COS 37-3 - Efficient energy transfer strengthens trophic cascades

Abstract: Trophic cascades are important determinants for food web dynamics and functioning. Despite many previous attempts have been made to reveal factors influencing the strength of trophic cascades, its ultimate mechanisms remain elusive. Potentially, two key food web processes may provide explanations for variations in trophic cascades. The first is that productivity determines trophic cascades as it provides basal resources for higher trophic levels (the productivity hypothesis); the second is the energy transfer efficiency accounts for changes in trophic cascade strength because it strongly determines the biomass distribution of the whole food web (energy transfer efficiency hypothesis).



Here we apply both mesocosm experiment and mathematical models to test the above two hypothesis. Specifically, we applied a phytoplankton-zooplankton-shrimp food web for the mesocosm experiment, and simultaneously manipulated nutrient (i.e., phosphorus) input and zooplankton community composition to create variations in primary productivity and energy transfer efficiencies. In addition, we created three trophic level food chain models with multiple scenarios, e.g., varied assimilation efficiencies vs. fixed assimilation efficiencies, to generalize the results to more general scenarios.



Our experimental results showed that rather than primary productivity, predator efficiency strongly determines trophic cascade strength with a positive correlation was found. The productivity hypothesis is therefore rejected but the energy transfer efficiency hypothesis is confirmed. These findings further corroborate our modelling results. Our study advocates the integration energy transfer and trophic cascades, and further suggests the importance of an energetic perspective in ecological managements.