(B) Average difference in the body masses of resource and consumer species
at the bottom two and top two trophic levels for each system type.
Toxin resistance confers significant advantages to consumer species
and has been observed in a wide range of herbivores and predators intimately involved with chemically defended prey (Brodie and Brodie, 1990; Mauricio et al., 1997; Gardner and Agrawal, 2002; Hartl and Baldwin, 2006; Hwang et at., 2007).
The model describes consumer growth and seeks conditions under which individuals of both consumer species
can exhibit non-negative growth.
In these circumstances (which pertain to many taxa), the effect of trophic rank on the species - area relationship should be magnified, because an obligate generalist consumer species
will be absent unless each of its required resource types is present.
These two possibilities will be examined in a later study; both allow two consumer species
to coexist in the absence of a predator, and addition of the predator may actually prevent coexistence.
- We constructed microcosms that contained autotrophs, decomposers, and dead organic and inorganic nutrients and varied the number of consumer species
stocked in each microcosm.
Although the univariate tests showed no significant response of species C to any of the four consumer species
, Colpoda slightly reduced its mean density, while the other three consumers caused the mean density of this bacterium to increase slightly.
1) The additional resource exploitation as the result of an added consumer species
reduces total resource abundance for one or more resident consumer species
, favoring similar (i.e., parallel) changes in characteristics related to resource use (Abrams 1986a, 1987a).
An example illustrating this is given in Table 2, in which species are drawn from a pool of 5 basal and 10 consumer species
. Those extinctions that do take place are among the species previously resident in the community [i.e., from the set [Mathematical Expression Omitted]]; the invader itself always remains.
Similarly, the basic principles described for competition for two resources can also be used to examine interaction involving a single resource and a predator on an intermediate consumer species
(Holt et al.
To complete the trophic chain, we now consider a consumer species
i + 1 feeding on species i.