DOI: 10.5061/dryad.6q573n68k
title: Predation alters community structure through multiple trophic cascades

description: Predation plays a crucial role in shaping community structure and can
 initiate trophic cascades that alter abundances across adjacent trophic
 levels. Intraspecific variation among predators could lead to varying
 levels of top-down control with implications for trophic cascade strength.
 In this experiment, we manipulated body size variation in populations of
 predatory mole salamanders (Ambystoma talpoideum) within mesocosms and
 monitored a suite of abiotic and biotic responses. Measurements of these
 responses are contained within this dataset. We predicted that
 predator populations with increased body size variation would have limited
 top-down control due to weaker interactions with greater numbers of prey
 species. Conversely, we predicted that populations with similarly sized
 predators would have strong control over fewer prey species, leading to
 trophic cascades. Salamander presence affected nearly every parameter
 measured, suppressing some populations (e.g., invertebrate predators) and
 facilitating others (e.g., invertebrate collectors), triggering multiple
 trophic cascades across several trophic channels, including both “green”
 and “brown” pathways. However, only a few invertebrate taxa responded to
 variation in predator body size, and in nearly all these instances, those
 taxa responded more strongly to treatments with increased body size
 variation than to treatments with similarly sized predators. In contrast
 to our hypothesis, predator size variation may promote individual dietary
 specialization of differently sized predators, resulting in strong control
 of focal prey. These results demonstrate that predators can have pervasive
 and multichannel effects on all trophic levels within communities,
 regardless of size structure, and that increased body size variation can
 lead to stronger top-down control.
description: # Predation alters community structure through multiple trophic cascades
 Dataset DOI: [10.5061/dryad.6q573n68k](10.5061/dryad.6q573n68k) ##
 Description of the data and file structure This study examined how
 predator body size variation shapes aquatic community structure. We
 conducted mesocosm experiments with size-structured predatory mole
 salamanders and collected a suite of abiotic and biotic parameters, which
 are provided here. The primary dataset presents data collected at periodic
 sampling bouts, while the secondary dataset presents tadpole abundance
 data collected at times other than these core sampling bouts. Results of
 the mesocosm experiment revealed dual trophic cascades triggered by mole
 salamanders, highlighting the pervasive, multi-channel influence of
 predators across all trophic levels in pond communities. ### Files and
 variables #### **File: PredationAltersCommunityStructure2024\_Data.csv**
 **Description:** Data collected in each mesocosm during the study period
 of April - September 2016. Mesocosms were constructed in 1000L cattle
 tanks and spatially divided into six blocks with two replicates of each
 treatment (High size variation, Low size variation, or Control) per block
 for a total of 36 mesocosms. Collected data include water quality
 parameters, tadpole abundances, decomposition (ash-free dry mass),
 chlorophyll-*a* concentrations (in periphyton and phytoplankton),
 zooplankton, invertebrate communities (in the benthos and in leaf packs),
 and surface coverage of bladderwort & algae mats. Any columns prefixed
 with ‘LP_’ indicate data collected from leaf packs placed at the beginning
 of the experiment, and any columns prefixed with ‘Benthos’ indicate data
 collected from grab-sampling of the benthic leaf litter. As described in
 the Methods of the associated article, invertebrates were assigned to one
 of four functional feeding groups, and invertebrate taxa biomasses were
 calculated using length-mass regressions. Abundances and biomasses of
 certain specific taxa are detailed at the end of the spreadsheet,
 otherwise, all invertebrate data are reported to the functional feeding
 group level. Leaf packs (invertebrates and ash-free dry mass) and
 periphyton data were not collected in April at the initiation of the
 experiment. Tadpole data was not collected until the end of May and is
 first reported in June in this dataset. One Benthic sample was lost, from
 the May sampling bout in tank 33. Due to user error, no water quality
 parameters were taken in the April sample for tank 21. Due to an equipment
 error, turbidity was not measured in the June sample for tank 34. Any data
 that was not collected, either intentionally or through error, is noted
 with ‘NA’. **Variables** * Tank: The unique identifier for each individual
 mesocosm tank. The identifier is made up of the block number + the
 treatment number. * Block: One of six spatially arranged blocks to
 compensate for environmental variability across the mesocosm array. Each
 block has six mesocosm tanks. * Treatment: A numerical code for the
 SizeClass treatment, which was replicated twice per block. High variation
 = 1, 3; Low variation = 4, 6; Control =2, 5. * SizeClass: Experimental
 manipulation of body size variation in populations of salamanders.
 Treatments include high body size variation ('High'), low body
 size variation ('Low'), or the absence of salamanders
 ('Control'). * Date: The month in which the observations were
 collected. All observations were collected once per indicated month in
 2016 (approximately 1, 5, 8, 13, and 21 weeks post-addition of salamanders
 on April 14, 2016). * Temperature: Temperature in degrees Celsius of the
 mesocosm water, as measured with a multi-sensor sonde (Yellow Springs
 Incorporated, model 6820). * pH: pH of the mesocosm water, as measured
 with a multi-sensor sonde (Yellow Springs Incorporated, model 6820). * DO:
 Dissolved Oxygen concentration in mg/L of the mesocosm water as measured
 with a multi-sensor sonde (Yellow Springs Incorporated, model 6820). *
 Turbidity: Turbidity in Nephelometric Turbidity Units (NTU, higher values
 indicate higher turbidity) of the mesocosm water as measured with a
 multi-sensor sonde (Yellow Springs Incorporated, model 6820). * ORP:
 Oxidation-Reduction Potential in millivolts (mV) of the mesocosm water as
 measured with a multi-sensor sonde (Yellow Springs Incorporated, model
 6820). * Conductivity: Conductivity of the mesocosm water as measured with
 a multi-sensor sonde (Yellow Springs Incorporated, model 6820). * SRP:
 Soluble Reactive Phosphorus concentrations in mg/L in the mesocosm water.
 * Nitrates: Nitrate concentrations in mg/L in the mesocosm water. * AFDM:
 Ash-Free Dry Mass of leaves from the leaf packs. Data are presented in
 grams and are a measure of decomposition. * Periphyton: Concentrations of
 Chlorophyll-a (mg/m3) in algal periphyton collected from stone tiles
 within the mesocosm. * Phytoplankton: Concentrations of Chlorophyll-a (mg
 per cubic meter) in pelagic phytoplankton collected from mesocosm water. *
 ZoopTotal: Total number of zooplankton per 5mL of mesocosm water. *
 Cladocera: Total number of cladoceran zooplankton per 5mL of mesocosm
 water.  * Rotifera: Total number of rotifer zooplankton per 5mL of
 mesocosm water. * Cyclopoid: Total number of cyclopoid copepods per 5mL of
 mesocosm water. * Nauplii: Total number of nauplii per 5mL of mesocososm
 water. * TadpoleAbund: Counts of tadpoles within mesocosms, as visually
 counted in a fixed 30x40cm quadrat. Tadpole observations were aggregated
 to conform to the dates of the main sampling bouts. * LP_GrandTotal: Total
 counts of invertebrates in the leaf packs, including ostracoda (i.e.,
 invertebrate filterers). * LP_TotalNoOstra: Total counts of invertebrates
 in the leaf packs, excluding ostracoda (i.e,. invertebrate filterers). *
 LP_Predator: Counts of invertebrate predators in the leaf packs. *
 LP_Collector: Counts of invertebrate collectors in the leaf packs. *
 LP_Grazer_NoAncyl: Counts of invertebrate grazers, excluding Ancyclidae,
 in the leaf packs. * LP_Grazer_wAncycl: Counts of invertebrate grazers,
 including Ancyclidae, in the leaf packs. * LP_Filterer: Counts of
 invertebrate filterers in the leaf packs. Filterers were 100% represented
 by Ostracoda. * Benth_Total: Total count of invertebrates in the benthic
 samples. * Benth_Predator: Counts of invertebrate predators in the benthic
 samples. * Benth_Collector: Counts of invertebrate collectors in the
 benthic samples. * Benth_Grazer: Counts of invertebrate grazers in the
 benthic samples. * Benth_Filterer: Counts of invertebrate filterers in the
 benthic samples. * LP_Biomass_Total: Total biomass (mg) of invertebrates
 in the leaf packs, including ostracoda. * LP_Biomass_Total_NoOstra: Total
 biomass (mg) of invertebrates in the leaf packs, excluding ostracoda. *
 LP_Biomass_Predator: Biomasses (mg) of invertebrate predators in the leaf
 packs. * LP_Biomass_Collector: Biomasses (mg) of invertebrate collectors
 in the leaf packs. * LP_Biomass_Grazer: Biomasses (mg) of invertebrate
 grazers in the leaf packs. * LP_Biomass_Filterer: Biomasses (mg) of
 invertebrate filterers (100% represented by ostracoda) in the leaf packs.
 * Benth_Biomass_Total: Total biomass (mg) of invertebrates in the benthic
 samples. * Benth_Biomass_Predator: Biomasses (mg) of invertebrate
 predators in the benthic samples. * Benth_Biomass_Collector: Biomasses
 (mg) of invertebrate collectors in the benthic samples. *
 Benth_Biomass_Grazer: Biomasses (mg) of invertebrate grazers in the
 benthic samples. * SurfaceCoverage_Total: Surface coverage (m^2) of
 floating vegetative mats in the mesocosm tanks. * SurfaceCoverage_Utric:
 Surface coverage (m^2) of just the Utricularia (bladderwort) component of
 floating vegetative mats in the mesocosm tanks. * SurfaceCoverage_Alg:
 Surface coverage (m^2) of just the algal component of floating vegetative
 mats in the mesocosm tanks. * LP_Hydrophilidae: Counts of Hydrophilid
 larvae in the leaf packs. * LP_Chiro: Counts of Chironomidae in the leaf
 packs. * LP_Physidae: Counts of Physid snails in the leaf packs. *
 LP_Ancycl: Counts of Ancyclidae in the leaf packs. * Benthos_Hydro: Counts
 of Hydrophilid larvae in the benthic samples. * Benth_Chiro: Counts of
 Chironomidae in the leaf packs. #### **File:
 PredationAltersCommunityStructure2024\_DataTadpoles.csv**
 **Description:** Counts of tadpoles within mesocosms, as visually measured
 in a fixed 30x40cm quadrat ('Count') and extrapolated to
 abundances per cubic meter of water (CountPerM3). If no tadpoles were
 observed, a value of 0 is recorded. **Variables** * SizeClass:
 Experimental manipulation of body size variation in populations of
 salamanders. Treatments include high body size variation
 ('High'), low body size variation ('Low'), or the
 absence of salamanders ('Control'). * Block: One of six
 spatially arranged blocks to compensate for environmental variability
 across the mesocosm array. * Treatment: A numerical code for the Size
 Class, which was replicated twice per block. High = 1, 3; Low = 4, 6;
 Control =2, 5. * Date: The observation date, all observations were
 conducted in 2016.  * Count: Counts of tadpoles within mesocosms, as
 visually counted in a fixed 30x40cm quadrat * CountPerM3: Counts of
 tadpoles extrapolated to a cubic meter of water. ## Code/software Any
 basic spreadsheet viewer will work with this data. The data are saved in
 Comma Separated Values (.csv) format, which is compatible with a wide
 range of software. ## Access information NA