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(a)
Real
100
50
0
1 0.1 0.01 1 0.1 0.01 1 0.1 0.01 1 0.1 0.01 1 0.1 0.01 1 0.1 0.01 1 0.1 0.01
(b)
Randomized
100
50
0
1 0.1 0.01 1 0.1 0.01 1 0.1 0.01 1 0.1 0.01 1 0.1 0.01 1 0.1 0.01 1 0.1 0.01
HSB-CT HSB-NT CPER
KS-BO KS-B120 LH-CF
LH-IF
S
(1, 0.1, 0.01)
Figure 4.6 Probability of stability of (a) “real” matrices and (b) “randomized” matrices for seven
different food webs whose diagonal terms were weighted by fixed values of s (1, 0.1, 0.01). CPER,
Central Plains Experimental Range (Colorado, United States); LH, Loevinkhoeve (the Netherlands);
IF, integrated farming; CF, conventional farming; HSB, Horseshoe Bend (Georgia, United States); CT,
conventional tillage; NT, no tillage; KS, Kjettslinge (Sweden); B0, without fertilizer; B120, with fertil-
izer. (From de Ruiter, Moore et al., 1993.)
the compartmentalized arrangement of species was more likely to be stable than a random
network of interactions of similar diversity and complexity. The soil food webs seem to
bear this out (Moore et al., 2004; Rooney et al., 2006). Simplified representations of energy
channels, one fast (e.g., a bacterial energy channel) and one slow (e.g., a fungal energy
channel), coupled by a predator revealed that the coupled systems were more stable than
either energy channel in isolation ( Figure  4.7 ) . Depending on the choice of parameters,
the coupled system was quite tolerant to changes or shifts in the relative amount of flux
through the fast or slow channel, but a tipping point or singularity in the dynamic states
was evident. It appears that unimpeded flow of material through either channel has its
limits, leading to instability.
The analyses presented effectively altered the energetic organization of the commu-
nity by the redistribution of the biomass and directional flow of matter within the system.
The adjustments to the paired interactions' strengths that de Ruiter et al. (1995) made nec-
essarily moved biomass to higher trophic positions. The adjustment to the directional flow
of material through different channels implied an alteration in the relative abundance of
basal resources (bacteria or fungi). Given the steady-state assumptions, these alterations
in effect implied that greater enrichment rates in the form of plant production or detritus
were in play to support the biomass at the higher trophic positions.
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