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Longer and less overlapping food webs in anthropogenically disturbed marine ecosystems: confirmations from the past.

Saporiti F, Bearhop S, Silva L, Vales DG, Zenteno L, Crespo EA, Aguilar A, Cardona L - PLoS ONE (2014)

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Animal Biology and Institut de Recerca de la Biodiversitat (IRBio), Faculty of Biology, University of Barcelona, Barcelona, Spain.

ABSTRACT
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.

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Isotopic niches/resource use areas of the species/functional groups described in the text and calculated with the standard ellipse areas corrected for small sample size (SEAC) over time in the two geographical areas.a) Central-northern Patagonia and b) Southern Patagonia. Herbivores = mussels and limpets; Aa = South American fur seals; Of = South American sea lions; Sm = Magellanic penguins.
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pone-0103132-g002: Isotopic niches/resource use areas of the species/functional groups described in the text and calculated with the standard ellipse areas corrected for small sample size (SEAC) over time in the two geographical areas.a) Central-northern Patagonia and b) Southern Patagonia. Herbivores = mussels and limpets; Aa = South American fur seals; Of = South American sea lions; Sm = Magellanic penguins.

Mentions: The structures of the five food webs analysed are shown in Figure 2. The δ15N values of herbivores decreased from past to present (Table 4) both in central-northern Patagonia (Wilcoxon-Mann-Whitney test: W = 3, p<0.001) and in southern Patagonia (ANOVA: F2,32 = 24.7, p<0.01). Likewise the δ13C values of ancient herbivores from southern Patagonia differed from the modern ones (ANOVA: F2,32 = 5.42, p<0.01) but changes were not statistically significant in central-northern Patagonia (t-test: t = −0.09, df = 16.777, p = 0.93). These results demonstrate that the isotopic baseline may change dramatically throughout time and allow us to properly interpret the structure of the ancient food webs.


Longer and less overlapping food webs in anthropogenically disturbed marine ecosystems: confirmations from the past.

Saporiti F, Bearhop S, Silva L, Vales DG, Zenteno L, Crespo EA, Aguilar A, Cardona L - PLoS ONE (2014)

Isotopic niches/resource use areas of the species/functional groups described in the text and calculated with the standard ellipse areas corrected for small sample size (SEAC) over time in the two geographical areas.a) Central-northern Patagonia and b) Southern Patagonia. Herbivores = mussels and limpets; Aa = South American fur seals; Of = South American sea lions; Sm = Magellanic penguins.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4116168&req=5

pone-0103132-g002: Isotopic niches/resource use areas of the species/functional groups described in the text and calculated with the standard ellipse areas corrected for small sample size (SEAC) over time in the two geographical areas.a) Central-northern Patagonia and b) Southern Patagonia. Herbivores = mussels and limpets; Aa = South American fur seals; Of = South American sea lions; Sm = Magellanic penguins.
Mentions: The structures of the five food webs analysed are shown in Figure 2. The δ15N values of herbivores decreased from past to present (Table 4) both in central-northern Patagonia (Wilcoxon-Mann-Whitney test: W = 3, p<0.001) and in southern Patagonia (ANOVA: F2,32 = 24.7, p<0.01). Likewise the δ13C values of ancient herbivores from southern Patagonia differed from the modern ones (ANOVA: F2,32 = 5.42, p<0.01) but changes were not statistically significant in central-northern Patagonia (t-test: t = −0.09, df = 16.777, p = 0.93). These results demonstrate that the isotopic baseline may change dramatically throughout time and allow us to properly interpret the structure of the ancient food webs.

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Animal Biology and Institut de Recerca de la Biodiversitat (IRBio), Faculty of Biology, University of Barcelona, Barcelona, Spain.

ABSTRACT
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.

Show MeSH
Related in: MedlinePlus