Figure 1.
Path models ( = a priori hypotheses) describing decomposition dynamics in the Sarracenia food web.
(A) The sampling effect model tests if high species richness increases the probability that an ‘important’ decomposer will be present. This model was run for each species to determine if any one species contributes disproportionately to decomposition. (B) The indirect top-down cascade model tests if mosquitoes, copepods, and rotifers indirectly facilitate bacterial decomposition by releasing bacteria from predation by protozoa (dashed lines). (C) The combined top-down cascade model tests if the indirect effects (dashed lines) from mosquitoes, copepods, and rotifers along with direct predation (solid lines) on bacteria alter decomposition. The indirect (D) and combined (E) full food web models include paths for predation by the mite (Sarraceniopus gibsoni) on bacteria and the direct decomposition by the midge (Metriocnemus knabi) as pathways that influence decomposition in addition to the pathways in models (B) and (C) respectively.
Figure 2.
Relationship between final species richness, final trophic diversity (TD), and decomposition.
Decomposition showed a ‘hump-shaped’, polynomial relationship with species richness (A) and a positive linear relationship with TD (B). Regression models (lm in R v.2.11.1) are significant at P<0.05.
Figure 3.
Best-fit path models describing decomposition dynamics in the Sarracenia food web.
The indirect full food web model including ant mass (A) was the top overall model and the midge sampling effect model including ant mass (B) was the top sampling effect path model explaining decomposition by bacteria (Decomp) in the Sarracenia food web. Standardized path coefficients are shown for each link and arrows are proportional to the magnitude of the coefficient. Solid black lines indicate significant (P<0.05) positive relationships and solid red lines indicate significant negative relationships. Dashed lines indicate non-significant relationships. The R2 value shows the amount of variation in decomposition explained by the path model.
Table 1.
Best-fit food web and sampling effect path models for decomposition in the Sarracenia food web.