Predator diversity and functional traits influence community structure and ecosystem processes

Background/Question/Methods

Past research has shown that the direct and indirect effects of different predator species on community composition and structure are not identical, and can differ with respect to predator functional traits. Predator/prey interactions that generate effects that transcend the biotic elements of an ecosystem may help us better predict species influences on ecosystem function. It is poorly understood, however, how differing predator traits influence ecosystem function. The main objective of our study was to examine how predator diversity influences community and ecosystem variables within bromeliads. Here, we compared the joint and combined effects of an active predatory adult dytiscid, Copelatus sp., and a sit-and-pursue predatory odonate lavae, Mecistogaster modesta, on aquatic detritivore abundance, insect emergence and dispersal, leaf litter decomposition, and dissolved organic carbon ([TOC]), total nitrogen ([TN]), and CO₂ ([CO₂]) concentrations within bromeliad mesocosms. Linear and generalized linear models were used to test differences between predator and control treatments. In situations when either predator type differed from controls, orthoganol contrasts were carried out to see if they differed from one another.

Results/Conclusions

At the community level, Copelatus and M. modesta treatments had significantly lower detritivore abundances and fewer insect emergences than control treatments. Predator type, however, was only significantly different for detritivore abundance. Here, M. modesta had lower detritivore abundance compared to Copelatus treatments. For insect dispersal, only M. modesta was significantly different from control treatments and there were no differences between predator types. At the ecosystem level, both predators had significantly lower leaf litter decomposition compared to control treatments. However, only M. modesta had significantly lower [TOC], [CO₂], and [TN] compared to controls. Predator type, however, was only significantly different for leaf litter decomposition, [TOC], and [CO₂]. For these three variables, M. modesta were lower compared to Copelatus treatments. Predator diversity had non-additive antagonistic effects on all community variables and leaf litter decomposition. Predator diversity only had additive effects in cases where Copelatus treatments were not different than control treatments. This study shows that within bromeliads, M. modesta larvae have greater effects on community and ecosystem variables compared to adult Copelatus. This study suggests that predator functional traits and the interplay among predators may be important variables to consider when predicting species effects on communities and ecosystem function.