Environmental Engineering Reference
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Figure 2.2. Complex food web structures assembled by linking combinations of the
couplets or triplets presented in figure 5.1. (a) A three-level food chain in which a car-
nivore (C) directly feeds on an herbivore (H) that directly feeds on a plant (P).The car-
nivore has an indirect beneficial affect on the plant (dashed line) by virtue of suppress-
ing the abundance of the herbivores eating plants. (b) A competitive system in which two
consumer species (C) vie for a shared resource (S) and consume mutually exclusive (E)
resources. (c) A system in which the abundance of a competitively dominant species (S 1 )
is controlled by a consumer species (C) thereby releasing less competitive species (S 2 and
S 3 ) from domination. Consequently, the consumer has an indirect, beneficial affect on
the less competitive species. (d) A multi-trophic variation of (c) in which a top predator
(P) alters herbivore foraging and abundance on dominant and subordinate competitor
species thereby introducing a host of indirect effects.
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