Does competition with wind‐pollinated species alter Echium plantagineum's attractiveness to a common pollinator Bombus terrestris?

Abstract

1. In insect-pollinated plants, pollinator attraction is influenced by flowers (e.g. number, size) and their associated rewards (e.g. pollen, nectar). These traits can depend on plant interactions. Indeed, below-ground competition between plants can lead to a decrease in flower or reward production in insect-pollinated species. 2. Wind-pollinated plants, in particular, which are almost never studied in plant-pollinator networks, can alter insect-pollinated plants' attractiveness through competition for nutrients. The response of pollinators to such changes has never been investigated. 3. A pot experiment was carried out in which an insect-pollinated species, Echium plantagineum, was grown in binary mixture with three wind-pollinated species selected to exert a panel of competitive interactions. Below-ground competition was controlled using dividers limiting interspecific root competition. Floral traits of E. plantagineum (i.e. flower production, floral display size, flower size and nectar production) were measured. For each species mixture, the visits (i.e. first visit, number of visits, 10-min sequences) of Bombus terrestris individuals released in a flight cage containing two pots were followed, one with and one without below-ground competition. 4. Below-ground competition significantly affected nectar's sucrose concentration but did not influence flower and nectar production. Likewise, pollinator visits were not influenced by below-ground competition. Competitor identity significantly influenced flower and reward production of E. plantagineum, with a decrease in the presence of the most competitive wind-pollinated species. A tendency for faster flower visitation events was also detected in the presence of the least competitive competitor. This study raises new questions regarding the influence of wind-pollinated plants on plant-pollinator interactions.

Below-ground competition alters attractiveness of an insect-pollinated plant to pollinators

“…plant probability of displaying flowers, plant floral display size, flower size) distance were negatively influenced by the competition treatment. This has been observed in previous studies, especially at the plant level ( Baude et al 2011 ; Partzsch and Bachmann 2011 ; Flacher et al 2015 , 2017 ) probably through soil resource depletion as floral traits can be sensitive to soil resource availability ( Muñoz et al 2005 ; Burkle and Irwin 2009 ). In contrast, reward traits such as nectar volume and concentration remained constant regardless of the competitive context.…”

“…By measuring plant biomass, we assessed the competition outcome rather than the competition itself ( Trinder et al 2012 ). Nevertheless, Flacher et al (2015 , 2017 ) showed that H. lanatus plants can display a large and dense root system that can lead to a reduction of their neighbour’s biomass. Moreover, plant size and biomass can lead to some advantages especially for the occupation of soil space and nutrient acquisition ( Berntson and Wayne 2000 ; Raynaud and Leadley 2004 ; Gurevitch et al 2006 ).…”

“…This is likely due to changes in plant access to nutrients as plant competition can influence their local availability ( Berntson and Wayne 2000 ; Raynaud and Leadley 2004 ). Moreover, Flacher et al (2015 , 2017 ) found that the impact of competitive interactions between plants on attractiveness traits was stronger as the intensity of competition increased. At the plant community level, the attractiveness of an individual plant may depend on its own floral traits but also on floral traits of neighbouring plant individuals or species ( Willmer 2011 ).…”

“…Likewise, when focusing on plant–pollinator interactions, competition between plants can affect floral parameters of insect-pollinated plants, such as floral display size, flower production or nectar quantity and quality ( Baude et al 2011 ; Partzsch and Bachmann 2011 ; Flacher et al 2015 , 2017 ). This is likely due to changes in plant access to nutrients as plant competition can influence their local availability ( Berntson and Wayne 2000 ; Raynaud and Leadley 2004 ).…”

Long‐term experimental drought alters floral scent and pollinator visits in a Mediterranean plant community despite overall limited impacts on plant phenotype and reproduction

“…Therefore, floral scent is highly sensitive to increased temperature (Farré‐Armengol et al, 2014; Yuan et al, 2009) and drought, with increased emissions under moderate stress (Burkle & Runyon, 2016; Campbell et al, 2019; Glenny et al, 2018). Altered floral attractiveness could therefore affect pollinators' foraging behaviour and resource choices (Flacher et al, 2017, 2020). For instance, herbivore‐induced plant volatiles present in floral scent tend to deter pollinators from floral resources in attacked plants (Hoffmeister & Junker, 2017; Kessler et al, 2011).…”