1. While much is known about the independent effects of trophic structure and temperature on
density and ecosystem processes, less is known about the interaction(s) between the two.
2. We manipulated the temperature of laboratory-based bacteria-protist communities that
contained communities with one, two, or three trophic levels, and recorded species’ densities and
3. Temperature, food chain length and their interaction produced significant responses in microbial
density and bacterial decomposition. Prey and resource density expressed different patterns of
temperature dependency during different phases of population dynamics. The addition of a predator
altered the temperature-density relationship of prey, from a unimodal trend to a negative one.
Bacterial decomposition was greatest in the presence of consumers at higher temperatures.
4. These results are qualitatively consistent with a recent model of direct and indirect temperature
effects on resource-consumer population dynamics. Results highlight and reinforce the importance
of indirect effects of temperature mediated through trophic interactions. Understanding and predicting
the consequences of environmental change will require that indirect effects, trophic structure,
and individual species’ tolerances be incorporated into theory and models.