Top-down effects of a predatory odonate dominate population, community and ecosystem processes in bromeliads

Background/Question/Methods

Predation is ubiquitous in natural systems, but there has been longstanding debate within ecology as to its importance to trophic levels other than the immediate prey, and to rates of nutrient and carbon flux within ecosystems. Here I synthesize a decade of experimental evidence that shows that a dominant predator in Costa Rican water-filled bromeliads, the odonate Mecistogaster modesta, has pervasive effects on the entire food web and broader ecosystem. Specifically, I examine the effects of this predator on detrital decomposition and other ecosystem functions, microfaunal densities and diversity, nitrogen flux into bromeliad tissue, and species colonization and emergence rates.   These predator effect sizes are compared to those of detritivore composition or presence, and overall effects estimated using meta-analysis statistics.

Results/Conclusions

In general, the effect of M. modesta on the measured community and ecosystem variables was much greater than that of detritivore composition or presence. Odonates significantly reduced decomposition rates but facilitated nutrient uptake by bromeliads, led to reduced diversity of ciliates and invertebrates, and reduced both colonization and emergence rates of detritivores. These results are explained by several traits of this odonate species, including its generalized diet and long larval stage relative to that of its prey.