The most effective pollinator revisited: pollen dynamics in a spring-flowering herb

Marcin Zych,Katarzyna Roguz,Jan Goldstein,Małgorzata Stpiczyńska

doi:10.1007/s11829-013-9246-3

Marcin Zych, Katarzyna Roguz + Show 2 more

Open Access

https://doi.org/10.1007/s11829-013-9246-3

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Abstract

Most flowers are visited by a wide range of potential pollinators. However, their efficiency in pollen removal and deposition, and other behavioural factors affecting pollination effectiveness may greatly differ among taxa, and even individuals. Fritillary (Fritillaria meleagris L., Liliaceae) is a spring-flowering, critically endangered plant in the Polish flora, red-listed in most of the European countries of its range. Based on indirect evidence, that is, body pollen loads, visitation frequency and seasonal abundance, it is estimated that its key pollinators are queen bumblebees, but, as shown in the literature, the largest Fritillaria pollen loads are carried by solitary bees. To study pollinator effectiveness for floral visitors to F. meleagris, we performed a garden experiment, where we analysed pollen deposition and assessed pollen removal per single flower-visit in the plant. Similarly to field conditions reported in the literature, our experimental plants were serviced by nectar-seeking bumblebee queens and two taxa of solitary bees, small pollen-collecting Andrena and large, nectar-seeking Anthophora males. When “quality” component was addressed, despite the character of visits, insects from all groups deposited more pollen than was found on unvisited flowers, but they did not differ significantly from each other in pollen deposition on virgin stigmas. We also found some differences in pollen removal both within- and among-visitor species and control flowers, unfortunately due to extremely high variation of the results they were all statistically insignificant. However, when “quantity” component of insect performance was concerned, we observed that over 81 % of visits were by bumblebees. Bombus queens stayed on flowers significantly less time than small Andrena individuals (13 % of recorded visits) and equally long as Anthophora males (only 6 % of visits). We conclude that although all the visitor groups can pollinate the flowers of F. meleagris, bumblebee queens indeed proved to be the most effective pollinators of the plant, when both quality and quantity components of pollination are concerned.

Highlights

Different floral visitors affect pollination of flowers in different ways depending on their relative size, visit frequency and behaviour. ‘‘The most effective pollinator’’ principle formulated by Stebbins (1970; p. 318) implies that floral characters should evolve to match ‘‘the most frequent and effective’’ visitor
Fritillary in our experimental array at the botanic gardens was pollinated by overwintered bumblebee queens and solitary bees, to those seen in field conditions (Hedstrom 1983; Zych and Stpiczynska 2012)
Sahli and Conner (2007) found a similar lack of effect of body size on removal, but significant differences between nectar and pollen foragers in a study on wild radish. Such differences were reported by Wilson and Thomson (1991) in a study of Impatiens capensis (Balsaminaceae), where nectar foraging Bombus removed relatively small amounts of pollen and deposited much of it compared to pollen foraging A. mellifera and solitary bees

Summary

Introduction

Different floral visitors affect pollination of flowers in different ways depending on their relative size, visit frequency and behaviour. ‘‘The most effective pollinator’’ principle formulated by Stebbins (1970; p. 318) implies that floral characters should evolve to match ‘‘the most frequent and effective’’ visitor. When we look at various metrics used to quantify pollinator performance (presented and/or reviewed in, e.g., Kearns and Inouye 1993; Dafni et al 2005; Fenster et al 2004; Ne’eman et al 2010), we may distinguish between a ‘‘quantitative’’ and ‘‘qualitative’’ component of animal activity, where quality determines animal’s ability to deliver pollen grains to conspecific stigmas, and quantity usually refers to the frequency of visits to a particular plant species (Herrera 1987; Olsen 1997) These two components of insect effectiveness (sensu Willmer 2011) are independent because rare visitors may carry more pollen than the common ones or vice versa The particular components of effectiveness of main floral visitors may be highly variable among years and/or sites (Ollerton 1996; Gomez and Zamora 1999; Lamborn and Ollerton 2000; Ivey et al 2003; Gibson et al 2006; Ollerton et al 2007; Davila and Wardle 2008; Lay et al 2011; Robertson and Leavitt 2011)

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