DOI: 10.5061/dryad.bk200
title: Data from: Natural selection by pulsed predation: survival of the thickest

description: Selective predation can lead to natural selection in prey populations and
 may alleviate competition among surviving individuals. The processes of
 selection and competition can have substantial effects on prey population
 dynamics, but are rarely studied simultaneously. Moreover, field studies
 of predator-induced short-term selection pressures on prey populations are
 scarce. Here we report measurements of density dependence in body
 composition in a bivalve prey (edible cockle, Cerastoderma edule) during
 bouts of intense predation by an avian predator (red knot, Calidris
 canutus). We measured densities, patchiness, morphology, and body
 composition (shell and flesh mass) of cockles in a quasi-experimental
 setting, i.e. before and after predation in three similar plots of 1 ha
 each, two of which experienced predation, and one of which remained
 unvisited in the course of the short study period and served as a
 reference. An individual's shell and flesh mass declined with cockle
 density (negative density dependence). Before predation, cockles were
 patchily distributed. After predation, during which densities were reduced
 by 78% (from 232 m-2 to 50 m-2), the patchiness was substantially reduced,
 i.e. the spatial distribution was homogenized. Red knots selected juvenile
 cockles with an average length of 6.9 mm (SD 1.0). Cockles surviving
 predation had heavier shells than before predation (an increase of 21.5
 percentage points), but similar flesh masses. By contrast, in the
 reference plot shell mass did not differ statistically between initial and
 final sampling occasions, while flesh mass was larger (an increase of 13.2
 percentage points). In this field-study, we show that red knots imposed a
 strong selection pressure on cockles to grow fast with thick shells and
 little flesh mass, with selection gradients among the highest reported in
 the literature.
description: data on cockle body
 composition and densityThis file contains the
 field data underlying the analyses of density dependence among cockles
 (figure 1 and Table 1) as well as for calculating relative body
 composition (online figure S2). An explanation of the variables is
 included in the supplementary file
 "1_body_composition_density_dependence_readme.txt".1_body_composition_density_dependence.csvr script for calculating relative body compositionThis is the R script to calculate relative cockle body compositions using the data from file 1: "1_body_composition_density_dependence.csv".1_relative_body_composition.rspatial data on densities of cockles before and after predationThis file contains the data underlying the analyses of spatial density distributions of cockles before and after predation (figure 2), and for calculating autocorrelation functions (figure 3). An explanation of the variables is included in the supplementary file "2_spatial_density_distribution_predation_readme.txt".2_spatial_density_distribution_predation.csvdata on length distributions and body composition before and after predationThis is the data underlying the analyses of length distributions (figure 4) and cockle body composition (figure 5 and online Table S1) before and after predation by red knots, as well as for calculating selection gradients (Table 2). An explanation of the variables is included in the supplementary file "3_body_composition_predation_readme.txt".3_body_composition_predation.csvgeneral documentationRead me first.