mostly still for experimental communities. For
field studies, the life span of the organisms
involved is often too long compared with the
length of the study to unambiguously evaluate
stability, but recent studies deal with that problem.
Insights gained from the dynamics of specific food
web modules have increased over the last few
decades. But still the question remains how such
modules are organized together into complex in-
teraction webs, and how their interplay changes
theirdynamicsasobservedinisolatedmodules.
Therelativeimportanceofexternalforcingversus
internal dynamics for causing dynamics in food
webs under natural conditions is still hard to
assess. The study of the effects of climate change
and toxic pollutants on food webs makes it neces-
sary to concentrate in the future on the interplay of
internal feedbacks and external forcing. Interest-
ing lessons can be learned from the comparison of
the configuration and dynamics of food webs
under different external conditions, e.g. different
temperatures that lead to different primary pro-
ductivity.Wherestrongevidencefortheexistence
of trophic cascades initially came from aquatic
systems, terrestrial examples are now known.
New studies on the dynamics of complex interac-
tion webs have concentrated on the consequences
of specific patterning of interaction strengths
Predatory collembola
Collembola
Nematophagous mitesPredatory nematodes
Fungivorous nematodesPredatory nematodes
Fungivorous nematodes
Fungivorous nematodes
Predatory nematodes
Non-cryptostigmatic mitesCryptostigmatic mites
Fungivorous nematodes
Bacteriophagous nematodes
Bacteriophagous nematodes
Bacteriophagous nematodes
Phytophagous nematodes
Phytophagous nematodesPhytophagous nematodes
Phytophagous nematodesBacteria
Bacteria
BacteriaBacteria
Bacteria
Bacteria
Detritus
0.1 10
1 100 –40 –30 –20
per capita effect on prey
(mean = –7.6)
per capita effect on predator
(mean = 0.1)
–10 0 0 0.1 0.2 0.3
Basal resources
Trophic position
Resource Top predators Consumer
0.4 0.5 0102030405060
1000
Feeding rate
(kg ha–1 year–1)
Interaction strength
(year–1)
abc
Impact on stability
(%)
Detritus
Detritus
Roots
Flagellates
Flagellates
Fungi
FungiFungi
Fungi
Fungi
Amoebae
Bacteriophagous nematodes
Bacteriophagous mites
Predatory collembolaPredatory collembola
Predatory collembola
Collembola
Predatory collembola
Nematophagous mites
Nematophagous mitesNematophagous mites
Nematophagous mites
Predatory mites
Predatory mitesPredatory mites
Predatory mitesPredatory mites
Predatory mites
Predatory mitesPredatory mites
Predatory mites
Predatory mites
Predatory nematodesPredatory nematodes
Predatory nematodes
Predatory nematodesPredatory nematodes
Predatory nematodes
Cryptostigmatic mites
Non-cryptostigmatic mites
Fungivorous nematodes
Bacteriophagous nematodes
Phytophagous nematodes
Bacteria
Flagellates
Fungi
Amoebae
Amoebae
Bacteriophagous mitesEnchytraeids
Enchytraeids
Enchytraeids
Figure 2.8Feeding rates (a), interactions strengths (b) and impacts of the interactions on food web stability (c) arranged
according to trophic position in the soil food web of arable fields with conventional agricultural practices at the
Lovinkhoeve Experimental Farm in The Netherlands. From de Ruiteret al.(1995). Reprinted with permission from AAAS.
TROPHIC DYNAMICS OF COMMUNITIES 35