Integrating interaction modifications: ecology, evolution and ecosystem functions in a neotropic food web

Background/Question/Methods

Interaction modification occurs while the presence of a third species influences the interaction strength of two others.  Many aspects of interaction modification remain unknown.  There are few empirical studies on how multiple interaction modifications at different trophic levels jointly influence the effect of biodiversity on ecosystem functions.  Also, theory predicts that interaction modification has an influence on evolution/coevolution.  However, empirical evidence is insufficient, especially when interactions occur at higher trophic levels.  Conducting species presence/absence experiments in a community composed of two pair-wise host-parasitoid interactions, in which one host (Azteca sericeasur) and its Pseudacteon parasitoid fly both act as interaction modifications influencing the parasitism of the other host (Azya orbigera, a predatory beetle), we address the following questions: How does the interplay of two interaction modifications facilitate energy transfer across a food chain? How would the interplay of the interaction modifications affect the sex ratio of the beetle? How would they further influence the distribution of sex-related traits of a beetle population? We use an ANOVA to determine the effects of the interaction modifications, and develop mechanistic models to test the influences of interaction modifications on the sex ratio and the parasitism rate of the beetle.  

Results/Conclusions

The results of our study suggest that the interplay between two interaction modifications that function differently on a focal trophic link can increase energy transfer across trophic levels of a food chain.  The first interaction modification interferes with the parasitoid, while the interplay of the two interaction modifications facilitates the parasitoid.  Specifically, the presence of both interaction modifications mediates the preferential parasitism: while the parasitoid wasp prefers to parasitize female beetle larvae when there is no interaction modification, the sex ratio of beetles surviving from parasitism was reversed when the two interaction modifications are present.  Our previous study on chemical ecology suggests that only female beetles can capitalize on the chemical cues of the interplay of the two interaction modifications to oviposit in resource rich patches.  Our new findings, combined with the previous one, suggest that the interplay of interaction modifications jointly influence the population dynamics of the beetle and the distribution of its sex-related traits in a population.  These two studies show that interaction modifications can cascade to higher trophic levels and influence the population dynamics and evolution of the beetle, and influences its pest control effect.