DOI: 10.5061/dryad.hqbzkh1wk
title: Butterfly host plant use driven by microclimate not nutritional quality

description: The abundance of insect herbivores often depends on host plant suitability
 for their specialised immature stages. Suitability can be strongly
 influenced by both microclimate and the nutritional quality of the plants
 themselves. Where soil nitrogen is high, host plants tend to have high
 nutritional quality, but vigorous growth of surrounding vegetation reduces
 microclimatic temperatures. Thus, thermophilous insects may face a choice
 between host plants with optimal microclimates and those with optimal
 nutritional quality. We investigated how microclimate and nitrogen content
 influence oviposition choices by the declining Small Copper butterfly,
 Lycaena phlaeas, on its host plant, Rumex acetosa. We predicted that
 warmer plants would have lower nitrogen content, and that butterflies
 would choose cooler, high-nitrogen plants during warmer ambient
 conditions. Although warmer R. acetosa plants had lower nitrogen content,
 L. phlaeas consistently chose to lay eggs on plants in warm microclimates,
 implying a trade-off between temperature and the nutritional quality of
 host plants. Patches of bare ground created by European Moles (Talpa
 europaea) near R. acetosa plants increased microclimatic temperatures and
 decoupled the negative correlation between nutritional quality and thermal
 suitability. Our results have implications for the conservation of
 thermophilous insect herbivores, especially close to their range margins
 and in the context of climate change. Rather than maximising host plant
 abundance or nutritional quality, management that creates suitable
 microclimatic conditions is likely to be critical. Our findings also
 suggest that, while nitrogen pollution may increase host plant nutritional
 quality, its negative impacts on microclimate will likely further reduce
 breeding habitat for L. phlaeas and other insects in grassland habitats.
description: # Butterfly host plant use driven by microclimate not nutritional quality
 Dataset DOI:
 [10.5061/dryad.hqbzkh1wk](https://doi.org/10.5061/dryad.hqbzkh1wk) ##
 Description of the data and file structure Data collected to support
 investigations into the role of microclimate around host plants and
 nutritional quality of host plants in shaping oviposition by a specialist
 herbivorous butterfly.  Each row in the dataset is a host plant, either a
 plant with one or more eggs or larvae (plant_id contains 'e') or
 a control plant next to an occupied plant (in a randomly selected
 direction) (plant_id contains 'c').  There are two datasets, one
 smaller dataset (plant chemistry data) which contains chemical data for a
 sample of host plants along with data on possible proxies for this
 chemical data. This data was used to identify the best proxies for host
 nutritional quality (nitrogen content). The second larger dataset was then
 used for all further analyses. It contains data about host plant chemistry
 proxies, predicted host plant chemistry, the environment around them, the
 presence of butterfly eggs and larvae.  The plants in the first dataset
 are largely a subset of those represented in the second, but several
 plants in the smaller dataset were later removed from the main analysis,
 and retained for the proxy analysis, hence the separate datasets. ###
 Files and variables #### File: egg_laying_data.csv **Description:**  #####
 Variables * predicted_n: Predicted nitrogen content of host plant,
 micromoles per g. * n_se: standard error around predicted nitrogen content
 of host plant. * n_weights: inverse of standard error around predicted
 nitrogen content of host plant. * plant_id: unique identifier for host
 plant, a 'c' denotes a control plant, and 'e' a plant
 with butterfly eggs or larvae. * id_number: numeric component of plant_id
 * species: host plant species, all ra as all host plants were Rumex
 acetosa. * season: season in which host plant was sampled, either autumn
 or spring (referred to as early summer in manuscript). * n_eggs: number of
 eggs on plant * larvae: number of larvae on plant * occupied: whether the
 plant was occupied with butterfly eggs or larvae (based on preceding two
 columns). * gps: British national grid reference of host plant *
 bare_ground: %cover of bare ground around host plant, in 50cm grid with
 host plant at centre. * veg: %cover of vegetation around host plant, in
 50cm grid with host plant at centre. * litter: %cover of litter around
 host plant, in 50cm grid with host plant at centre. * sward_height: sward
 height (cm) around host plant, measured using direct method (see
 manuscript). * plant_area: estimated area of host plant (in cm^2^, based
 on perpendicular dimensions of tightest fitting square - plant_size_1
 multiplied by plant_size_2) * bare: whether or not bare ground was present
 in the 50cm grid around the host plant. * plant_size_1: One dimension of
 plant used to calculate plant area (cm). * plant_size_2:  One dimension of
 plant used to calculate plant area (cm). * leaf1_length: Length of a
 sampled leaf used to calculate leaf area and average ultimately leaf size
 (mm). * leaf2_length: Length of a sampled leaf used to calculate leaf area
 and average ultimately leaf size (mm). * leaf3_length: Length of a sampled
 leaf used to calculate leaf area and average ultimately leaf size (mm). *
 leaf1_width: Width of a sampled leaf used to calculate leaf area and
 average ultimately leaf size (mm). * leaf2_width: Width of a sampled leaf
 used to calculate leaf area and average ultimately leaf size (mm). *
 leaf3_width: Width of a sampled leaf used to calculate leaf area and
 average ultimately leaf size (mm). * leaf1_area: Area of a sampled leaf
 (mm^2^). * leaf2_area: Area of a sampled leaf (mm^2^). * leaf3_area: Area
 of a sampled leaf (mm^2^). * total_leaf_area: Sum of areas of sampled
 leaves (mm^2^). * leaves_sampled: Number of leaves from host plant sampled
 * average_leaf_size: Average area of sampled host plant leaves (mm^2^) *
 temperature_soil: Temperature measured at soil surface under host plant
 (degrees Celsius). * temperature_ambient: Ambient temperature measured
 while measuring soil surface temperature under host plant (degrees
 Celsius). * environment_date: Date on which environmental measurements for
 host plant were taken. * temperature_date: Date on which temperature
 measurements for host plant were taken. * date_mean_soil: Mean soil
 surface temperature of host plants measured on the same date as plant in
 that row. * date_sd_soil: Standard deviation of soil surface temperatures
 of host plants measured on the same date as plant in that row. *
 temperature_soil_scaled: Soil surface temperature under host plant, scaled
 and centred by sampling date to express whether a host plant was warmer or
 cooler than others measured on the same date. * scaled_leaf_size: Centred
 and scaled average leaf area for host plant. * scaled_n_content: Centred
 and scaled predicted nitrogen content for a host plant. #### File:
 plant_chemistry_data.csv **Description:**  ##### Variables * plant_id:
 Unique identifer of host plant. * N: % nitrogen content of host plant by
 mass * C: % carbon content of host plant by mass * cn_percent: Carbon :
 Nitrogen ratio of host plant by mass * n_molar: Molar nitrogen content of
 host plant (micromoles per g). * c_molar: Molar carbon content of host
 plant (micromoles per g). * cn_molar: Molar Carbon : Nitrogen ratio of
 host plant * plant_size_1: One dimension of plant used to calculate plant
 area (cm). * plant_size_2:  One dimension of plant used to calculate plant
 area (cm). * plant_area: Estimated area of host plant (in cm^2^, based on
 perpendicular dimensions of tightest fitting square - plant_size_1
 multiplied by plant_size_2) * leaf1_length: Length of a sampled leaf used
 to calculate leaf area and average ultimately leaf size (mm). *
 leaf1_width: Width of a sampled leaf used to calculate leaf area and
 average ultimately leaf size (mm). * leaf2_length: Length of a sampled
 leaf used to calculate leaf area and average ultimately leaf size (mm). *
 leaf2_width: Width of a sampled leaf used to calculate leaf area and
 average ultimately leaf size (mm). * leaf3_length: Length of a sampled
 leaf used to calculate leaf area and average ultimately leaf size (mm). *
 leaf3_width: Width of a sampled leaf used to calculate leaf area and
 average ultimately leaf size (mm). * leaf1_area: Area of a sampled leaf
 (mm^2^). * leaf2_area: Area of a sampled leaf (mm^2^). * leaf3_area: Area
 of a sampled leaf (mm^2^). * total_leaf_area: Sum of areas of sampled
 leaves (mm^2^). * leaves_sampled: Number of leaves from host plant sampled
 * average_leaf_size: Average area of sampled host plant leaves (mm^2^) *
 season: Season in which host plant was sampled, autumn or spring (early
 summer in manuscript). * quality_PC1: Value of first principal component
 of PCA of average leaf size and plant area for host plant. *
 quality_PC2: Value of second principal component of PCA of average leaf
 size and plant area for host plant. ## Code/software Datasets viewed in
 Microsoft excel, and analysed using R and R studio.