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

ABSTRACT: 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.

SUBMITTER: Flynn KJ

PROVIDER: S-EPMC2679076 | biostudies-literature | 2009 Mar

REPOSITORIES: biostudies-literature

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

Flynn Kevin J KJ

Proceedings. Biological sciences 20090301 1659

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 ...[more]

PMID: 19129108

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Project description:Despite growing interest in ecological consequences of parasitism in food webs, relatively little is known about effects of parasites on long-term population dynamics of non-host species or about whether such effects are density or trait mediated. We studied a tri-trophic food chain comprised of (i) a bacterial basal resource (Serratia fonticola), (ii) an intermediate consumer (Paramecium caudatum), (iii) a top predator (Didinium nasutum) and (iv) a parasite of the intermediate consumer (Holospora undulata). A fully factorial experimental manipulation of predator and parasite presence/absence was combined with analyses of population dynamics, modelling and analyses of host (Paramecium) morphology and behaviour. Predation and parasitism each reduced the abundance of the intermediate consumer (Paramecium), and parasitism indirectly reduced the abundance of the basal resource (Serratia). However, in combination, predation and parasitism had non-additive effects on the abundance of the intermediate consumer, as well as on that of the basal resource. In both cases, the negative effect of parasitism seemed to be effaced by predation. Infection of the intermediate consumer reduced predator abundance. Modelling and additional experimentation revealed that this was most likely due to parasite reduction of intermediate host abundance (a density-mediated effect), as opposed to changes in predator functional or numerical response. Parasitism altered morphological and behavioural traits, by reducing host cell length and increasing the swimming speed of cells with moderate parasite loads. Additional tests showed no significant difference in Didinium feeding rate on infected and uninfected hosts, suggesting that the combination of these modifications does not affect host vulnerability to predation. However, estimated rates of encounter with Serratia based on these modifications were higher for infected Paramecium than for uninfected Paramecium. A mixture of density-mediated and trait-mediated indirect effects of parasitism on non-host species creates rich and complex possibilities for effects of parasites in food webs that should be included in assessments of possible impacts of parasite eradication or introduction.

Dataset Information

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

Publications

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

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