Food-density-dependent inefficiency in animals with a gut as a stabilizing mechanism in trophic dynamics.

Animals with a gut, when confronted with food supplied ad libitum, can elevate their ingestion rates and inefficiently use the material they ingest. As a consequence, assimilation efficiency (AE) declines, resulting in food-density-dependent inefficiency (f-DDI). A model describing these processes shows that f-DDI can dampen the consequences of oscillations in food abundance that may occur in response to external stochastic (e.g. climatic) forcing both with respect to production and timing. This response is illustrated with a simple planktonic food chain of a phytoplankter and two consumers. The assumption of a fixed gut transit time, consistent with the traditional model descriptions of a fixed AE, produces predator-prey oscillations. By contrast, simulations using a model showing f-DDI (behaving in accordance with the experimental data) cushion not only the impact of such oscillations but also the effects of the removal of intermediate grazers in the food chain. The operation of f-DDI affects other trophic interactions through changes in the nutrient regeneration and the voiding rates. The extent to which f-DDI operates in nature needs valuation, followed by the appropriate construction of consumer-based ecosystem models.