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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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Predator impact on prey traits.Above: number of A. aquaticus and L. peregra specimens per gram of leaf litter (Nc) in leaf bags conditioned with one of five fungal strains, with predators (black bars) and without predators (white bars); below: predator impact on prey density (crosses), movement (•, based on percentage of prey labelled with 32P) and Activity Density (○). Numbers in parentheses on abscissa indicate Activity Density (µCi/g) of leaf bags conditioned with different fungus strains.
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pone-0065186-g002: Predator impact on prey traits.Above: number of A. aquaticus and L. peregra specimens per gram of leaf litter (Nc) in leaf bags conditioned with one of five fungal strains, with predators (black bars) and without predators (white bars); below: predator impact on prey density (crosses), movement (•, based on percentage of prey labelled with 32P) and Activity Density (○). Numbers in parentheses on abscissa indicate Activity Density (µCi/g) of leaf bags conditioned with different fungus strains.

Mentions: Each fungus strain took up the radiophosphorus from the incubation media at a different rate, reflecting its rate of colonisation and development (Fig. 2). The Activity Density (AD) of inoculated leaf bags ranged from 0.176 µCi/g for Mucor mucedo to 0.018 µCi/g for Aspergillus niger. In each leaf sack the non-labelled leaf bags remained completely unlabelled at the end of the experiment. The presence of predators had negligible effects on the mean species abundance of the detritivorous species on the resource patches (paired t-test t<1.2, p value >0.25 for both species, Table 1) with a mean impact of PINc = 0.09±0.08 S.E. for A. aquaticus and 0.19±0.15 S.E. for L. peregra (Fig. 2). In the absence of predators, the leaf bags where fungal colonization was highest (i.e. with the highest fungal AD) were the most heavily colonized by detritivores and were associated with the highest 32P uptake; specifically, the abundance of A. aquaticus in the leaf bags was directly correlated with the AD of fungi (R = 0.97, p value <0.01) and its own AD (R = 0.91, p value <0.01).


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)

Predator impact on prey traits.Above: number of A. aquaticus and L. peregra specimens per gram of leaf litter (Nc) in leaf bags conditioned with one of five fungal strains, with predators (black bars) and without predators (white bars); below: predator impact on prey density (crosses), movement (•, based on percentage of prey labelled with 32P) and Activity Density (○). Numbers in parentheses on abscissa indicate Activity Density (µCi/g) of leaf bags conditioned with different fungus strains.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0065186-g002: Predator impact on prey traits.Above: number of A. aquaticus and L. peregra specimens per gram of leaf litter (Nc) in leaf bags conditioned with one of five fungal strains, with predators (black bars) and without predators (white bars); below: predator impact on prey density (crosses), movement (•, based on percentage of prey labelled with 32P) and Activity Density (○). Numbers in parentheses on abscissa indicate Activity Density (µCi/g) of leaf bags conditioned with different fungus strains.
Mentions: Each fungus strain took up the radiophosphorus from the incubation media at a different rate, reflecting its rate of colonisation and development (Fig. 2). The Activity Density (AD) of inoculated leaf bags ranged from 0.176 µCi/g for Mucor mucedo to 0.018 µCi/g for Aspergillus niger. In each leaf sack the non-labelled leaf bags remained completely unlabelled at the end of the experiment. The presence of predators had negligible effects on the mean species abundance of the detritivorous species on the resource patches (paired t-test t<1.2, p value >0.25 for both species, Table 1) with a mean impact of PINc = 0.09±0.08 S.E. for A. aquaticus and 0.19±0.15 S.E. for L. peregra (Fig. 2). In the absence of predators, the leaf bags where fungal colonization was highest (i.e. with the highest fungal AD) were the most heavily colonized by detritivores and were associated with the highest 32P uptake; specifically, the abundance of A. aquaticus in the leaf bags was directly correlated with the AD of fungi (R = 0.97, p value <0.01) and its own AD (R = 0.91, p value <0.01).

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