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Phytophagous
Nematodes
Collembolans
Predaceous
Mites
Cryptostigmatic
Mites
Mycorrhizae
Roots
Nematode
Feeding Mites
Noncrypto-
stigmatic Mites
Saprophytic
Fungi
Predaceous
Nematodes
Fungivorous
Nematodes
Resistant
Detritus
Omnivorous
Nematodes
Labile
Detritus
Flagellates
Bacteria
Amoebae
Bacteriophagous
Nematodes
g Cm
2
yr
-1
<0.1
>0.1
>1.0
>10
>100
>1000
Figure 4.2
The energy flux description expressed in terms of carbon (g C m
2
y
−1
) of the shortgrass
steppe soil food web from the Central Plains Experimental Range (CPER), Nunn, Colorado. The
thickness of the vectors is scaled to the estimated carbon fluxes (g C m
2
y
−1
) among prey to predator
functional groups. Although not represented in this energy flux description, the boxes for func-
tional groups could be sized to scale to the standing biomass (g C m
2
) for each functional group as
well (see Moore, J.C., D.E. Walter, and H.W. Hunt. 1988. Arthropod regulation of micro- and meso-
biota in below-ground detrital food webs.
Annual Review of Entomology
33:419-439).
4.2.3
The functional food web
A functional food web can be derived from (a) the connectedness web, (b) the set of differ-
ential equations that include the trophic interactions among species to describe the popu-
lation dynamics of the species, and (c) energy flux descriptions. The functional description
displays impacts that each population (species or functional groups) has on the dynamics
of themselves and the other species in the food web. We have adopted interaction strength
as the metric to represent these impacts (
Figure 4.4
).
There are several different definitions of interaction strength in the literature (Paine,
1992; Berlow et al., 2004). We define interaction strength in terms of the elements of the
Jacobian matrix of the system of differential equations that describe the dynamics of the
food web. For example, we could use the following set of equations to describe an
n
-spe-
cies community:
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