DOI: 10.5061/dryad.s7g70j0
title: Data from: Global signal of top-down control of terrestrial plant communities by herbivores

description: The theory of “top-down” ecological regulation predicts that herbivory
 suppresses plant abundance, biomass, and survival but increases diversity
 through the disproportionate consumption of dominant species, which
 inhibits competitive exclusion. To date, these outcomes have been clear in
 aquatic ecosystems but not on land. We explicate this discrepancy using a
 meta-analysis of experimental results from 123 native animal exclusions in
 natural terrestrial ecosystems (623 pairwise comparisons). Consistent with
 top-down predictions, we found that herbivores significantly reduced plant
 abundance, biomass, survival, and reproduction (all P &lt; 0.01) and
 increased species evenness but not richness (P = 0.06 and P = 0.59,
 respectively). However, when examining patterns in the strength of
 top-down effects, with few exceptions, we were unable to detect
 significantly different effect sizes among biomes, based on local site
 characteristics (climate or productivity) or study characteristics (study
 duration or exclosure size). The positive effects on diversity were only
 significant in studies excluding large animals or located in temperate
 grasslands. The results demonstrate that top-down regulation by herbivores
 is a pervasive process shaping terrestrial plant communities at the global
 scale, but its strength is highly site specific and not predicted by basic
 site conditions. We suggest that including herbivore densities as a
 covariate in future exclosure studies will facilitate the discovery of
 unresolved macroecology trends in the strength of herbivore–plant
 interactions.
description: Data_herbiore_meta-analysisThis file contains the mean effect sizes, standard errors, and sample sizes for a variety of plant measurements extracted from studies that compared two types of vegetation plots: those in areas where herbivores were excluded and those in open control areas. Each comparison is linked to a variety of other site and study characteristics. We identified exclosure studies using the following search in the ISI Web of Science database [TS= (exclu* OR exclo* OR insecticide* OR pesticide* OR molluscicide*) AND (forest* OR grassland* OR savann*)] for published between 1980 and November 2016. Studies were included if they met the following criteria: (i) Measured plant vegetation metrics in multiple replicates of both experimental treatments of native herbivore exclusion, either via physical exclosures or pesticides, and in control areas (observational and herbivory simulation studies were excluded); (ii) Located in terrestrial environments broadly classified as natural with vegetation classified as forest, grassland or savanna (we excluded studies from aquatic systems, intertidal areas, wetlands, and disturbed habitats such as clear cut forests, recently burned grasslands, or abandoned fields); (iii) Provided treatment means, sample sizes, and variances, or these could be extracted from the figures using software GetData Graph Digitizer. Version 2.26 (getdata-graph-digitizer.com/). We excluded studies focused on exclusion of non-native, invading, introduced, or domestic species, but we included naturally vegetated sites even if these were hunted, had predator losses or had other selective extinctions, or were selectively logged forests. For studies with repeated measures, we only extracted the final time to capture the possible longest time of the herbivory effects. NPP, net primary productivity.