DOI: 10.5061/dryad.kb0pq
title: Data from: Temporal variability of a single population can determine the vulnerability of communities to perturbations

description: Many aspects of global change affect the variability of species population
 densities, in terms of both the magnitude and pattern of density
 fluctuations. However, we have limited empirical understanding of the
 consequences of altered temporal variability of populations, independent
 of changes in their mean densities, for the structure and stability of
 natural communities and the responses of ecosystems to additional
 stressors. We used a field experiment to test the effects of altered
 temporal variability of a single consumer species on community structure
 and stability. Specifically, we manipulated the temporal variability of
 populations of a key grazer species on temperate rocky shores (Littorina
 littorea), independent of their mean densities, over 12 months and
 measured the responses of algal communities in terms of multiple measures
 of structure and stability. Further, we tested whether consumer
 variability determined the effects of an additional perturbation, elevated
 sedimentation, on algal communities. The effects of sedimentation on the
 structure and stability of algal communities were regulated by the
 temporal variability of consumer populations. In particular, elevated
 sedimentation led to a decrease in algal evenness, but only when consumer
 densities were held constant, and resulted in a decrease in the rate of
 local algal extinctions, but only when consumer temporal variability was
 increased. Independent of sedimentation, increased temporal variability of
 consumer populations led to a shift in algal assemblage structure and
 affected the stability of algal communities in terms of both compositional
 turnover and resistance to environmental perturbations. Further, these
 effects varied according to the temporal pattern of consumer density
 fluctuations. Synthesis. Our results demonstrate that changes in the
 temporal variability of a single species can modify multiple aspects of
 both the structure and stability of natural communities and alter their
 responses to perturbations. However, the effects of consumer variability
 cannot be predicted without knowledge of the temporal pattern of density
 fluctuations. These findings have profound implications for our
 understanding of the effects of multiple disturbances on ecosystems.
description: Algal species
 abundancesSpecies abundance data
 were collected in rocky intertidal habitat on a moderately exposed shore
 at Rush, Co. Dublin, Ireland between August 2012 and August 2013. Column
 headers are as follows: (A) Common headers: "Date" = Sampling
 date (yyyy-mm-dd); "Cage" = Cage present (C1 = caged, using 35 x
 35 cm fence enclosed with lid; C0 = uncaged); "Variability" =
 Consumer (Littorina littorea) variability treatment (Const = constant,
 i.e. maintained at 30 individuals per cage; Var_1 = 'variable1',
 i.e. alternating between 15 and 45 individuals/cage every 2 months; Var_2
 = 'variable2', i.e. alternating between 45 and 15
 individuals/cage every 2 months; Amb = ambient, i.e. unmanipulated in
 uncaged plots); "Sediment" = Sedimentation treatment (S0 =
 ambient, i.e. no additional sediment added; S1 = elevated, i.e. 400 g
 sediment added to plot every month); "Plot_no" = Unique plot
 identifier. (B) 'Macroalgae' datasheet: "Lit_lit_m-2"
 = Adult (&gt;5 mm) Littorina littorea density (per sq. m) within 35 x 35
 cm caged and 25 x 25 cm uncaged plots; Macroalgal species percentage cover
 values, estimated using 25 x 25 cm quadrat with 64 intersections:
 "Lith_spp" = 'Lithothamnia spp.'; "Bry_sp1"
 = Bryopsis sp.; "Cer_shu" = Ceramium shuttleworthianum;
 "Cha_lin" = Chaetomorpha linum; "Cho_cri" = Chondrus
 crispus; "Cla_rup" = Cladophora rupestris; "Cor_off" =
 Corallina officinalis; "Dic_dic" = Dictyota dichotoma;
 "Dum_con" = Dumontia contorta; "Fuc_ves" = Fucus
 vesiculosus; "Gel_pus" = Gelidium pusillum; "Gra_sp1"
 = Gracilaria sp.; "Him_elo" = Himanthalia elongata;
 "Lea_dif" = Leathesia difformis; "Mas_ste" =
 Mastocarpus stellatus; "Osm_spp" = Osmundea spp.;
 "Pol_sp1" = Polysiphonia sp.; "Por_umb" = Porphyra
 umbilicalis; "Ral_ver" = Ralfsia verrucosa; "Ulo_sp1"
 = Ulothrix sp.; "Ulv_int" = Ulva intestinalis;
 "Ulv_lac" = Ulva lactuca. (C) 'Microalgae' datasheet:
 "Sample_no" = Replicate sample (representing one of three
 readings taken per settlement tile fixed within each plot);
 "Total_conc_ug.cm-2" = Total microalgal concentration,
 micrograms per sq. cm, measured using Benthotorch benthic fluorometer (bbe
 Moldaenke GmbH, Germany).Mrowicki et al_Algal abundance
 data.xlsx