DOI: 10.5061/dryad.tqjq2bw67
title: Overabundant populations of large wild herbivores disrupt plant-pollinator networks in a Mediterranean ecosystem

description: Large herbivores are keystone species, so changes in their population
 abundance may cause cascading effects on ecosystems. Our study explores
 the impacts of increasing red deer (Cervus elaphus) densities on
 plant-pollinator networks. We conducted a manipulative experiment with
 increasing densities, consisting of comparable hectare-scale enclosures in
 a Mediterranean ecosystem. We simulated two current scenarios of deer
 overabundance: high densities (&gt;30 individuals/km2) and hyper
 densities (&gt;90 individuals/km2). We compared these scenarios to an
 adjacent control exclosure (no deer). In each scenario we analysed
 herbivory in three focal species of shrub, as well as flower and
 pollinator abundance, richness, diversity, evenness, and composition. We
 also analysed plant-pollinator interaction dissimilarity among networks,
 plant visitation rate, as well as plant and pollinator generality. For
 each network, we analysed network size, interaction richness, diversity,
 and evenness, as well as network connectance, specialization, nestedness,
 modularity, modules, and robustness. We found that herbivory reduced
 flower abundance of scrubs, as well as flowering plant and pollinator
 richness. Remaining plants and pollinators lost interactions, and some
 plants lost pollinator visitors. Network specialization and modularity
 decreased because modules (groups of species strongly connected) conformed
 by herbs and specialist pollinators were gradually extirpated as deer
 density increased. This simplification increased network connectance and
 nestedness. Network robustness (a measure of stability) remained unaltered
 because the dominant plant, which attracted most pollinators, was
 unpalatable to deer. We conclude that in overabundant deer scenarios: 1)
 impact on plant-pollinator networks will increase with deer density; 2)
 plant-pollinator networks will be eroded, especially if they are composed
 of palatable, rare plants, visited by specialist pollinators; and 3)
 plant-pollinator network stability will be unaffected if dominant plants
 are generalists and unpalatable to deer. All this information enables to
 replicate all the analyses present in the manuscript, as well as to
 describe or explore other aspects of the study system. Please, have a look
 in the README file before exploring or using the data. If you have any
 questions, please contact the author. This dataset is part of a long-term
 (&gt;4 years) experiment, so may be updated in the forthcoming years.
 If you are interested in using the data of this study or the data of the
 long-term experiment for your research, please contact the author. I will
 be happy to collaborate.
description: # Overabundant populations of large wild herbivores disrupt
 plant-pollinator networks in a Mediterranean ecosystem Dataset DOI:
 [10.5061/dryad.tqjq2bw67](10.5061/dryad.tqjq2bw67) ## Description of the
 data and file structure We conducted a manipulative experiment with
 increasing densities, consisting of comparable hectare-scale enclosures in
 a Mediterranean ecosystem. We simulated two current scenarios of deer
 overabundance: high densities (&gt;30 individuals/km2) and hyper densities
 (&gt;90 individuals/km2). We compared these scenarios to an adjacent
 control exclosure (no deer). In each scenario we analysed herbivory in
 three focal species of shrub, as well as flower and pollinator abundance,
 richness, diversity, evenness, and composition. We also analysed
 plant-pollinator interaction dissimilarity among networks, plant
 visitation rate, as well as plant and pollinator generality. For each
 network, we analysed network size, interaction richness, diversity, and
 evenness, as well as network connectance, specialization, nestedness,
 modularity, modules, and robustness. ### Files and variables All the
 databases of the study are present here: -"herbivory.txt".
 herbivory on the three focal plants (semiquantitative measure (range 0-5)
 following Perea et al. 2015) -"plant_community.txt". plant
 community composition (flower abundance of each species) -"plant
 individuals.txt" number of individuals of the two subdominant focal
 plants -"pollinator_community.txt". pollinator community
 composition (number of individuals of each species) -"visitation
 rate.txt". visitation rate of the three focal plants (observed
 pollinator individuals/100 observed flowers) -plant-pollinator networks, 3
 for each treatment ("nw_qc1.txt", "nw_qc2.txt",
 "nw_qc3.txt", "nw_qdb1.txt", "nw_qdb2.txt",
 "nw_qdb3.txt", "nw_qda1.txt", "nw_qda2.txt",
 "nw_qda3.txt"). Each network is an adjacency matrix in which
 files are plants, columns are pollinators, and cell value is interaction
 frequency (standardised number of visits a given pollinator visited a
 given plant). -the metanetwork for each treatment (3 local networks pooled
 together; "metaweb_C.txt", "metaweb_dB.txt",
 "metaweb_dA.txt") -the metanetwork for the whole study system (3
 metanetworks pooled together; "metaweb.txt") All this
 information enables to replicate all the analyses present in the
 manuscript, as well as to describe or\ explore other aspects of the study
 system. Please note that some codes and abbreviations are used in the
 databases for convenience: TREATMENT CODES C: Control\ dB: High Density\
 dA: Hyper Density SPECIES ABBREVIATIONS Clad: Cistus ladanifer\ Cpop:
 Cistus populifolius\ Tmas: Thymus mastichina Usage note: You can easily
 open this files with Excel or R (R Core Team 2025) to conduct descriptive
 statistics. You may use the package vegan (Oksanen et al. 2025) to
 visualize community data, and the package bipartite (Dormann 2025) to
 visualize networks.