DOI: 10.5061/dryad.3124p62
title: Data from: Nonlinear effects of intraspecific competition alter landscape-wide scaling up of ecosystem function

description: A major focus of ecology is to understand and predict ecosystem function
 across scales. Many ecosystem functions are only measured at local scales,
 while their effects occur at a landscape level. Here, we investigate how
 landscape-scale predictions of ecosystem function depend on intraspecific
 competition, a fine-scale process, by manipulating intraspecific density
 of shredding macroinvertebrates and examining effects on leaf litter
 decomposition, a key function in freshwater ecosystems. For two species,
 we found that per-capita leaf processing rates declined with increasing
 density following power functions with negative exponents, likely due to
 interference competition. To demonstrate consequences of this
 nonlinearity, we scaled up estimates of leaf litter processing from
 shredder abundance surveys in 10 replicated headwater streams. In
 accordance with Jensen’s inequality, applying density-dependent
 consumption rates reduced estimates of catchment-scale leaf consumption by
 an order of magnitude relative to density-independent rates.
 Density-dependent consumption estimates aligned closely with metabolic
 requirements in catchments with large, but not small, shredder
 populations. Importantly, shredder abundance was not limited by leaf
 litter availability and catchment-level leaf litter supply was much higher
 than estimated consumption. Thus leaf litter processing was not limited by
 resource supply. Our work highlights the need for scaling-up which
 accounts for intraspecific interactions.
description: Experimental and field
 survey data for amphipods and leaf litterCODE: The analysis for
 this manuscript can be performed using the R code contained in the R
 markdown file DEF_code_Little_et_al.Rmd. GIS FILES: There are 11
 shapefiles in this folder which are used in the R code. EXPERIMENTAL AND
 FIELD DATA: There are eight CSV files of data which are described below.
 Variable names and metadata are described in the README.
 GF_densitytreatments_weights.csv: This file contains weights of Gammarus
 fossarum amphipods used in the experiments, in milligrams. Each row
 represents an individual amphipod. DV_densitytreatments_weights.csv: This
 file contains weights of Dikerogammarus villosus amphipods used in the
 experiments, in milligrams. Each row represents an individual amphipod.
 GF_weight_and_survival_data_corrected.csv: This file contains information
 on the survival of G. fossarum amphipods in the density experiment, as
 well as the mass loss of the leaves used in the experiment. Each row
 represents one experimental unit (mesocosm) used in the experiment.
 DV_weight_and_survival_data.csv: This file contains information on the
 survival of D. villosus amphipods in the density experiment, as well as
 the mass loss of the leaves used in the experiment. Each row represents
 one experimental unit (mesocosm) used in the experiment.
 Combined_Data_amphipods.csv: This file contains the amphipod abundance
 information from the April 2015 field surveys (also described in Little
 & Altermatt 2018 Proceedings B). Each row represents one sampling
 point. Combined_Data_leaves.csv: This file contains the benthic leaf
 litter and amphipod abundance information from four sampling bouts: April
 2015, July 2015, November 2015, and January 2016 (also described in Little
 & Altermatt 2018 Proceedings B and Little & Altermatt 2018
 Landscape Ecology). Each row represents one sampling point at one sampling
 bout. leaf_litter_trap_cumulative.csv: This file contains the data from
 leaf litter traps deployed between September and December, 2015, near Lake
 Constance (also presented in Little & Altermatt 2018 Landscape
 Ecology). Traps were first deployed on September 8, 2015, for all sites.
 Each row represents a sampling interval at a specific site; the traps were
 emptied and redeployed at each site several times over the course of the
 autumn, so each site has several rows of data. Rows contain information
 about the total amount of plant material accrued in the traps between the
 start of sampling and the end of a given sampling interval, that is, a
 cumulative total during the leaf drop period. Land_use_in_buffers.csv:
 This file contains data about the area (square meters) of three types of
 land cover in a 1-meter buffer on either side of the stream channels in
 each catchment. Land cover in the buffer zones was calculated from
 Swisstopo GIS layers in ArcMap as described in the methods section of the
 manuscript.DRYAD_Little_et_al_DEF.zip