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Small but powerful: top predator local extinction affects ecosystem structure and function in an intermittent stream.

Rodríguez-Lozano P, Verkaik I, Rieradevall M, Prat N - PLoS ONE (2015)

Bottom Line: We found that top predator absence led to 'mesopredator release', and also to 'prey release' despite intraguild predation, which contrasts with traditional food web theory.Regarding ecosystem function, periphyton primary production decreased in apex consumer absence.In this study, the apex consumer was functionally irreplaceable; its local extinction led to the loss of an important functional role that resulted in major changes to the ecosystem's structure and function.

View Article: PubMed Central - PubMed

Affiliation: Freshwater Ecology and Management (F.E.M.) Research Group, Departament d'Ecologia, Facultat de Biologia, Universitat de Barcelona, Barcelona, Spain.

ABSTRACT
Top predator loss is a major global problem, with a current trend in biodiversity loss towards high trophic levels that modifies most ecosystems worldwide. Most research in this area is focused on large-bodied predators, despite the high extinction risk of small-bodied freshwater fish that often act as apex consumers. Consequently, it remains unknown if intermittent streams are affected by the consequences of top-predators' extirpations. The aim of our research was to determine how this global problem affects intermittent streams and, in particular, if the loss of a small-bodied top predator (1) leads to a 'mesopredator release', affects primary consumers and changes whole community structures, and (2) triggers a cascade effect modifying the ecosystem function. To address these questions, we studied the top-down effects of a small endangered fish species, Barbus meridionalis (the Mediterranean barbel), conducting an enclosure/exclosure mesocosm experiment in an intermittent stream where B. meridionalis became locally extinct following a wildfire. We found that top predator absence led to 'mesopredator release', and also to 'prey release' despite intraguild predation, which contrasts with traditional food web theory. In addition, B. meridionalis extirpation changed whole macroinvertebrate community composition and increased total macroinvertebrate density. Regarding ecosystem function, periphyton primary production decreased in apex consumer absence. In this study, the apex consumer was functionally irreplaceable; its local extinction led to the loss of an important functional role that resulted in major changes to the ecosystem's structure and function. This study evidences that intermittent streams can be affected by the consequences of apex consumers' extinctions, and that the loss of small-bodied top predators can lead to large ecosystem changes. We recommend the reintroduction of small-bodied apex consumers to systems where they have been extirpated, to restore ecosystem structure and function.

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Barbus meridionalis density effects on macroinvertebrate abundance and rarefied richness for primary and secondary consumers.Barbus meridionalis density effects on macroinvertebrate abundance (mean ± SE individuals m-2) and rarefied taxa richness (mean ± SE rarefied taxa sample-1) for: (a-b) primary consumers, (c-d) secondary consumers, and (e-f) the ratio of secondary to primary consumers (mean ± SE ratio sample-1). Red bars = treatment without barbels; yellow bars = treatment with a low density of barbels; blue bars = treatment with a high density of barbels. Different letters correspond to significant differences resulting from the pairwise comparisons among treatments (U-test, p<0.05).
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pone.0117630.g004: Barbus meridionalis density effects on macroinvertebrate abundance and rarefied richness for primary and secondary consumers.Barbus meridionalis density effects on macroinvertebrate abundance (mean ± SE individuals m-2) and rarefied taxa richness (mean ± SE rarefied taxa sample-1) for: (a-b) primary consumers, (c-d) secondary consumers, and (e-f) the ratio of secondary to primary consumers (mean ± SE ratio sample-1). Red bars = treatment without barbels; yellow bars = treatment with a low density of barbels; blue bars = treatment with a high density of barbels. Different letters correspond to significant differences resulting from the pairwise comparisons among treatments (U-test, p<0.05).

Mentions: When we analysed macroinvertebrate communities separately for primary and secondary consumers, we detected that B. meridionalis density affected primary consumer abundance (χ2 = 7.38, p = 0.025; Fig. 4A) but not primary consumer richness (χ2 = 1.19, p = 0.55) or rarefied richness (χ2 = 1.42, p = 0.49; Fig. 4B). Top predator absence increased secondary consumer abundance (χ2 = 12.49, p = 0.002; Fig. 4C) and richness before (χ2 = 12.89, p = 0.002) and after rarefaction (χ2 = 8.17, p = 0.017; Fig. 4D). The ratio for predator:prey abundance marginally increased (abundance: χ2 = 5.40, p = 0.07, Fig. 4E) in the absence of barbels, whereas the ratio for predator:prey richness increased significantly (richness: χ2 = 12.00, p = 0.002; rarefied richness: χ2 = 9.92, p = 0.007; Fig. 4F).


Small but powerful: top predator local extinction affects ecosystem structure and function in an intermittent stream.

Rodríguez-Lozano P, Verkaik I, Rieradevall M, Prat N - PLoS ONE (2015)

Barbus meridionalis density effects on macroinvertebrate abundance and rarefied richness for primary and secondary consumers.Barbus meridionalis density effects on macroinvertebrate abundance (mean ± SE individuals m-2) and rarefied taxa richness (mean ± SE rarefied taxa sample-1) for: (a-b) primary consumers, (c-d) secondary consumers, and (e-f) the ratio of secondary to primary consumers (mean ± SE ratio sample-1). Red bars = treatment without barbels; yellow bars = treatment with a low density of barbels; blue bars = treatment with a high density of barbels. Different letters correspond to significant differences resulting from the pairwise comparisons among treatments (U-test, p<0.05).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4340793&req=5

pone.0117630.g004: Barbus meridionalis density effects on macroinvertebrate abundance and rarefied richness for primary and secondary consumers.Barbus meridionalis density effects on macroinvertebrate abundance (mean ± SE individuals m-2) and rarefied taxa richness (mean ± SE rarefied taxa sample-1) for: (a-b) primary consumers, (c-d) secondary consumers, and (e-f) the ratio of secondary to primary consumers (mean ± SE ratio sample-1). Red bars = treatment without barbels; yellow bars = treatment with a low density of barbels; blue bars = treatment with a high density of barbels. Different letters correspond to significant differences resulting from the pairwise comparisons among treatments (U-test, p<0.05).
Mentions: When we analysed macroinvertebrate communities separately for primary and secondary consumers, we detected that B. meridionalis density affected primary consumer abundance (χ2 = 7.38, p = 0.025; Fig. 4A) but not primary consumer richness (χ2 = 1.19, p = 0.55) or rarefied richness (χ2 = 1.42, p = 0.49; Fig. 4B). Top predator absence increased secondary consumer abundance (χ2 = 12.49, p = 0.002; Fig. 4C) and richness before (χ2 = 12.89, p = 0.002) and after rarefaction (χ2 = 8.17, p = 0.017; Fig. 4D). The ratio for predator:prey abundance marginally increased (abundance: χ2 = 5.40, p = 0.07, Fig. 4E) in the absence of barbels, whereas the ratio for predator:prey richness increased significantly (richness: χ2 = 12.00, p = 0.002; rarefied richness: χ2 = 9.92, p = 0.007; Fig. 4F).

Bottom Line: We found that top predator absence led to 'mesopredator release', and also to 'prey release' despite intraguild predation, which contrasts with traditional food web theory.Regarding ecosystem function, periphyton primary production decreased in apex consumer absence.In this study, the apex consumer was functionally irreplaceable; its local extinction led to the loss of an important functional role that resulted in major changes to the ecosystem's structure and function.

View Article: PubMed Central - PubMed

Affiliation: Freshwater Ecology and Management (F.E.M.) Research Group, Departament d'Ecologia, Facultat de Biologia, Universitat de Barcelona, Barcelona, Spain.

ABSTRACT
Top predator loss is a major global problem, with a current trend in biodiversity loss towards high trophic levels that modifies most ecosystems worldwide. Most research in this area is focused on large-bodied predators, despite the high extinction risk of small-bodied freshwater fish that often act as apex consumers. Consequently, it remains unknown if intermittent streams are affected by the consequences of top-predators' extirpations. The aim of our research was to determine how this global problem affects intermittent streams and, in particular, if the loss of a small-bodied top predator (1) leads to a 'mesopredator release', affects primary consumers and changes whole community structures, and (2) triggers a cascade effect modifying the ecosystem function. To address these questions, we studied the top-down effects of a small endangered fish species, Barbus meridionalis (the Mediterranean barbel), conducting an enclosure/exclosure mesocosm experiment in an intermittent stream where B. meridionalis became locally extinct following a wildfire. We found that top predator absence led to 'mesopredator release', and also to 'prey release' despite intraguild predation, which contrasts with traditional food web theory. In addition, B. meridionalis extirpation changed whole macroinvertebrate community composition and increased total macroinvertebrate density. Regarding ecosystem function, periphyton primary production decreased in apex consumer absence. In this study, the apex consumer was functionally irreplaceable; its local extinction led to the loss of an important functional role that resulted in major changes to the ecosystem's structure and function. This study evidences that intermittent streams can be affected by the consequences of apex consumers' extinctions, and that the loss of small-bodied top predators can lead to large ecosystem changes. We recommend the reintroduction of small-bodied apex consumers to systems where they have been extirpated, to restore ecosystem structure and function.

Show MeSH
Related in: MedlinePlus