Effect of introduced Euphorbia esula on the pollination of Viola pedatifida

Abstract

Introduced plants may compete for pollination with native plants, resulting in reduced fruit or seed set. In this study, I use several techniques to assess whether the invasive plant Euphorbia esula L. (leafy spurge, Euphorbiaceae) reduces the pollination success of chasmogamous flowers of the native plant Viola pedatifida G. Don (prairie violet, Violaceae), which has chasmogamous and cleistogamous flowers. Euphorbia pollen was found on most Viola stigmas, suggesting the potential for competition. Additionally, application of Euphorbia pollen to Viola stigmas prior to conspecific pollen reduced seed set. However, natural receipt of Euphorbia and other heterospecific pollen was not associated with decreased fruit or seed set. In the field, fruit set was higher for Viola in sites with Euphorbia despite increased Euphorbia pollen receipt, and seed set did not vary with the presence of Euphorbia. However, there was no significant interaction between the presence of Euphorbia and flower type (cleistogamous or chasmogamous), suggesting that increased fruit set near Euphorbia is unrelated to pollination. This study suggests that Viola and Euphorbia interact through shared pollinators, but there is no evidence that competition for pollination with Euphorbia reduces Viola's fecundity or results in increased reliance on cleistogamous flowers. Résumé :Les plantes introduites peuvent compétitionner pour la pollinisation avec les plantes indigènes, et entraîner ainsi une réduction des fruits ou des graines. L'auteur a utilisé plusieurs techniques pour déterminer si l'espèce adventice Euphorbia esula L. (euphorbe esule, Euphorbiaceae) réduit le succès de la pollinisation des fleurs chasmogames de la plante indigène Viola pedatifida G. Don (violette des prés) qui possède des fleurs chasmogames et cléistogames. On retrouve le pollen de l'euphorbe sur la plupart des stigmates de la violette, ce qui suggère une compétition potentielle. On observe de plus que l'addition de pollen de l'Euphorbe sur les stigmates de la violette avant une pollinisation conspécifique réduit la production de semences. Au champ, la violette produit plus de fruits sur les sites avec l'euphorbe en dépit d'une augmentation du pollen d'euphorbe reçu, et en présence de l'euphorbe la production de graines ne varie pas. Cependant, il n'y a pas d'interaction significative en présence de l'euphorbe et le type de fleur (cléistogames ou chasmogames), ce qui suggère que l'augmentation de la mise à fruit près de l'euphorbe ne serait pas liée à la pollinisation. Les résultats suggèrent que la violette et l'euphorbe interagissent par le partage de pollinisateurs, mais on n'observe aucune preuve de compétition pour la pollinisation entraînant une réduction de la fécondité de la violette par l'euphorbe ou un recours préférentiel aux fleurs cléistogames.

An Invasive Plant Species Decreases Native Plant Reproductive Success

“…In contrast to other native-invasive plant pollinator interaction studies, where in-vasive plant species pollen is frequently found on the stigma of native plants (Brown et al 2002;Montgomery 2009aMontgomery , 2009b, almost no crown vetch pollen or any other heterospecific pollen grains were found on T. ohiensis. Morales and Traveset (2008) noted that low invasive pollen deposition on native stigmas in invaded areas could be more common than is assumed.…”

“…In the last decade, numerous studies (e.g., Larson et al 2006;Traveset and Richardson 2006 [and citations therein]; Nielsen et al 2008;Montgomery 2009aMontgomery , 2009bDietzsch et al 2011;Thijs et al 2012 [and citations therein]; Sun et al 2013) have addressed the question: Do invasive plant species compete with native plant species for pollinators? These studies have shown negative, positive, and neutral effects regarding the impact of invasive species on the reproduction of native species.…”

Effects of multiple competitors for pollination on bumblebee foraging patterns and Mimulus ringens reproductive success

“…In many flowering plant communities multiple species bloom simultaneously and compete for the service of shared pollinators (Mitchell et al 2009). The consequences of competition for pollination have been well documented for species pairs (Waser 1978, Caruso 2000, Brown et al 2002, Montgomery 2009, Takakura et al 2009), but have received much less attention in more diverse plant communities (but see Ghazoul 2006, Lopezaria‐Mikel et al 2007, Lazaro et al 2009). Several studies of interspecific competition for abiotic resources have demonstrated that competitive outcomes may not be a simple additive function of pair‐wise interactions (Miller 1994, Dormann and Roxburgh 2005, Weigelt et al 2007, Perkins et al 2007).…”

Spatial variation of pollen receipt and effects of heterospecific pollen on seed set in Salvia przewalskii

“…In contrast to manipulative experiments, observations of HP incidence under natural pollination regimes have revealed that quantities of HP received tend to be variable and from diverse donor species (Emer et al, 2015 ; Fang & Huang, 2013 ; Johnson & Ashman, 2019 ; Montgomery & Rathcke, 2012 ; Wei et al, 2021 ; Zhang et al, 2021 ). Consequently, effects may differ between manipulative studies and those investigating natural variation (e.g., Montgomery, 2009 ). Studies that evaluated the impact of natural HP receipt on plant reproduction in the field have observed no detrimental effect of HP (Montgomery, 2009 ), negative effects on conspecific pollen‐tube success (Parra‐Tabla et al, 2020 ), or negative interaction between conspecific pollen (CP) and HP quantities, with the effect of CP on seed production becoming weaker with larger quantities of HP deposition (Briggs et al, 2016 ).…”

“…Consequently, effects may differ between manipulative studies and those investigating natural variation (e.g., Montgomery, 2009 ). Studies that evaluated the impact of natural HP receipt on plant reproduction in the field have observed no detrimental effect of HP (Montgomery, 2009 ), negative effects on conspecific pollen‐tube success (Parra‐Tabla et al, 2020 ), or negative interaction between conspecific pollen (CP) and HP quantities, with the effect of CP on seed production becoming weaker with larger quantities of HP deposition (Briggs et al, 2016 ). Moreover, because the composition of co‐flowering species and pollinators can differ greatly across communities, different populations of the same species may receive HP from different donor species (Herrera, 1988 ; Johnson & Ashman, 2019 ), which suggests that the effects of HP receipt may vary among populations across a species' range.…”