Community-wide impacts of interactive trait-mediated interactions

Background/Question/Methods

Recent literature in trait-mediated indirect interactions (TMIIs) suggests that the incorporation of multiple TMIIs in ecological communities can have significant impacts on population and community dynamics. Among them, a few empirical examples emphasize the importance of two interacting TMIIs that cascade the effect of a remote species from a food chain to consumer-resource dynamics of a lateral food chain. In a neotropic food web in a coffee agroecosystem, an ant (Azteca serieasur) and its parasitic phorid fly (Pseudacteon laciniosus), form this structure and importantly regulate the population dynamics of a predatory beetle (Azya orbigera) of the ant’s mutualistic partner, the green coffee scale (Coccus viridis). The ant interferes with beetle adults and the parasitoid wasp of the beetle larvae, forming the first-tiered TMII. This interference, however, is interrupted by the induced defensive behavior of the ant by the phorid fly, the second-tiered TMII.  The consequences are increased feeding, oviposition and parasitism rates and a female-biased sex ratio of the beetle. As the interactive effect of the ant and the phorid fly is evident at the population level, it is unclear whether this effect has a broader community-wide implication.

Results/Conclusions

We sampled insects at two coffee agroecosystems in Neotropics before and after the induction of the interactive trait-mediated indirect interactions. We identified trapped insects to orders and morphospecies. We then applied generalized linear models to determine whether farm and treatment (with/without interactive TMIIs) have effects on species abundance, richness and Simpson’s index of biodiversity. We then converted the coefficients obtained from the best models to derive effect sizes (log ratios) of farm and treatment. The results suggest that the interactive TMIIs increase species richness, abundance and biodiversity of Coleopteran insects in one of the farms, and decrease species abundance of Hemipteran insects in both of the farms. The rest do not show strong significant responses to the treatment. These results suggest that the interactive TMIIs would be important in regulating community dynamics in neotropic coffee agroecosystems.