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Predators and resources influence phosphorus transfer along an invertebrate food web through changes in prey behaviour.

Calizza E, Rossi L, Costantini ML - PLoS ONE (2013)

Bottom Line: The presence of predators had negligible effects on the number of detritivores in the leaf bags, but it did reduce the proportion of (32)P-labelled detritivores and their P uptake.The most strongly affected species was A. aquaticus, whose vagility, trophic overlap with L. peregra and P uptake were all reduced.The results confirm the importance of bottom-up and top-down forces acting simultaneously to regulate nutrient transfer along food chains in patchy habitats.

View Article: PubMed Central - PubMed

Affiliation: Department of Environmental Biology, 'Sapienza' University of Rome, Rome, Italy.

ABSTRACT
Predators play a fundamental role in prey trophic behaviour, with indirect consequences for species coexistence and ecosystem functioning. Resource quality and availability also influence prey trophic behaviour, with potential effects on predator-prey dynamics. Although many studies have addressed these topics, little attention has been paid to the combined effects of predators and resources on prey species coexistence and nutrient transfer along food chains, especially in detritus-based systems. To determine the influence of predators and resource quality on the movement and P uptake of detritivores, we carried out a field experiment on the River Kelvin (Scotland) using (32)P to test the hypothesis of reduced prey vagility among resource patches as a strategy to avoid predation. Thirty leaf sacks containing alder leaves and two detritivore prey populations (Asellus aquaticus and Lymnaea peregra) were placed in cages, half of them with two predator species (Dendrocoelum lacteum and Erpobdella octoculata) and the other half without predators. Five alder leaf bags, each individually inoculated with a different fungus strain to simulate a patchy habitat, were placed inside each leaf sack. One bag in each sack was labelled with (32)P, in order to assess the proportion of detritivores using it as food and thus their movement among the five resource patches. Three replicates for each labelled fungus and each predation treatment (i.e. with and without predators) were left on the riverbed for 7 days. The presence of predators had negligible effects on the number of detritivores in the leaf bags, but it did reduce the proportion of (32)P-labelled detritivores and their P uptake. The most strongly affected species was A. aquaticus, whose vagility, trophic overlap with L. peregra and P uptake were all reduced. The results confirm the importance of bottom-up and top-down forces acting simultaneously to regulate nutrient transfer along food chains in patchy habitats.

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AD of fungi and TTI of detritivores.Relationship between fungal AD (µCi/g) and Trophic Transfer Index of Asellus aquaticus and Lymnaea peregra in presence (P) and absence (NP) of predators. Note that for A. aquaticus in absence of predators TTI values are reported on right axis.
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pone-0065186-g005: AD of fungi and TTI of detritivores.Relationship between fungal AD (µCi/g) and Trophic Transfer Index of Asellus aquaticus and Lymnaea peregra in presence (P) and absence (NP) of predators. Note that for A. aquaticus in absence of predators TTI values are reported on right axis.

Mentions: In the presence of predators, the consumption of the five resource patches by A. aquaticus was more homogeneous than in the absence of predators (Fig. 3); together with the declining P uptake, this altered the quantity and pattern of phosphorus transfer through the system (Fig. 4). The presence of predators lowered the mean Trophic Transfer index (TTI) of A. aquaticus (paired t-test t = 4.1, p value = 0.01; Table 1 and Fig. 5) from 360.6±97 to 75.4±29 (80±4% reduction), whereas no effect of predation on the TTI of L. peregra was observed. The TTI of both species was negatively correlated with the AD of fungi, in both the presence and absence of predators (p value always <0.05, Fig. 5).


Predators and resources influence phosphorus transfer along an invertebrate food web through changes in prey behaviour.

Calizza E, Rossi L, Costantini ML - PLoS ONE (2013)

AD of fungi and TTI of detritivores.Relationship between fungal AD (µCi/g) and Trophic Transfer Index of Asellus aquaticus and Lymnaea peregra in presence (P) and absence (NP) of predators. Note that for A. aquaticus in absence of predators TTI values are reported on right axis.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3672138&req=5

pone-0065186-g005: AD of fungi and TTI of detritivores.Relationship between fungal AD (µCi/g) and Trophic Transfer Index of Asellus aquaticus and Lymnaea peregra in presence (P) and absence (NP) of predators. Note that for A. aquaticus in absence of predators TTI values are reported on right axis.
Mentions: In the presence of predators, the consumption of the five resource patches by A. aquaticus was more homogeneous than in the absence of predators (Fig. 3); together with the declining P uptake, this altered the quantity and pattern of phosphorus transfer through the system (Fig. 4). The presence of predators lowered the mean Trophic Transfer index (TTI) of A. aquaticus (paired t-test t = 4.1, p value = 0.01; Table 1 and Fig. 5) from 360.6±97 to 75.4±29 (80±4% reduction), whereas no effect of predation on the TTI of L. peregra was observed. The TTI of both species was negatively correlated with the AD of fungi, in both the presence and absence of predators (p value always <0.05, Fig. 5).

Bottom Line: The presence of predators had negligible effects on the number of detritivores in the leaf bags, but it did reduce the proportion of (32)P-labelled detritivores and their P uptake.The most strongly affected species was A. aquaticus, whose vagility, trophic overlap with L. peregra and P uptake were all reduced.The results confirm the importance of bottom-up and top-down forces acting simultaneously to regulate nutrient transfer along food chains in patchy habitats.

View Article: PubMed Central - PubMed

Affiliation: Department of Environmental Biology, 'Sapienza' University of Rome, Rome, Italy.

ABSTRACT
Predators play a fundamental role in prey trophic behaviour, with indirect consequences for species coexistence and ecosystem functioning. Resource quality and availability also influence prey trophic behaviour, with potential effects on predator-prey dynamics. Although many studies have addressed these topics, little attention has been paid to the combined effects of predators and resources on prey species coexistence and nutrient transfer along food chains, especially in detritus-based systems. To determine the influence of predators and resource quality on the movement and P uptake of detritivores, we carried out a field experiment on the River Kelvin (Scotland) using (32)P to test the hypothesis of reduced prey vagility among resource patches as a strategy to avoid predation. Thirty leaf sacks containing alder leaves and two detritivore prey populations (Asellus aquaticus and Lymnaea peregra) were placed in cages, half of them with two predator species (Dendrocoelum lacteum and Erpobdella octoculata) and the other half without predators. Five alder leaf bags, each individually inoculated with a different fungus strain to simulate a patchy habitat, were placed inside each leaf sack. One bag in each sack was labelled with (32)P, in order to assess the proportion of detritivores using it as food and thus their movement among the five resource patches. Three replicates for each labelled fungus and each predation treatment (i.e. with and without predators) were left on the riverbed for 7 days. The presence of predators had negligible effects on the number of detritivores in the leaf bags, but it did reduce the proportion of (32)P-labelled detritivores and their P uptake. The most strongly affected species was A. aquaticus, whose vagility, trophic overlap with L. peregra and P uptake were all reduced. The results confirm the importance of bottom-up and top-down forces acting simultaneously to regulate nutrient transfer along food chains in patchy habitats.

Show MeSH
Related in: MedlinePlus