DOI: 10.5061/dryad.kh18932h7
title: Data from: Herbivory can increase plant fitness via reduced interspecific competition – evidence from models and mesocosms

description: Herbivores are generally considered to reduce plant fitness. However, as
 in natural communities herbivores often feed on several competing plant
 species, herbivores can also increase plant fitness by reducing
 interspecific competition among plants. In this study, we developed a
 testable model to predict plant fitness in the presence of an
 interspecific competitor and an herbivore that feeds on both plant
 species. Our model allows us to predict at which herbivore and competitor
 densities the focal species will benefit from herbivory. This can be
 estimated by quantifying the effects of the herbivore on the fitness of
 the focal plant and on its competitor, and by estimating the levels of
 intra- and interspecific competition in a pair-wise fashion, respectively.
 We subsequently validated the model in indoor microcosms using three
 interacting species: an aquatic macrophyte (the giant
 duckweed Spirodela polyrhiza), its native competitors (green
 algae), and its native herbivore (the pond snail Lymnaea stagnalis).
 Additional outdoor mesocosm experiments supported our model under natural
 conditions. Together, this study provides a conceptual framework to
 understand how herbivores shape plant fitness in a community context.
description: Files: 1_Exp2c_2d_algae_duckweed__duckweed_algae_day7.csv and
 2_Exp3a,3b_snail_on_algae__snail_on_duckweed_24h_LB.csv
 We tested within laboratory three-species microcosms under which
 starting conditions Spirodela polyrhiza benefitted from the presence of a
 snail herbivore when competing with Chlamydomonas reinhardii. We included
 a treatment with a high number of duckweeds competing against a low
 concentration of algae, and vice versa, as well as two treatments with
 intermediate densities. We grew these combinations in the with either no
 snails, one snail, or two snails. We excluded replicates in which the
 populations collapsed, or snails died within 14 days from the analysis,
 resulting in a data set of n = 3-8 per treatment. The details can be found
 in the Supporting Information (SI Text S2). On day 14 of the experiment,
 we counted the number of live fronds, measured the OD of algae, and
 calculated the per capita growth of both competing species. Data were
 analysed using Wilcoxon tests to compare per capita growth between the
 herbivory and control treatments.
 ProcB_SuppInfo_R_Modelling_v3_LB.Rmd is an R-markdown file that
 describes data analysis processes.
description: # Herbivory can increase plant fitness via reduced interspecific
 competition – evidence from models and mesocosms
 [https://doi.org/10.5061/dryad.kh18932h7](https://doi.org/10.5061/dryad.kh18932h7) ## Description of the data and file structure The folder contains three raw data file (in .csv formate) and three R-markdown file and one R-script for plotting the estimated parameters.  ### Files and variables In all files, NA refers to not available. #### **1\_Exp2c\_2d\_algae\_duckweed\_\_duckweed\_algae\_day7.csv** Experimental data 2-species-mesocosm to learn how the competing species affect each others growth rates: * Column experiment: internal numbering identifying the experiment * Column nr_snails: number of individuals of snails (*Lymneae stagnalis*) * Column rep: labelling of replicate (letter) and treatment (number of starting fronds of *Spirodela polyrhiza*) * Column focal_species: Sp=*Spirodela polyrhiza*, Ch=*Chlamydomonas reinhardii* * Column treatment: with *Chlamydomonas reinhardii* algae, without *Chlamydomonas reinhardii* algae * Column day0: for focal species *Spirodela polyrhiza* it gives the starting number of fronds at the beginning of the experiment, for focal species Chlaydomonas reinhardii it gives the OD of the algae * Column competitor_constant: gives the number of fronds [or the OD of algae culture] which was kept constant over the course of the experiment by active manipulation * Column day7: for focal species *Spirodela polyrhiza* it gives the starting number of fronds at the end of the experiment, for focal species *Chlaydomonas reinhardii* it gives the OD of the algae, NA=not available e. g. because control treatment * Column growth: per capita growth rate per day. #### **2\_Exp3a,3b\_snail\_on\_algae\_\_snail\_on\_duckweed\_24h\_LB.csv** Experimental data of 2-species mesocosm to learn about the consumption of the competition species by snails: * Column experiment: internal numbering identifying the experiment * Column rep: repetition and treatment info  * Column nr_snails: number of individuals of snails (*Lymneae stagnalis*) * Column focal_species: Sp=*Spirodela polyrhiza*, Ch=*Chlamydomonas reinhardii* * Column treatment: herb=herbivory, ctr=control meaning no herbivory * Column hour0: Number of fronds [algae OD] at the start of the experiment * Column hour24: Number of fronds [algae OD] at the end of the experiment * Column consumption_rate: consumption rate of fronds [algae OD], per snail per day * Column consumption_absolute: absolute consumption of fronds [algae OD], per snail per day #### **3\_Exp4\_snail\_algae\_duckweed\_high\_low\_day14.csv** Experimental data 3-species-mesocosm to test szenarios with varying starting parameter: * Column experiment: internal numbering identifying the experiment * Column rep: internal labelling of sample * Column Nr_snails: number of individuals of snails (*Lymneae stagnalis*) * Column focal_species: all meaning both competing species (*Spirodela* and *Chlamydomonas*) * Column treatment: combinations of varying starting conditions meaning Sp=*Spirodela polyrhiza*, Ch=*Chlamydomonas reinhardii*, Medium,High,Low=refer to different amounts of starting densities of the competing species * Column treatment2: herbivory=presence of snail, control=absence of snail * Column Sp_day0: Sp=Spirodela, day0= starting day of the experiment... giving the number of starting Spirodela fronds at the beginning of the experiment * Column Sp_day14: Sp=*Spirodela*, day14=end day of the experiment. The number of Spirodela fronds present at the end of the experiment is shown * Column Ch_day0: analogous to Column Sp_day0 but here giving the OD of *Chlamydomonas* algae * Column Ch_day14: analogous to Column Sp_day14 but here giving the OD of *Chlamydomonas* algae * Column Sp_growthrate: giving the growth rate of *Spirodela polyrhiza* (Sp), per capital per day * Column Ch_growthrate: giving the growth rate of *Chlamydomonas reinhardii* (Ch), per capital (cell) per day ## Code/software FILE **RScript "analysis_algae - LB_sep.Rmd"** R Script corresponding to metabarcoding analysis of samples collected in outdoor mesocosms for duckweed samples with attached microalgae (18S) and (cyano-)bacteria (16S) \- R packages are listed within the Script FILE **RScript "analysis_macroalgae - LB_sep.Rmd"** R Script corresponding to metabarcoding analysis of samples collected in outdoor mesocosms for macroalgae samples (18S) \- R packages are listed within the Script FILE **RScript "ProcB_SuppInfo_R_Modelling_v4_LB.Rmd"** R Script corresponding to modelling approach to extract the model coefficients. Model was fed with data from excel files described above. FILE **RScript "BarplotsCoefficients_Bootstrap_sep.R"** R Script to generate the barplots of the coefficients obtained from the modelling approach  ## Access information Other publicly accessible locations of the data: * Raw sequencing data is available on NCBI SRA under BioProject PRJNA914505 (16S duckweed samples), PRJNA914509 (18S duckweeds samples), PRJNA996071 (18S algae samples). Data was derived from the following sources: * NA