Environmental Engineering Reference
In-Depth Information
Thus, there are two kinds of com-
petitive interactions. The first, in
which species directly interfere with
each other's ability to access re-
sources, is known as contest or inter-
ference competition. The second
form of competition is indirect and
results from a mutual effort to exploit
the greatest share of a common re-
source, called scramble or exploitative
competition.
There are two kinds of competitive
interactions. The first, in which
species directly interfere with each
other's ability to access resources,
is known as contest or interference
competition. The second form of
competition is indirect and results
from a mutual effort to exploit the
greatest share of a common re-
source, called scramble or exploita-
tive competition.
Conceptualizing Complexity: Direct
Effects, Indirect Effects, and
Species Diversity
The advantage of conceptualizing species interactions in terms of the cou-
plets or triplets depicted in figure 2.1 is that we can assemble more com-
plex structures by combining different couplets and triplets. For example,
we could combine two consumer-resource couplets to create a linear, three-
trophic-level food chain comprised of a top carnivore, a herbivore, and a
plant species (figure 2.2a).We could build more branching systems by com-
bining the basic exploitative competition triplet with two additional con-
sumer-resource links to create a system in which two consumers each have
exclusive access to a resource and share a common third resource (figure
2.2b).We could add a consumer link to an interference competition sys-
tem such that a superior competitor is also more vulnerable to predation
than a weaker competitor (figure 2.2c), called consumer-mediated compe-
tition.Alternatively, we could add two consumer links to two sets of inter-
ference competition systems (figure 2.2d) resulting in a trophically-mediated
interference competition system.
The food web diagrams help to understand additional, important prop-
erties of species interactions in ecosystems. First, species diversity may arise
as a consequence of many different dependencies or interactions. Second,
whenever more than two species are linked together by direct consumer-
resource or competitive interactions, we see the emergence of an indirect
effect in which the middle species mediates the nature and strength of ef-
fect of the first species on the third species.