Environmental Engineering Reference
In-Depth Information
Figure 6.2.
Illustration of the direct lines of dependency (solid arrows) among preda-
tor and prey species in the California sage-scrub food web examined by Crooks and
Soulé (1999). The directions of the arrows indicate the direction of a species effect on
another species. The minus sign indicates that a species has a detrimental effect on the
abundance of another species.The plus sign indicates that a species has a positive effect
on the population of another species. The dashed arrow indicates an indirect effect, an
emergent property of food webs that arises when two remote species are connected by
their common interaction with an intermediate species. Such emergent indirect effects
are what create complexity in ecological systems by linking many species together in
myriad ways. The implication of such interconnectedness is that disturbances do not
necessarily affect a few species:Their effects can reverberate throughout the food web.
