Fig 1.
Diagram of the trophic interactions in intermittent stream food webs in the presence and absence of the apex consumer.
This diagram describes our two hypotheses related to apex consumer extirpation: a) ‘prey release’ hypothesis and b) ‘mesopredator release’ hypothesis. Circumference size in top predator absence diagrams represents the density decrease, increase or persistence compared to the top predator presence diagram. Arrows represent trophic interactions. Thicker arrows = magnified trophic interactions due to apex consumer extirpation; grey arrows = lost trophic interactions after apex consumer extirpation.
Fig 2.
Diagram of the experimental enclosure.
Diagram of the experimental enclosure and one of the four identical trays that contained stones for macroinvertebrate colonisation and glass tiles for periphyton colonisation. Dimensions are indicated.
Fig 3.
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).
Table 1.
Macroinvertebrate taxa detected as significant indicators for the three barbel density treatments.
Fig 4.
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).
Fig 5.
Periphyton net primary production measured as the chlorophyll-a on tiles for the three experimental treatments.
Bars represent mean ± SE (mg m-2 d-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).