Community Ecology Processes, Models, and Applications

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