MODELLING THE RELATIONSHIP BETWEEN A PITCHER PLANT ( SARRACENIA PURPUREA) AND ITS PHYTOTELMA COMMUNITY: MUTUALISM OR PARASITISM?

Mouquet N., Daufresne T., Gray S.M., and Miller T.E. (2008).

Functional Ecology, doi:10.1111/j.1365-2435.2008.01421.x

Key message : To improve our understanding of the relationship between the pitcher plant (Sarracenia purpurea) and the phytotelma community inhabiting its leaves we built an exploratory, mechanistic model based on stochiometric constraints on carbon and nitrogen associated with prey decomposition. Our theoretical results suggest that the phytotelma community is acting as a mineralizing system producing nitrogen for the plant. In our model, nitrogen yield is higher if the phytotelma community is restricted to bacteria alone than when the full food web is present. Nitrogen availability is negatively affected by bacterivores (rotifers and protozoa mostly) and positively affected by a cascading effect of mosquito larvae. When sedimentation rate is high, mosquitoes have a global positive effect on nitrogen production because they indirectly reduce the amount of nitrogen lost through sedimentation more than they export nitrogen through pupation. On the other hand, when sedimentation rate is low there is a hump-shaped relationship between the uptake rate of bacterivores by mosquito larvae and the nitrogen yield in the plant. We conclude that plant–bacteria and plant–mosquito interactions are predominantly mutualistic, whereas plant–bacterivore interactions are predominantly parasitic.