DOI: 10.5061/dryad.c866t1gf7
title: Quantifying direct and indirect effects of early-season herbivory on reproduction across four brassicaceous plant species

description: Insect herbivores can directly affect plant reproduction by feeding on
 reproductive tissues, or indirectly by feeding on vegetative tissues for
 which plants are unable to compensate. Additionally, early-arriving
 herbivores may have cascading effects on plant reproduction by altering
 the later-arriving community. However, the dynamic interplay between plant
 development and the assembly of herbivore communities remains
 underexplored. Hence, it is unclear whether non-outbreak levels of ambient
 herbivory early in the development of plants can impact plant fitness and
 to what extent these effects are mediated through changes in plant
 development and subsequent herbivory. By excluding the herbivore community
 in an exclosure experiment and by manipulating early-season herbivory in a
 common garden field experiment replicated across four Brassicaceae species
 and two years, we tested whether early-season herbivory by caterpillars
 (Pieris rapae) or aphids (Myzus persicae) affected development,
 reproduction, and the herbivore communities associated with individual
 plants. In addition, we tested a causal hypothesis to assess the relative
 importance and temporal interplay between variation in herbivore
 communities and variation in plant development in determining plant
 reproduction. Early-season herbivory affected plant reproduction
 in the exclosure experiment, with effects being highly dependent on the
 plant species, the herbivore species, and the year. However, we found no
 such effects in the field experiment. The exploratory path analysis
 indicated that variation in plant reproduction is best predicted by
 variation in plant development, explaining 80% of the total effect on seed
 production. This suggests that early-season herbivory had limited effects
 on later plant development, and plants were able to attenuate the impact
 of early-season herbivory. However, no clear compensatory mechanism could
 be identified. While early-season herbivory has the potential to
 affect plant reproduction through changes in plant development or the
 subsequent development of the associated community, these effects were
 small and varied across closely related species. This suggests that plant
 species may be exposed to different levels of natural selection by
 early-season herbivores through plant- or community-mediated effects on
 reproduction.
description: <strong>Herbivore_Community</strong>
 We recorded the development of herbivore communities on the focal
 plants planted in monoculture plots by monitoring individual plants from
 seedling to seed set. Recording of the herbivore communities started two
 days after the experiment was installed. We monitored the development of
 herbivore communities on individual plants by weekly counts early in the
 season and by biweekly counts later in the season. Insects were identified
 <em>in situ</em> to species or family level. If accurate
 identification was not possible, we included the observations as
 morphospecies in our data.
 <strong>Plant_Parameters</strong>
 In addition to observations of the herbivore community, we
 recorded a set of plant parameters as proxies for plant biomass and
 development: plant height (measured from the ground to the top of the
 plant), diameter (measured as the distance between the two most distal
 leaves), the number of true leaves, and the number of flowering and
 seed-carrying branches (aggregated as reproductive branches). The height
 and diameter of plants were used to derive the volume of a cone,
 representing plant biomass as a single volume parameter in the subsequent
 analyses.
 <strong>Seedset_Field</strong> We
 harvested plants after the start of plant senescence but before the
 siliques started losing seeds. From the harvested plants we collected the
 total number of seeds produced as a proxy for plant fitness. For each
 plant, the total number of seeds was estimated by extrapolating the weight
 of 100 seeds to the total seed biomass and rounding to the nearest natural
 number.
 <strong>SeedSet_Tents</strong> The
 same protocol as described above for the field experiment.
 <strong>Analysis</strong> All
 analyses and statistical approaches are detailed in the Functional Ecology
 manuscript. In summary: We applied linear regression to test for effects
 on the different growth and reproduction parameters and followed up on
 this analysis with piecewise structural equation modelling where we test a
 causal hypothesis on how effects of herbivory can cascade to affect seed
 production. Finally, we use multivariate analysis to describe differences
 between plant species in terms of the herbivore communities with which
 they interact.
description: # Quantifying direct and indirect effects of early-season herbivory on
 reproduction across four brassicaceous plant species
 [https://doi.org/10.5061/dryad.c866t1gf7](https://doi.org/10.5061/dryad.c866t1gf7) The data contains observations on the development of four different brassicaceous plant species and their associated herbivore community in a field experiment conducted in the summers of 2017 and 2018 in Wageningen, The Netherlands. These plants were challenged early in their life to herbivory by either caterpillars or aphids or were left untreated. In addition, we include the observed reproductive output on these plants, as well as that of plants that were exposed to the same treatment, but which were grown in a parallel experiment in which herbivore communities were excluded. These data allow us to test whether our herbivory treatments affected plant development and reproduction and whether effects were predominantly mediated by variation in plant growth or variation in the plant-associated herbivore communities. We found that the herbivory treatments affected plant reproduction in the experiment where the herbivore community was excluded. These effects were dependent on the plant species and the herbivore species used. However, no such effects were found in the open-field experiment. The subsequent SEM analyses revealed that variation in plant development was most likely to affect seed production. However, we found that our treatments had little effects on plant development later in the life of plants, indicating that plants were able to attenuate or compensate for these effects. No clear compensatory mechanism could be identified. We conclude that, while early-season herbivory has the potential to affect plant reproduction through changes in plant development, these effects are limited and were similar for the species in this study. As plants are often able to attenuate and compensate the effects of early-season herbivores, the selective potential on plant life-history or defense strategies in our study system seems ubiquitously low. ## Description of the data and file structure The data collected is divided in four ready-to-use excel files to work in conjuncture with the supporting R-scripts (see Code/Software). Our Excel sheets contain a Read-Me explaining the contents of each data sheet, and the type of data collected. The Functional Ecology manuscript has a detailed methods section that outlines data collection and methodology. Identically named columns in the different datasheets link the different data together. For example, the unique identifier "Plant_Code" in the data on plant development relates to the same plant as the unique identifier "Plant_Code" in the data on herbivore community observations and the data on seed production. We appreciate notification of data re-use. Please use the contact [D.Mertens.sci@gmail.com](mailto:d.mertens.sci@gmail.c) and/or [Erik.Poelman@wur.nl](mailto:Erik.Poelman@wur.nl) ## Code/Software All R-code used to analyze the data in this manuscript is published with *zenodo* and can be freely accessed by following the DOI.