DOI: 10.5061/dryad.5r2p2
title: Data from: Experimentally reducing species abundance indirectly affects food web structure and robustness

description: Studies on the robustness of ecological communities suggest that the loss
 or reduction in abundance of individual species can lead to secondary and
 cascading extinctions. However, most such studies have been
 simulation-based analyses of the effect of primary extinction on food web
 structure. In a field experiment we tested the direct and indirect effects
 of reducing the abundance of a common species, focusing on the diverse and
 self-contained assemblage of arthropods associated with an abundant
 Brazilian shrub, Baccharis dracunculifolia D.C. (Asteraceae). Over a
 5-month period we experimentally reduced the abundance of Baccharopelma
 dracunculifoliae (Sternorrhyncha: Psyllidae), the commonest galling
 species associated with B. dracunculifolia, in 15 replicate plots paired
 with 15 control plots. We investigated direct effects of the manipulation
 on parasitoids attacking B. dracunculifoliae, as well as indirect effects
 (mediated via a third species or through the environment) on 10 other
 galler species and 50 associated parasitoid species. The experimental
 manipulation significantly increased parasitism on B. dracunculifoliae in
 the treatment plots, but did not significantly alter either the species
 richness or abundance of other galler species. Compared to control plots,
 food webs in manipulated plots had significantly lower values of weighted
 connectance, interaction evenness and robustness (measured as simulated
 tolerance to secondary extinction), even when B. dracunculifoliae was
 excluded from calculations. Parasitoid species were almost entirely
 specialized to individual galler species, so the observed effects of the
 manipulation on food web structure could not have propagated via the
 documented trophic links. Instead, they must have spread either through
 trophic links not included in the webs (e.g. shared predators) or
 non-trophically (e.g. through changes in habitat availability). Our
 results highlight that the inclusion of both trophic and non-trophic
 direct and indirect interactions is essential to understand the structure
 and dynamics of even apparently discrete ecological communities.
description: Galler and parasitism
 dataData from an
 experimental manipulation on galler species and their parasitoids on the
 host plant species Baccharis dracunculifolia, carried out in Serra do
 Cipó, Minas Gerais state, south east Brazil. In the experiment the
 abundance of galler M7 was reduced in the replicated exclusion treatment
 plots. (Paras = parasitoid; paras_corrected = parasitism was corrected
 where parasitoids were gregarious so that the proportion parasitised was
 never more than 1)Barbosa_Galler_and_Parasitism_data_DRYAD.xlsxFood Web MetricsData from an experimental manipulation on galler-parasitoid food webs on the host plant species Baccharis dracunculifolia, carried out in Serra do Cipó, Minas Gerais state, south east Brazil. In the experiment the abundance of galler M7 was reduced in the replicated exclusion treatment plots. Food web metrics are shown for food webs including and excluding the manipulated galler M7.Barbosa_Food_Web_Metrics_data_DRYAD.xlsx