Schematic diagram resuming the results.

<p>(a) Total visitation rate, (b) visitation rate excluding the honeybee and (c) fructification in <i>Leopoldia</i> target plants. The non-native <i>Hedysarum</i> is represented in black while the native <i>Leopoldia</i> is represented in grey. Grey continuous arrows represent the overall effect of <i>Hedysarum</i> on <i>Leopoldia</i> target plants while black continuous and dashed arrows represent direct and indirect effects, respectively. The sign of the effect is given in brackets next to each arrow. Whether the effect is mediated by the vegetative parts (vegetative interaction) or by the floral display of <i>Hedysarum</i>, is indicated by coloring the part involved in the effect and leaving the not involved in bold.</p

Direct and Indirect Influence of Non-Native Neighbours on Pollination and Fruit Production of a Native Plant

<div><p>Background</p><p>Entomophilous non-native plants can directly affect the pollination and reproductive success of native plant species and also indirectly, by altering the composition and abundance of floral resources in the invaded community. Separating direct from indirect effects is critical for understanding the mechanisms underlying the impacts of non-native species on recipient communities.</p><p>Objectives</p><p>Our aims are: (a) to explore both the direct effect of the non-native <i>Hedysarum coronarium</i> and its indirect effect, mediated by the alteration of floral diversity, on the pollinator visitation rate and fructification of the native <i>Leopoldia comosa</i> and (b) to distinguish whether the effects of the non-native species were due to its floral display or to its vegetative interactions.</p><p>Methods</p><p>We conducted field observations within a flower removal experimental setup (i.e. non-native species present, absent and with its inflorescences removed) at the neighbourhood scale.</p><p>Results</p><p>Our study illustrates the complexity of mechanisms involved in the impacts of non-native species on native species. Overall, <i>Hedysarum</i> increased pollinator visitation rates to <i>Leopoldia</i> target plants as a result of direct and indirect effects acting in the same direction. Due to its floral display, <i>Hedysarum</i> exerted a direct magnet effect attracting visits to native target plants, especially those made by the honeybee. Indirectly, <i>Hedysarum</i> also increased the visitation rate of native target plants. Due to the competition for resources mediated by its vegetative parts, it decreased floral diversity in the neighbourhoods, which was negatively related to the visitation rate to native target plants. <i>Hedysarum</i> overall also increased the fructification of <i>Leopoldia</i> target plants, even though such an increase was the result of other indirect effects compensating for the observed negative indirect effect mediated by the decrease of floral diversity.</p></div

Ranges (min and max values) of main characteristics of 1 m radius neighbourhoods around <i>Leopoldia</i> target plants according to the presence of non-native <i>Hedysarum</i> plants: (i) Control, <i>Hedysarum</i> plants absent; (ii) Invaded, <i>Hedysarum</i> flowering plants present; and (iii) Removal, <i>Hedysarum</i> plants with clipped inflorescences but intact vegetative parts present.

<p>* Total number of flowers observed during the study</p><p>Ranges (min and max values) of main characteristics of 1 m radius neighbourhoods around <i>Leopoldia</i> target plants according to the presence of non-native <i>Hedysarum</i> plants: (i) Control, <i>Hedysarum</i> plants absent; (ii) Invaded, <i>Hedysarum</i> flowering plants present; and (iii) Removal, <i>Hedysarum</i> plants with clipped inflorescences but intact vegetative parts present.</p

Schematic diagram on direct, indirect and overall effects.

<p>Effects of a non-native plant (black) on the visitation rate and fructification of a native target neighbour plant (grey). The overall effect (continuous grey arrow) can be the result of direct (continuous black arrow) and indirect (dashed black arrows) effects. The specific questions outlined in this study correspond to the numbered arrows.</p

dataset_MonteroCastaño&Vila_FunctionalEcology_2016

dataset_MonteroCastaño&Vila_FunctionalEcology_201

Effect of <i>Hedysarum</i> and the floral diversity on the pollination and reproductive success of <i>Leopoldia</i>.

<p>Mean + SE (a) total pollinator visitation rate (i.e. visits/flower/hour), (b) pollinator visitation rate excluding the honeybee and (c) fructification (i.e. proportion of observed flowers that set fruit) in <i>Leopoldia</i> target plants in Control (grey bar), Invaded (black) and Removal (bold) neighbourhood treatments. Significant differences are represented by different letters above bars according to the 95% confidence intervals of the estimates obtained for the <i>post hoc</i> multilevel comparisons conducted for the models, which included the floral diversity and the density of flowers as covariates.</p

Pollinator species and visits (%) to native <i>Leopoldia</i> plants in the study area during 147 censuses (36.75 h).

<p>Species in bold letters are the ones shared with non-native <i>Hedysarum</i> plants (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0128595#pone.0128595.s003" target="_blank">S3 Table</a>). Total number and percentage (in brackets) of visits achieved by each pollinator species in each neighbourhood treatment are also given.</p><p>Pollinator species and visits (%) to native <i>Leopoldia</i> plants in the study area during 147 censuses (36.75 h).</p

Appendix A. Location of Hypericum perforatum seed source populations sampled in North America and Europe.

Location of Hypericum perforatum seed source populations sampled in North America and Europe

Behaviours of <i>Flavipanurgus venustus</i> on <i>Cistus crispus</i> flowers.

<p>(a) Males (unusually large head with yellow face and big mandibles) spend most of their time patrolling and defending areas of few square metres with abundant C. crispus flowers, often waiting for females landed on petals; (b) occasionally, they feed on C. crispus pollen and nectar; (c-d) females (small head with black face) spend most of their time visiting C. crispus flowers and collecting pollen loads in their scopa for provisioning the brood cells; (e) males (see top-left corner) approach females that are feeding in their territory and (f) copulate with them (notice that in the photo the wings of the male are closed while the wings of the female are open); (g) after the copula, males remain territorial waiting for other females. The body length is 8–10 mm. Notice that males and females touch both anthers and stigmas. Photos: J.P. González-Varo.</p

Relationship between the density of <i>Flavipanurgus venustus</i> and that of <i>Cistus crispus</i> flowers in the study woodland patches.

<p><i>n</i>_total = 38 ‘woodland patch × year’ combinations; orange, purple and blue circles are 2011 (<i>n</i> = 15 patches), 2012 (<i>n</i> = 13) and 2013 (<i>n</i> = 10) data, respectively. The large panel shows bee densities predicted by the model that included the sampling date (Julian day) as covariate. The inset represents the observed bee densities (same scale as the large panel in both axes).</p