). Weak interactions, in terms of
both energy flow and per-capita effects, can have profound effects on stability (McCann et
al., 1998; de Ruiter et al., 1998). The analyses did indicate that the patterning of the interac-
tions and their relationships among one another appear to be more important than the
magnitude of the interactions per se (de Ruiter et al., 1995; Neutel et al., 2002). Observed
patterning of fluxes and interaction strengths possess a compartmentalized organizational
structure around energy channels (Moore et al., 1988, 2004; Rooney et al., 2006). On the
whole, the energetic organization of the food web defined in terms of the distribution
of biomass and fluxes and the arrangement of trophic interactions in the form of trophic
loops (sensu Neutel et al., 2002) is important to the stability and persistence of the system.