DOI: 10.5061/dryad.9kd51c5pv
title: Explaining variation in plant-herbivore associational effects in a tree biodiversity experiment

description: Within biodiversity-ecosystem function research, a major outstanding
 question is how herbivory, a critical ecosystem function at the base of
 the food web, changes along gradients of plant
 biodiversity. Neighborhood-level associational effects are
 hypothesized to be a strong driver of biodiversity-herbivory
 relationships, but we lack a successful framework that explains the wide
 variation observed in the sign and magnitude of plant-herbivore
 associational effects, particularly in systems with mainly generalist
 herbivores. In this study, we combine measurements from a tree
 biodiversity field experiment with simulation to provide a framework for
 explaining variation in plant-herbivore associational effects,
 particularly when herbivores that feed on many different species (e.g.,
 generalists) cause most damage. We show that monoculture herbivory levels
 of focal species and their neighbors predict the direction and strength of
 associational effects. We provide evidence that this may be due to a
 “spillover effect”, in which some insect herbivores attracted to focal
 individuals ultimately end up feeding on neighboring individuals. With an
 empirically parameterized simulation, we explain how spatial organization
 modifies biodiversity-ecosystem function relationships when associational
 effects operate. We suggest a set of experiments to test the generality of
 our conceptual framework, to elucidate the underlying mechanisms that
 produce the patterns we find, and to ultimately increase the
 predictability of plant-herbivore associational effects. We conclude by
 discussing how our results might inform pest management in diversified
 agroecosystems and reforestation sites. Synthesis Our results provide a
 potential framework for explaining why positive and negative
 plant-herbivore associational effects are often balanced in systems with
 primarily generalist herbivores and point to a path forward for predicting
 when increased plant biodiversity will be associated with increased,
 decreased, or unchanged levels of insect herbivory on individual plant
 species in such systems.  
description: We include here six datasets. Three (mini_mydiv_herbivory.csv,
 mydiv_herbivory_may_2021.csv, and mydiv_herbivory_aug_2021.csv) contain
 leaf-level herbivory data. Columns in this data show the block, plot,
 diversity of the plot (1, 2, or 4), mycorrhizal characteristics of the
 plot (A for only arbuscular mycorrhizae, E for only ectomycorrhizae, and
 AE for both types), tree species, position of the individual within the
 plot, and branch on the individual. Additional columns show
 presence/absence of herbivory on each leaf due to leaf chewers,
 holefeeders, leafminers, gallers, leafrollers, and skeletonizers, as well
 as the presence of infection (rust or mildew). Additionally, in the August
 2021 dataset, an additional column gives a quantitative herbivory index
 for each leaf, and the "perc_mean" column gives the midpoint of
 the % leaf area removed category to which that index corresponds
 to.  sem_14.csv and sem_nopalat.csv contain leaf trait
 data collected in July and August 2021, averaged at the level of the tree
 individual (i.e., as the data was used in SEM's described in the
 manuscript). They show for each tree individual, the plot in which it was
 located, the species, the position within the plot, the pubescence on a 1
 cm diameter disc on each side of the leaf and the sum of these two
 measurements, the average toughness across multiple leaves. Additionally,
 sem_14.csv contains data on leaf palatability derived from feeding trials
 with caterpillars. Since palatability trials were only conducted for
 leaves from diversity levels 1 and 4, this dataset only contains data from
 those diversity levels. sem_nopalat.csv omits palatability data, but
 contains data on the other traits for all three diversity
 levels. Finally, tree_inventory_2021.csv contains dbh
 and height data (along with plot, position, and species identifiers) for
 trees across the MyDiv experiment in 2021.  Additional
 methods on data collection can be found in the manuscript main text and
 supporting information. 
description: # Data for the publication "Explaining variation in plant-herbivore
 associational effects in a tree biodiversity experiment" These
 datasets may be accessed on Dryad at
 https://doi.org/10.5061/dryad.9kd51c5pv These datasets were collected in
 2016 and 2021, and used in the manuscript “Explaining variation in
 plant-herbivore associational effects in a tree biodiversity experiment”.
 The datasets contain information on insect herbivory, leaf traits, and
 plant size. Methods for data collection can be found in the manuscript and
 supporting information. The datasets
 "mydiv\_herbivory\_may\_2021.csv" contains the data on herbivory
 in May, 2021 due to different functional groups. The columns contain the
 following information: * "Plot": the plot number, the
 mycorrhizal treatment (E for ecto, A for arbuscular, and AE for mixed),
 and the diversity level * "tree.species": the binomial
 nomenclature for each tree species * "Indiv": the tree
 individual of a given species within the plot -- either 1, 2, or 3, as
 there were three replicate tree individuals per species per plot *
 "Position": the position within the 12x12 grid of each plot,
 with the letter giving one coordinate and the number the other *
 "Leaf": The leaf on the tree individual; there are 15 leaves per
 individual * "Chewer", "Holefeeder",
 "Miner", "Galler", "Roller",
 "Sucking", "Skeletonizer", "Rust",
 "Mildew", "Dasineura-like galls": In each of these
 columns, we denote the presence (1) or absence (0) of a different kind of
 leaf damage: leaf chewer, holefeeders, leaf miners, gallers, leaf rollers,
 leaf suckers, skeletonizers, rust, mildew, or dasinuera-like galls.
 Further descriptions of different types of herbivore damage are provided
 in the manuscript. * "plot\_sp\_position": simply the plot,
 tree.species, and position columns pasted together, giving a unique ID for
 each tree individual The dataset
 "mydiv\_herbivory\_aug\_2021.csv" contains the data on herbivory
 in August, 2021, both due to different functional groups and a
 quantitative metric per leaf. The columns contain the following
 information: * "plot": the plot number * "species":
 the binomial nomenclature for each tree species * "branch": the
 branch of the tree on which leaves were sampled; leaves were sampled on
 three branches per tree * "position": the position within the
 12x12 grid of each plot, with the letter giving one coordinate and the
 number the other * "Leaf": The leaf on the tree individual;
 there are 15 leaves per individual * "chewer",
 "holefeeder", "miner", "galls",
 "roller", "skeletonizer", "rust",
 "mildew": In each of these columns, we denote the presence (1)
 or absence (0) of a different kind of leaf damage: leaf chewer,
 holefeeders, leaf miners, gallers, leaf rollers, skeletonizers, rust, or
 mildewFurther descriptions of different types of herbivore damage are
 provided in the manuscript. * "index": the quantitative
 herbivory index for each leaf (descriptions of categories are provided in
 the manuscript) * "my": the mycorrhizal type of the plot *
 "div": the diversity level of the plot * "perc\_mean":
 the median of the range of herbivory values corresponding to the index *
 "block": the block of the experiment The dataset
 "mini\_mydiv\_herbivory.csv" contains the data on herbivory in
 the miniMyDiv experiment in September, 2016. The columns contain the
 following information: * "Plot": the plot number/name, the
 diversity level, and the mycorrhizal treatment * "species": the
 binomial nomenclature for each species * "Indiv": the tree
 individual for a given species within the plot * "Leaf": the
 leaf per individual * "Chewer", "Holefeeder",
 "Miner", "Galler", "Roller",
 "Sucking", "Skeletonizer", "Rust",
 "Mildew" The dataset "sem\_14.csv" contains the data
 on leaf traits sampled in July and August, 2021. Only data from diversity
 levels 1 and 4 are included, as palatability data was only collected at
 this level. The columns contain the following information: *
 "Plot": the plot number * "species": The binomial
 nomenclature for each species * "position": the position of the
 tree within the plot * "pubesc.sum": a pubescence index for each
 leaf, calculated by summing the pubescence on the abaxial and adaxial
 sides * "toughness.avg": the average leaf toughness measurement
 across leaves for a given tree * "palat\_ind": the average
 palatability index across leaves within a tree The dataset
 "sem\_nopalat.csv" contains the data on leaf traits sampled in
 July and August, 2021, but without palatability data. However, it contains
 leaf trait data for all diversity levels. The columns contain the
 following information: * "id": the plot number, species, and
 position within the plot * "pubesc.sum": a pubescence index for
 each leaf, calculated by summing the pubescence on the abaxial and adaxial
 sides * "toughness.avg": the average leaf toughness measurement
 across leaves for a given tree * "species": the binomial
 nomenclature for each species * "plot": the plot number *
 "position": the tree individual position within the plot The
 dataset "tree\_inventory\_2021.csv" contains the data on tree
 size from 2021. The columns contain the following information: *
 "plot": the plot number * "position": the tree
 individual position within the plot * "species": the binomial
 nomenclature for each tree species * "dbh": diameter at breast
 height of each individual * "height": tree height *
 "id": a unique id for each tree individual, made up of the plot
 number, species, and position pasted together