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A mechanistic theory for aquatic food chain length.

ABSTRACT: Multiple hypotheses propose an ostensibly disparate array of drivers of food chain length (FCL), with contradictory support from natural settings. Here we posit that the magnitude of vertical energy flux in food webs underlies several drivers of FCL. We show that rising energy flux fuels top-heavy biomass pyramids, promoting omnivory, thereby reducing FCL. We link this theory to commonly evaluated hypotheses for environmental drivers of FCL (productivity, ecosystem size) and demonstrate that effects of these drivers should be context-dependent. We evaluate support for this theory in lake and marine ecosystems and demonstrate that ecosystem size is the most important driver of FCL in low-productivity ecosystems (positive relationship) while productivity is most important in large and high-productivity ecosystems (negative relationship). This work stands in contrast to classical hypotheses, which predict a positive effect of productivity on FCL, and may help reconcile the contradictory nature of published results for drivers of FCL.

SUBMITTER: Ward CL

PROVIDER: S-EPMC5725575 | biostudies-literature | 2017 Dec

REPOSITORIES: biostudies-literature

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A mechanistic theory for aquatic food chain length.

Ward Colette L CL McCann Kevin S KS

Nature communications 20171211 1

Multiple hypotheses propose an ostensibly disparate array of drivers of food chain length (FCL), with contradictory support from natural settings. Here we posit that the magnitude of vertical energy flux in food webs underlies several drivers of FCL. We show that rising energy flux fuels top-heavy biomass pyramids, promoting omnivory, thereby reducing FCL. We link this theory to commonly evaluated hypotheses for environmental drivers of FCL (productivity, ecosystem size) and demonstrate that eff ...[more]

PMID: 29229910

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Project description:Abstract Aquatic and their adjacent terrestrial ecosystems are linked via the flux of organic and inorganic matter. Emergent aquatic insects are recognized as high‐quality food for terrestrial predators, because they provide more physiologically relevant long‐chain polyunsaturated fatty acids (PUFA) than terrestrial insects. The effects of dietary PUFA on terrestrial predators have been explored mainly in feeding trials conducted under controlled laboratory conditions, hampering the assessment of the ecological relevance of dietary PUFA deficiencies under field conditions. We assessed the PUFA transfer across the aquatic–terrestrial interface and the consequences for terrestrial riparian predators in two outdoor microcosm experiments. We established simplified tritrophic food chains, consisting of one of four basic food sources, an intermediary collector gatherer (Chironomus riparius, Chironomidae), and a riparian web‐building spider (Tetragnatha sp.). The four basic food sources (algae, conditioned leaves, oatmeal, and fish food) differed in PUFA profiles and were used to track the trophic transfer of single PUFA along the food chain and to assess their potential effects on spiders, that is, on fresh weight, body condition (size‐controlled measurement of nutritional status), and immune response. The PUFA profiles of the basic food sources, C. riparius and spiders differed between treatments, except for spiders in the second experiment. The PUFA α‐linolenic acid (ALA, 18:3n‐3) and ɣ‐linolenic acid (GLA, 18:3n‐6) were major contributors to the differences between treatments. PUFA profiles of the basic food sources influenced the fresh weight and body condition of spiders in the first experiment, but not in the second experiment, and did not affect the immune response, growth rate, and dry weight in both experiments. Furthermore, our results indicate that the examined responses are dependent on temperature. Future studies including anthropogenic stressors would deepen our understanding of the transfer and role of PUFA in ecosystems. Aquatic and their adjacent terrestrial ecosystems are linked via the flux of organic and inorganic matter. We assessed the PUFA transfer across the aquatic‐terrestrial interface and the consequences for terrestrial riparian predators in outdoor microcosm experiments. We established simplified tritrophic food chains, consisting one basic food source, an intermediary collector gatherer (Chironomus riparius, Chironomidae), and a riparian web‐building spider (Tetragnatha sp.). The four basic food sources (algae, conditioned leaves, oatmeal, fish food) differed in PUFA profiles and were used to track the trophic transfer of single PUFA along the food chain and to assess their potential effects on spiders.

Dataset Information

A mechanistic theory for aquatic food chain length.

Publications

A mechanistic theory for aquatic food chain length.

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