DOI: 10.5061/dryad.905qfttzs
title: Predator size structure fails to alter nonconsumptive effects in streams

description: Predator population size structure varies over space and time, mediating
 the top-down, consumptive effects of predators on ecosystems. Yet the role
 of predator size variation in governing nonconsumptive predator effects
 has received little targeted research attention. We manipulated stonefly
 (Acroneuria abnormis) predator size structure and feeding ability and
 measured effects on the benthic invertebrate prey community in a headwater
 stream. Field enclosures retained stonefly predators but allowed smaller
 prey to emigrate as a behavioral avoidance response. Stoneflies caused a
 ~30% reduction in total prey abundance regardless of whether or not they
 could feed, indicating a major role for nonconsumptive effects in
 determining the overall predator effect. This pattern was consistent
 across two different stonefly predator size structures with equivalent
 total biomass, as well as most prey responses measured at both the
 community level and the individual taxon level. Our study demonstrates
 that stonefly predators cause a community-scale nonconsumptive effect and
 suggests that predator biomass, rather than predator size structure, might
 determine the strength of this effect.
description: # Predator size structure fails to alter nonconsumptive effects in streams
 Dataset DOI:
 [10.5061/dryad.905qfttzs](https://doi.org/10.5061/dryad.905qfttzs) ##
 Description of the data and file structure We ran an experiment testing
 the effects of stonefly predator size structure (small vs. large) and
 mouthpart gluing (unglued vs. glued) on prey community structure in
 streams. Our experiment crossed these factors resulting in 4 unique
 treatments and we additionally conducted a no-stonefly control. We
 considered effects of experimental factors on aspects of prey community
 structure (measured through abundance data) as well as prey size structure
 (measured using prey head width data).  ### Files and variables #### File:
 Enclosure_experiment_data_10-15-25.csv **Description:** Data are in a CSV
 format and are viewable in MS Excel. Each row in this data set represents
 a single prey individual that was sampled from an experimental
 enclosure. Some prey head width data are missing due to damaged samples
 and, therefore, encoded as NA. ##### Variables * block: The temporal block
 * start: The day the block began * end: The day the block ended *
 start_temp: The stream temperature at the start of block (degrees Celsius)
 * end_temp: The stream temperature at the end of block (degrees Celsius) *
 start_flow: The current velocity at the start of block (feet per second) *
 end_flow: The current velocity at the end of block (feet per second) *
 enclosure: A numerical code for the particular enclosure used * unit: The
 number of the experimental unit * replicate: The replicate number of each
 treatment * individual: The individual insect prey number * general_taxon:
 The general taxon of prey (e.g., Order) * taxon: The more specific taxon
 of prey (e.g., a genus) * conversion_rate: Conversion used to measure prey
 head capsule width under the microscope * width_marks: The number of width
 marks on the microscope scale bar * head_width: Individual prey head
 capsule width in mm * size: Stonefly size treatment * glued_or_unglued:
 Stonefly mouthpart gluing treatment * treatment: Treatment as a 5-level
 factor * predator: Whether the treatment included a stonefly predator or
 not ## Code/software R script (Enclosure_experiment_code_9-26-25.R) was
 written and run using R version 4.3.0. The R script runs all the analyses
 and creates all figures presented in the published article. The package
 versions used in running this script are:  ggplot2 - ‘3.4.2’ dplyr
 - ‘1.1.2’ lme4 - ‘1.1.33’ lmerTest - ‘3.1.3’ multcomp - ‘1.4.24’ emmeans
 - ‘1.8.6’ pbkrtest - ‘0.5.2’ scales - ‘1.2.1’ vegan - ‘2.6.6.1’ DHARMa
 - ‘0.4.6’ reshape2 - ‘1.4.4’ tidyverse - ‘2.0.0’ ggvegan - ‘0.1.999’
 devtools - ‘2.4.5’ cowplot - ‘1.1.3’ Rmisc - ‘1.1.3’ ggsci - ‘3.2.0’