Longer and less overlapping food webs in anthropogenically disturbed marine ecosystems: confirmations from the past
Public Library of Science
© 2014 Saporiti et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
The human exploitation of marine resources is characterised by the preferential removal of the largest species. Although this is expected to modify the structure of food webs, we have a relatively poor understanding of the potential consequences of such alteration. Here, we take advantage of a collection of ancient consumer tissues, using stable isotope analysis and SIBER to assess changes in the structure of coastal marine food webs in the South-western Atlantic through the second half of the Holocene as a result of the sequential exploitation of marine resources by hunter-gatherers, western sealers and modern fishermen. Samples were collected from shell middens and museums. Shells of both modern and archaeological intertidal herbivorous molluscs were used to reconstruct changes in the stable isotopic baseline, while modern and archaeological bones of the South American sea lion Otaria flavescens, South American fur seal Arctocephalus australis and Magellanic penguin Spheniscus magellanicus were used to analyse changes in the structure of the community of top predators. We found that ancient food webs were shorter, more redundant and more overlapping than current ones, both in northern-central Patagonia and southern Patagonia. These surprising results may be best explained by the huge impact of western sealing on pinnipeds during the fur trade period, rather than the impact of fishing on fish populations. As a consequence, the populations of pinnipeds at the end of the sealing period were likely well below the ecosystem's carrying capacity, which resulted in a release of intraspecific competition and a shift towards larger and higher trophic level prey. This in turn led to longer and less overlapping food webs.
Fundacio´n BBVA funded this research as part of the project ‘‘Efectos de la explotacio´n humana sobre depredadores apicales y la estructura de la red tro´fica del Mar Argentino durante los u´timos 6000 an˜os’’ (BIOCON08-194/09 2009-2011). Agencia Nacional de Promocio´n Cientı´fica y Tecnolo´gica (Argentina) provided additional funding through the project ‘‘Ana´lisis del uso de los recursos tro´ficos y su relacio´n con cambios en la abundancia en tres predadores tope del Mar Argentino’’. FS has been supported by an FPU Fellowship granted by the Spanish Ministerio de Educacio´n, Cultura y Deporte (AP 2009- 4573). Half of the cost of the publication of this article has been funded by the University of Barcelona. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
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Vol. 9, e103132
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