DOI: 10.5061/dryad.s7h44j1mr
title: Bottom-up and top-down drivers influence urbanization effects on insect herbivory in oaks

description: Urban forests provide essential ecosystem services. Herbivory is a
 widespread biotic interaction that shapes ecosystem functions, which
 underpin these services. Urbanization disrupts plant-herbivore
 interactions by altering plant traits (bottom-up factors) or by changing
 the abundance of herbivore natural enemies (top-down control), potentially
 threatening the services provided by urban forests. Disentangling these
 drivers of herbivory is crucial for designing and managing urban forests
 to enhance resilience. We examined insect leaf herbivory on Quercus robur
 trees in urban and rural forest stands across 13 European cities (N = 104
 trees). To assess the effects of top-down forces on herbivory, we excluded
 vertebrate (e.g., birds, bats), invertebrate (e.g., ants), or both groups
 of predators from branches on each tree. We then measured insect damage on
 the different treatments. We also assessed bottom-up drivers by measuring
 leaf traits, specifically nutrients and phenolic compounds, and tested for
 correlations with leaf damage. Additionally, we recorded temperature
 within stands, an abiotic factor that may modulate both top-down and
 bottom-up forces on herbivory. Herbivory was 24% lower on urban trees
 compared to rural trees. Excluding vertebrate predators increased
 herbivory by 40%, with effects being stronger in urban stands.
 Additionally, urban trees had higher leaf quality, with higher nutrient
 and lower phenolic concentrations; however, the measured traits did not
 correlate with herbivory. Finally, temperature was positively associated
 with urbanization and correlated with predation (positively), but not with
 herbivory. Temperature also did not mediate the bottom-up or top-down
 effects of urbanization on herbivory. Urbanization affects herbivory
 through both bottom-up and top-down processes, independent of local
 temperature. Despite stronger predator effects and better leaf quality,
 urban trees experience lower herbivory, suggesting that unmeasured
 factors, such as changes in herbivore behaviour or community structure,
 may play an important role. Further studies are needed to deepen our
 understanding and inform urban forest management.
description: # Bottom-up and top-down drivers influence urbanization effects on insect
 herbivory in oaks Dataset DOI:
 [10.5061/dryad.s7h44j1mr](https://doi.org/10.5061/dryad.s7h44j1mr) ##
 Description of the data and file structure In this study, we examined
 insect leaf herbivory on *Quercus robur* trees in urban and rural forest
 stands across 13 European cities (N = 104 trees). To assess the effects of
 top-down forces on herbivory, we excluded vertebrate (e.g., birds, bats),
 invertebrate (e.g., ants), or both groups of predators from branches on
 each tree. We then measured insect damage on the different treatments. We
 also assessed bottom-up drivers by measuring leaf traits, specifically
 nutrients and phenolic compounds, and tested for correlations with leaf
 damage. Additionally, we recorded temperature within stands, an abiotic
 factor that may modulate both top-down and bottom-up forces on herbivory.
 ### Files and variables #### File: clima.csv **Description:** At the
 beginning of the growing season, we installed an *Elitech RC-5* data
 logger (Elitech, London, UK) 1.5 meters above the ground on a tree in each
 stand to quantify air temperature. This file contains the daily mean
 temperature for each stand in each city (26 stands across 13 cities) #####
 Variables * date: Day when the data were collected * meantemp: Daily mean
 temperature (°C) of the stand * Urb: Urban or rural stands within each
 site * Site: City (among 13 European cities) #### File: data.csv
 **Description:** Chewing herbivory data estimated by calculating the
 percentage of leaf area removed from each leaf by using the **BioLeaf –
 Foliar Analysis^TM^** mobile app. Missing values: \- "n/a"
 indicates cases where no measurement was taken because insufficient leaf
 material was available for analysis in that treatment. ##### Variables *
 ID: Unique identifier for each sample * Site: City (among 13 European
 cities) * T: Branch treatment (Ant-excluded, Bird-excluded, Both, Control)
 * Urb: Urban or rural stands within each site * Tree: Tree number (4 trees
 per stand) * L1-L10: Individual leaf herbivory values (% leaf area
 removed) * herbivory: Mean leaf herbivory per branch #### File:
 nutrients.csv **Description:** Leaf nitrogen (N) and phosphorus (P)
 concentrations. Nitrogen was quantified using the indophenol blue method,
 and phosphorus using the molybdenum blue method, with absorbance measured
 at 650 nm and 700 nm, respectively, using a Biorad 650 microplate reader
 [(Walinga et al., 1995)](https://www.zotero.org/google-docs/?6HZU5R). Both
 concentrations were expressed in mg g⁻¹ dry tissue. ##### Variables * ID:
 Sample number * Site: City (among 13 European cities) * T: Branch
 treatment (Ant-excluded, Bird-excluded, Both, Control) * Urb: Urban or
 rural stands within each site * Tree: Tree number (4 trees per stand) * P:
 Phosphorus concentration (mg g⁻¹) * N: Nitrogen concentration (mg g⁻¹)
 #### File: phenolics.csv **Description:** For each tree, we selected four
 leaves (out of the ten originally sampled) from control branches showing
 little or no herbivore damage for measuring phenolic compounds
 by UHPLC equipped with a UV/VIS photodiode array detector. Analysis
 focused on: flavonoids, phenolic acids, hydrolysable tannins, condensed
 tannins, and total phenolics. All concentrations were expressed in mg g⁻¹
 of dry tissue. **Missing values:** * "n/a" indicates that the
 measurement was below the detection limit of the instrument, and
 therefore, no quantitative value could be reported for the specific
 compound. ##### Variables * ID: Sample number * Site: City (among 13
 European cities) * T: Branch treatment (Ant-excluded, Bird-excluded, Both,
 Control) * Urb: Urban or rural stands within each site * Tree: Tree number
 (4 trees per stand) * F1-F8: Individual flavonoid compound concentration
 (mg g⁻¹) * PA1-PA3: Individual phenolic acid concentration (mg g⁻¹) * CT:
 Condensed tannin concentration (mg g⁻¹) * HT1-HT5: Hydrolysable
 tannin concentration (mg g⁻¹) * flav: Total flavonoid concentration (mg
 g⁻¹) * phen_acids: Total phenolic acid concentration (mg g⁻¹) *
 condensed_tannins: Total condensed tannin concentration (mg g⁻¹) *
 hydrolysable_tannins: Total hydrolysable tannin concentration (mg g⁻¹) *
 total: Total phenolic concentration (mg g⁻¹) #### File:
 URBANIZATION_DATA_ANALYSIS_OIKOS.Rmd **Description:** R Markdown document
 containing the code used for data analysis and figure generation in this
 study. ## Code/software All statistical procedures were carried out in R
 version 4.2.1 (R Core Team, 2024). The R Markdown file
 "URBANIZATION_DATA_ANALYSIS_OIKOS.Rmd" contains all the
 necessary code to replicate the results of the study, including loading
 the data sets, performing data manipulations, creating subsets for
 analysis, and running all the models.