Vertical stratification of plant-pollinator interactions in a temperate grassland

Abstract

11Interactions between plants and their pollinators vary in time and space at different scales. A neglected aspect of small-scale variation of plant-pollinator interactions is the role of vertical position of flowers. We conducted a series of experiments to study vertical stratification of plant-pollinator interactions in a dry grassland. We observed flower visitors on cut inflorescences of Centaurea scabiosa and Inula salicina placed at different heights above ground in two types of surrounding vegetation: short and tall. Even at such a small-scale, we detected significant shift in total visitation rate of inflorescences in response to their vertical position. In short vegetation, inflorescences close to the ground were visited more frequently, while in high vegetation, inflorescences placed higher received more visits. Moreover, we found major differences in the composition of the pollinator community on flowers at different heights. In a second experiment, we measured flower visitation rate in inflorescences of Salvia verticillata of variable height. Overall flower visitation rate increased markedly with inflorescence height. We also detected a corresponding positive pollinator-mediated selection on increased inflorescence height using data on seed set of individual plants. Overall, our results demonstrate strong vertical stratification of plant-pollinator interactions at the scale of mere decimetres. This may be an important, albeit underappreciated, driver of plant-pollinator coevolution.

Does phenology explain plant–pollinator interactions at different latitudes? An assessment of its explanatory power in plant–hoverfly networks in French calcareous grasslands

“…Indeed, their generalist behaviour, at the species level, could be the result of individually specialized diets, since most pollen retrieved on hoverfly individuals usually comes from a single plant taxon (Lucas et al ) and depends on flower availability and phenology (Cowgill et al , Colley and Luna , Lucas et al ). Moreover, some hoverflies have preferences regarding plant colour, morphology and inflorescence height (Branquart and Hemptinne , Colley and Luna , Lunau , Klecka et al , b).…”

Flower visitation by hoverflies (Diptera: Syrphidae) in a temperate plant-pollinator network

“…Overall, hoverflies seem to visit mostly open bowl-shaped flowers ( Branquart & Hemptinne, 2000 ), where they feed on both nectar and pollen ( Gilbert, 1981 ), but some of them have relatively long proboscises which allow them to reach nectar even in flowers with relatively long spurs ( Gilbert, 1981 ; Vlašánková et al, 2017 ). In addition, inflorescence height also affects flower visitation by some species ( Gervasi & Schiestl, 2017 ; Klecka, Hadrava & Koloušková, 2017 ). It has been recently demonstrated that selective flower visitation by hoverflies can exert a selection pressure strong enough to cause rapid evolutionary shifts in multiple plant traits ( Gervasi & Schiestl, 2017 ; Zu & Schiestl, 2017 ).…”

Water stress and nitrogen supply affect floral traits and pollination in the white mustard,Sinapis alba(Brassicaceae)

“…Pollinator's attraction to a plant depends on visual cues indicating high floral reward such as the number of open flowers (Akter et al, 2017) and the size of floral display (Biella et al, 2019), and on the amount and quality of nectar and pollen (Cresswell, 1999;Grindeland et al, 2005), along with general conspicuousness of the plant which increases its detection by potential pollinators, such as plant height (Junker et al, 2013;Klecka et al, 2018a;Hernández-Villa et al, 2020), local plant clustering (Elliot & Irwin, 2009;Akter et al, 2017), and flower colour (Reverté et al, 2016). Our experiments showed that, these morphological trait differences among the plants had a cascading effect on the number and identity of flower visitors of S. alba and on its reproduction.…”

“…Flower visitation rate of insect-pollinated plants depends on visual cues indicating high floral reward such as the number of open flowers (Conner and Rush, 1996;Akter et al, 2017) and the size of floral display (Grindeland et al, 2005;Parachnowitsch et al, 2010;Biella et al, 2019), and on the amount and quality of nectar and pollen (Cresswell, 1999;Grindeland et al, 2005). Other morphological features can also influence plant detection by potential pollinators, such as plant height (Junker et al, 2013;Klecka et al, 2018a;Hernández-Villa et al, 2020), local plant clustering (Elliot andAkter et al, 2017), and flower colour (Reverté et al, 2016). Measurements of flower visitation with plants grown in the spring 2017 and plants grown in the summer 2018 revealed that and in both cases plants grown with higher amount of water had a significantly higher number of flower visitors compared to plants grown under low amount of water irrespective of nitrogen supply.…”