DOI: 10.5061/dryad.s8n05
title: Data from: Balancing food and density-dependence in the spatial distribution of an interference-prone forager

description: Foraging distributions are thought to be density-dependent, because
 animals not only select for a high availability and quality of resources,
 but also avoid conspecific interference. Since these processes are
 confounded, their relative importance in shaping foraging distributions
 remains poorly understood. Here we aimed to rank the contribution of
 density-dependent and density-independent effects on the spatio-temporal
 foraging patterns of eurasian oystercatchers. In our intertidal study
 area, tides caused continuous variation in oystercatcher density,
 providing an opportunity to disentangle conspecific interference and
 density-independent interactions with the food landscape. Spatial
 distributions were quantified using high-resolution individual tracking of
 foraging activity and location. In a model environment that included a
 realistic reconstruction of both the tides and the benthic food, we tested
 a family of behaviour-based optimality models against these tracking data.
 Density-independent interactions affected spatial distributions much more
 strongly than conspecific interference, even in an interference-prone
 species like oystercatchers. Spatial distributions were governed by
 avoidance of bill injury costs, selection for high interference-free
 intake rates and a decreasing availability of benthic bivalve prey after
 their exposure. These density-independent interactions outweighed
 interference competition in terms of effect size. We suggest that the
 bottleneck in our mechanistic understanding of foraging distributions may
 be primarily the role of density-independent prey attributes unrelated to
 intake rates, like damage costs in the case of oystercatchers foraging on
 perilous prey. At a landscape scale, above the finest inter-individual
 distances, effects of conspecific interaction on spatial distributions may
 have been overemphasised.
description: benthic survey of
 Cockles and American Razor clamsBenthic survey of
 Cockles (Cerastoderma edule) and American razor clams (Ensis directus) in
 the Balgzand area, Wadden Sea, The Netherlands. Aimed at assessing the
 available food stock for Oystercatchers at a high spatial resolution.
 Contains over 3000 sampling points on 15 sampling grids of 50 meter
 resolution. Survey was performed autumn 2011, and repeated in spring
 2012.benthos.zipC code to calculate ideal free distribution for a generalised functional responseThis is a library written in the C programming language, for solving the ideal-free distribution for a generalised functional response with exponential interference function. This library can be called from R, to speed up model fits using Bayesian MCMC methods.IFD-R.cDGPS measurements of bathymetric heightDGPS measurements on Balgzand intertidal area, on 20 May 2012. These measurements were performed to verify the accuracy of the bathymetric maps, and to determine the height at which pressure loggers to measure tidal height were deployed in the Balgzand study area.dgps.txtGPS tracking and accelerometer data of individual Eurasian Oystercatchers foraging in the intertidalThis file contains GPS tracking data and accelerometer data of 10 individually tracked Eurasian Oystercatchers. GPS fixes have been linked to metadata on weather, sun/moon position, bathymetry and tidal information. Covers the period 1 August 2011 - 1 Mar 2012.GPS.txt.zipKriging interpolation estimates of intertidal bivalve densities and biomassKriging interpolation estimates for Cockle and Razor clam densities, lengths, and fresh weights, based on benthic survey data of the intertidal food stock of Eurasian Oystercatcherskrige.ziptidal height measurements based on diving pressure logger datapressure logger data for four locations in the Balgzand intertidal area, used to measure the local water height in the study areapressureloggers.zipR code to fit Oystercatcher distribution models, using MCMC samplingContains R code to fit all spatial distribution models for Oystercatchers based on generalised functional responses, using MCMC sampling. Also contains all required benthos, bathymetric and GPS data in the form of R data frames to run the models.R_code_data.zipbathymetric map of Balgzand intertidal area in the Dutch Wadden SeaBased on the cycle 5 bathymetric map for the Dutch Wadden Sea at 20 meter resolution, prepared by Rijkswaterstaat, Ministry of Infrastructure and the Environment, the Netherlands, with a few improvements and patches.Balgzand2009_patch0308_DGPSCorrected.asc.zip