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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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Related in: MedlinePlus

Experimental design.Two experimental sets (A = detritivores only and B = detritivores with predators) in triplicate, six enclosure/exclosure cages in total. Each replicate set included 5 leaf sacks (black squares), each containing 5 leaf bags individually inoculated with different pure fungus strains (1–5). In each leaf sack only one leaf bag was labelled with 32P (circled number).
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pone-0065186-g001: Experimental design.Two experimental sets (A = detritivores only and B = detritivores with predators) in triplicate, six enclosure/exclosure cages in total. Each replicate set included 5 leaf sacks (black squares), each containing 5 leaf bags individually inoculated with different pure fungus strains (1–5). In each leaf sack only one leaf bag was labelled with 32P (circled number).

Mentions: The experiment was performed in six 1-mm mesh enclosure/exclosure cages (70×150×250 cm) compartmented in 5 sections. Each section was filled with about 1.2 wet-kg of alder leaf detritus, which was collected from the study site, carefully washed to remove animals while preserving microbial colonization, and then weighed with a portable balance (precision ±0.5 g). The 1-mm mesh size of the cages prevented predator and prey escape from and entry to the cages, while allowing water exchange and access only to other species with a body size under 1 mm. Five leaf sacks (30×60×80 cm, 1-cm mesh size), each containing 0.6 wet-kg of alder leaf detritus, mimicking natural heaps of detritus, were added to each cage. They were separated by a fine mesh (1 mm) to prevent animals moving from one leaf sack to the others (Fig. 1), whereas the 1-cm mesh size allowed the invertebrates to move in and out of each sack.


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)

Experimental design.Two experimental sets (A = detritivores only and B = detritivores with predators) in triplicate, six enclosure/exclosure cages in total. Each replicate set included 5 leaf sacks (black squares), each containing 5 leaf bags individually inoculated with different pure fungus strains (1–5). In each leaf sack only one leaf bag was labelled with 32P (circled number).
© Copyright Policy
Related In: Results  -  Collection

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

pone-0065186-g001: Experimental design.Two experimental sets (A = detritivores only and B = detritivores with predators) in triplicate, six enclosure/exclosure cages in total. Each replicate set included 5 leaf sacks (black squares), each containing 5 leaf bags individually inoculated with different pure fungus strains (1–5). In each leaf sack only one leaf bag was labelled with 32P (circled number).
Mentions: The experiment was performed in six 1-mm mesh enclosure/exclosure cages (70×150×250 cm) compartmented in 5 sections. Each section was filled with about 1.2 wet-kg of alder leaf detritus, which was collected from the study site, carefully washed to remove animals while preserving microbial colonization, and then weighed with a portable balance (precision ±0.5 g). The 1-mm mesh size of the cages prevented predator and prey escape from and entry to the cages, while allowing water exchange and access only to other species with a body size under 1 mm. Five leaf sacks (30×60×80 cm, 1-cm mesh size), each containing 0.6 wet-kg of alder leaf detritus, mimicking natural heaps of detritus, were added to each cage. They were separated by a fine mesh (1 mm) to prevent animals moving from one leaf sack to the others (Fig. 1), whereas the 1-cm mesh size allowed the invertebrates to move in and out of each sack.

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