Network Utility Analysis: A Non-Thermodynamic Constraint to Trophic Transfer Efficiency

The efficiency of resource transfer between trophic levels in an ecosystem tend to be relatively low in spite of the considerable amount of time organisms have had to evolve uptake and assimilation processes. In fact, a general rule of thumb in ecology is that only about 10 percent of the total energy intake into an organism is transferred up to the next trophic level. In addition to the thermodynamic, physical, and chemical limitations, our research indicates another possible limitation to trophic transfer efficiency. Utility analysis, a resource-based input-output measure of the overall usefulness a component's flow has on the entire system, is used to identify the qualitative and the quantitative relations in a model. For simple systems, utility is dependent on transfer efficiencies, and in more complex models with feedback and cycling, the relative net transfer efficiency is used. For utility to be calculable, the matrix of direct utility must meet a convergent criterion. However, when these efficiencies are too large this criterion is not met. This is interpreted to mean that utility, which is inherently positive, is not conveyed within these systems. This paper shows, for simple food chain models, where the breakdown in utility analysis occurs and what patterns exist as systems approach this threshold. Although computable utility may not be a necessary condition for low trophic efficiency, it may be sufficient to explain low transfer efficiencies in in constituted ecosystems.