DOI: 10.5061/dryad.4t9f2
title: Data from: Habitat, predators, and hosts regulate disease in Daphnia through direct and indirect pathways

description: Community ecology can link habitat to disease via interactions among
 habitat, focal hosts, other hosts, their parasites, and predators.
 However, complicated food web interactions (i.e., trophic interactions
 among predators, and their impacts on host density and diversity) often
 obscure the important pathways regulating disease. Here, we disentangle
 community drivers in a case study of planktonic disease, using a two-step
 approach. In step one, we tested univariate field patterns linking
 community interactions to two disease metrics. Density of focal hosts
 (Daphnia dentifera) was related to density but not prevalence of fungal
 (Metschnikowia bicuspidata) infections. Both disease metrics appeared to
 be driven by selective predators that cull infected hosts (fish, e.g.
 Lepomis macrochirus), sloppy predators that spread parasites while feeding
 (midges, Chaoborus punctipennis), and spore predators that reduce contact
 between focal hosts and parasites (other zooplankton, especially
 small-bodied Ceriodaphnia sp.). Host diversity also negatively correlated
 with disease, suggesting a dilution effect. However, several of these
 univariate patterns are initially misleading, due to confounding
 ecological links among habitat, predators, host density, and host
 diversity. In step two, path models uncovered and explained these
 misleading patterns, and grounded them in habitat structure (refuge size).
 First, rather than directly reducing infection prevalence, fish predation
 drove disease indirectly through changes in density of midges and
 frequency of small spore predators (which became more frequent in lakes
 with small refuges). Second, small spore predators drove the two disease
 metrics through fundamentally different pathways: They directly reduced
 infection prevalence, but indirectly reduced density of infected hosts by
 lowering density of focal hosts (likely via competition). Third, the
 univariate diversity-disease pattern (signaling a dilution effect) merely
 reflected the confounding direct effects of these small spore predators.
 Diversity per se had no effect on disease, after accounting for the links
 between small spore predators, diversity, and infection prevalence. In
 turn, these small spore predators were regulated by both size-selective
 fish predation and refuge size. Thus, path models not only explain each of
 these surprising results, but also trace their origins back to habitat
 structure.
description: Summary of field data
 collected during Daphnia epidemicsAll data are seasonal
 averages (September - November). Lakes were sampled weekly or biweekly
 (every other week) during this period. Key to columns: "Lake" =
 lake sampled; "Refuge" = depth of the hypolimnetic refuge
 (meters); "D.size" = average size of adult female D. dentifera
 (the index of fish predation; mm); "Chaob" = density of
 Chaoborus punctipennis (m-2); "Chaob2" = ln(Chaob);
 "D.dens" = density of Daphnia dentifera (cm-2);
 "C.dens" = density of Ceriodaphnia sp. (cm-2);
 "P.dens" = density of Daphnia pulicaria (cm-2);
 "D.freq" = frequency of Daphnia dentifera; "C.freq" =
 frequency of Ceriodaphnia sp.; "P.freq" = frequency of Daphnia
 pulicaria; "Amb.freq" = frequency of Daphnia ambigua;
 "Par.freq" = frequency of Daphnia parvula; "Dia.freq"
 = frequency of Diaphanosoma sp.; "Bos.freq" = frequency of
 Bosmina sp.; "Sca.freq" = frequency of Scaholeberis sp.;
 "Chy.freq" = frequency of Chydorus sp.; "Alo.freq" =
 frequency of Alona sp.; "O.freq" = frequency of all rare
 cladocerans pooled together; "Simpsons" = inverse Simpsons
 diversity index; "M.prev" = infection prevalence of
 Metschnikowia bicuspidata in Daphnia dentifera; "M.dens" =
 density of Daphnia dentifera infected with Metschnikowia bicuspidata
 (cm-2).daphnia.field.disease.summary.csvR script for univariate analysesThis R script recreate Figures 1-5 and S1 (all univariate analyses).daphnia.field.disease.univar.RR script for path modelsThis R script recreates Figures 6 & 7 (path models).daphnia.field.disease.paths.R