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Linking Predation Risk, Herbivore Physiological Stress and Microbial Decomposition of Plant Litter
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A healthy but depleted herd: Predators decrease prey disease and density.

Laura K Lopez1, Michael H Cortez2, Turner S DeBlieux3

  • 1Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, Michigan, USA.

Ecology
|May 15, 2023
PubMed
Summary
This summary is machine-generated.

Predators can reduce parasite spread in prey populations, but this "healthy herds" effect may not increase prey density. High predation can harm prey populations, even when parasites are suppressed.

Keywords:
consumer-resourcedensity mediated indirect effectshealthy herdshost-parasiteinfection prevalenceparasitoidpathogenpredationpredator spreader

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Area of Science:

  • Ecology
  • Parasitology
  • Aquatic Ecology

Background:

  • The healthy herds hypothesis suggests predators control prey parasites, boosting prey populations.
  • Evidence for predator-driven parasite reduction and subsequent prey density increases is limited and mixed.
  • Experimental systems are needed to disentangle these complex predator-prey-parasite dynamics.

Purpose of the Study:

  • To experimentally test the healthy herds hypothesis in a planktonic predator-prey-parasite system.
  • To investigate how predator density and parasitism affect prey (Daphnia dentifera) infection prevalence and population density.
  • To assess the role of prey genotype susceptibility in predator-prey-parasite interactions.

Main Methods:

  • Experimental manipulation of predator (Chaoborus punctipennis) and parasite (Metschnikowia bicuspidata) densities.
  • Use of nine Daphnia dentifera genotypes with varying susceptibility to predation and parasitism.
  • Monitoring of infection prevalence and prey density under different treatment levels.

Main Results:

  • Predation significantly reduced parasite infection prevalence, eliminating it at high predator densities.
  • Prey density decreased substantially at high predation levels, contradicting the healthy herds hypothesis's prediction of increased prey density.
  • Model analysis indicated that high infection prevalence prevented the conditions necessary for predation to increase prey density.

Conclusions:

  • Predation can reduce parasite prevalence but may not increase prey density, especially when infection levels are high.
  • High predation can impose a significant density cost on prey populations.
  • Complex interactions, including consumer-resource dynamics, influence predator-prey-parasite systems, and predator introduction for parasite control may negatively impact prey populations.