DOI: 10.5061/dryad.3kb72
title: Data from: Density- and trait-mediated effects of a parasite and a predator in a tri-trophic food web

description: 1. Despite growing interest in ecological consequences of parasitism in
 food webs, relatively little is known about effects of parasites on
 long-term population dynamics of non-host species or about whether such
 effects are density- or trait- mediated. 2. We studied a tri-trophic food
 chain comprised of: (i) a bacterial basal resource (Serratia fonticola),
 (ii) an intermediate consumer (Paramecium caudatum), (iii) a top predator
 (Didinium nasutum), and (iv) a parasite of the intermediate consumer
 (Holospora undulata). A fully-factorial experimental manipulation of
 predator and parasite presence/absence was combined with analyses of
 population dynamics, modelling, and analyses of host (Paramecium)
 morphology and behavior. 3. Predation and parasitism each reduced the
 abundance of the intermediate consumer (Paramecium), and parasitism
 indirectly reduced the abundance of the basal resource (Serratia).
 However, in combination, predation and parasitism had non-additive effects
 on the abundance of the intermediate consumer, as well as on that of the
 basal resource. In both cases, the negative effect of parasitism seemed to
 be effaced by predation. 4. Infection of the intermediate consumer reduced
 predator abundance. Modelling and additional experimentation revealed that
 this was most likely due to parasite reduction of intermediate host
 abundance (a density-mediated effect), as opposed to changes in predator
 functional or numerical response. 5. Parasitism altered morphological and
 behavioural traits, by reducing host cell length and increasing the
 swimming speed of cells with moderate parasite loads. Additional tests
 showed no significant difference in Didinium feeding rate on infected and
 uninfected hosts, suggesting that the combination of these modifications
 does not affect host vulnerability to predation. However, estimated rates
 of encounter with Serratia based on these modifications were higher for
 infected Paramecium than for uninfected Paramecium. 6. A mixture of
 density-mediated and trait-mediated indirect effects of parasitism on
 non-host species creates rich and complex possibilities for effects of
 parasites in food webs that should be included in assessments of possible
 impacts of parasite eradication or introduction.
description: Paramecium &
 Didinium AbundanceRaw data from the main
 experiment, pertaining to ciliate abundances over time. Observations were
 input by row. Column titles specify the following: "day" -- day
 of the experiment on which the observation was made; "repID" --
 replicate label of the microcosm; "trtmt" -- treatment label of
 the microcosm; "prey" -- presence (yes) or absence (no) of
 Paramecium in the microcosm; "predator" -- presence (yes) or
 absence (no) of Didinium in the microcosm; "parasite" --
 presence (yes) or absence (no) of Holospora in the microcosm;
 "species" -- the species to which the observation pertains
 ("PARA" -- Paramecium; "DIDI" -- Didinium);
 "vol" -- the volume sampled for the observation;
 "count" -- the number of individual present within the volume
 sampled.p-d-h_raw_data3.csvSerratia AbundanceRaw data from the main experiment, pertaining to Serratia abundance over time. Observations were input by row. Column titles specify the following: "day" -- day of the experiment on which the observation was made; "repID" -- replicate label of the microcosm; "trtmt" -- treatment label of the microcosm; "prey" -- presence (yes) or absence (no) of Paramecium in the microcosm; "predator -- presence (yes) or absence (no) of Didinium in the microcosm; "parasite" -- presence (yes) or absence (no) of Holospora in the microcosm; "species" -- the species to which the observation pertains ("SERRA" -- Serratia); "Platevol" -- volume of sample (in microliters) plated on agar gel for incubation; "Dilution" -- the factor by which the original sample from the microcosm had been diluted before plating; "Colonies" -- the number of colony-forming units counted on the plate.p-d-h.serra3.csvParamecium Morphology & TrajectoryRaw data obtained from video capture and image analysis of swimming Paramecium ("un" -- uninfected; "inf" -- infected by Holospora).MorphTrajExptData.csv