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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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Macroinvertebrate abundance for eight common taxa in the three barbel treatments.Macroinvertebrate abundance for eight of the most abundant taxa (> 50 ind m-2 in the treatment lacking barbels) in the three treatments with varying B. meridionalis densities. Bars represent mean ± SE (individuals m-2). Graphs are sorted by taxa abundance: (a) Tanytarsus sp., (b) Zavrelimyia sp., (c) Habrophlebia sp., (d) Gyraulus sp., (e) Radix sp., (f) Chalcolestes viridis, (g) Stictonectes sp. and (h) Chaoborus sp. 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.g003: Macroinvertebrate abundance for eight common taxa in the three barbel treatments.Macroinvertebrate abundance for eight of the most abundant taxa (> 50 ind m-2 in the treatment lacking barbels) in the three treatments with varying B. meridionalis densities. Bars represent mean ± SE (individuals m-2). Graphs are sorted by taxa abundance: (a) Tanytarsus sp., (b) Zavrelimyia sp., (c) Habrophlebia sp., (d) Gyraulus sp., (e) Radix sp., (f) Chalcolestes viridis, (g) Stictonectes sp. and (h) Chaoborus sp. 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: Barbel presence reduced macroinvertebrate total density (χ2 = 9.09, p = 0.011); macroinvertebrate density declined almost by half (46.2%) in the treatment with high barbel density compared to the treatment that did not contain barbels (U = 12, p = 0.01). We did not detect significant differences among treatments in taxa richness (χ2 = 4.29, p = 0.12) or in the Simpson’s diversity index (χ2 = 0.77, p = 0.68). The density of the most abundant macroinvertebrate taxa declined when barbels were present, but vulnerability varied among prey (Fig. 3, S1 Table). We distinguished four patterns of abundance related to barbel density: i) a decrease in abundance proportional to barbel density for some taxa such as Habrophlebia sp. and Chalcolestes viridis (see Fig. 3C,F); ii) a sharp decrease in abundance at barbel presence (i.e., at both low and high barbel densities but not proportional to barbel presence) for other taxa (e.g., mobile predators Stictonectes sp. and Chaoborus sp.; see Fig. 3G-H); iii) a significant reduction in taxa abundance only at high barbel density treatment compared to the other treatments (e.g. Zavrelimyia sp.; see Fig. 3B); and iv) no change in abundance for other taxa irrespective of barbel densities (e.g., Gyraulus sp.; see Fig. 3D).


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)

Macroinvertebrate abundance for eight common taxa in the three barbel treatments.Macroinvertebrate abundance for eight of the most abundant taxa (> 50 ind m-2 in the treatment lacking barbels) in the three treatments with varying B. meridionalis densities. Bars represent mean ± SE (individuals m-2). Graphs are sorted by taxa abundance: (a) Tanytarsus sp., (b) Zavrelimyia sp., (c) Habrophlebia sp., (d) Gyraulus sp., (e) Radix sp., (f) Chalcolestes viridis, (g) Stictonectes sp. and (h) Chaoborus sp. 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.g003: Macroinvertebrate abundance for eight common taxa in the three barbel treatments.Macroinvertebrate abundance for eight of the most abundant taxa (> 50 ind m-2 in the treatment lacking barbels) in the three treatments with varying B. meridionalis densities. Bars represent mean ± SE (individuals m-2). Graphs are sorted by taxa abundance: (a) Tanytarsus sp., (b) Zavrelimyia sp., (c) Habrophlebia sp., (d) Gyraulus sp., (e) Radix sp., (f) Chalcolestes viridis, (g) Stictonectes sp. and (h) Chaoborus sp. 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: Barbel presence reduced macroinvertebrate total density (χ2 = 9.09, p = 0.011); macroinvertebrate density declined almost by half (46.2%) in the treatment with high barbel density compared to the treatment that did not contain barbels (U = 12, p = 0.01). We did not detect significant differences among treatments in taxa richness (χ2 = 4.29, p = 0.12) or in the Simpson’s diversity index (χ2 = 0.77, p = 0.68). The density of the most abundant macroinvertebrate taxa declined when barbels were present, but vulnerability varied among prey (Fig. 3, S1 Table). We distinguished four patterns of abundance related to barbel density: i) a decrease in abundance proportional to barbel density for some taxa such as Habrophlebia sp. and Chalcolestes viridis (see Fig. 3C,F); ii) a sharp decrease in abundance at barbel presence (i.e., at both low and high barbel densities but not proportional to barbel presence) for other taxa (e.g., mobile predators Stictonectes sp. and Chaoborus sp.; see Fig. 3G-H); iii) a significant reduction in taxa abundance only at high barbel density treatment compared to the other treatments (e.g. Zavrelimyia sp.; see Fig. 3B); and iv) no change in abundance for other taxa irrespective of barbel densities (e.g., Gyraulus sp.; see Fig. 3D).

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