Pollen limitation and pollinator preferences in Scorzonera hispanica

Abstract

The plant life cycle is often affected by animal-plant interactions. In insect-pollinated plants, interaction with pollinators is very important. When pollen transfer due to a lower abundance of pollinators limits seed production, selection pressures on plant traits related to plant attraction to pollinators might occur, e.g. on flowering phenology, height or number of flowerheads. Landscape changes (e.g. habitat fragmentation or changed habitat conditions) may cause plant-pollinator systems to lose balance and consequently affect population dynamics of many plant species. We studied the relationship between measured plant traits, environmental variables and pollinator preferences in Scorzonera hispanica (Asteraceae), a rare perennial, allogamous herb of open grasslands. We estimated the pollen limitation by comparing seed set of supplemental-pollinated plants with that of open-pollinated ones. Pollinators selected plants based on position within the locality (isolated plants close to trees) rather than on their traits. In spite of a high proportion of undeveloped seeds on the plants, we demonstrated that they are not pollen limited. Instead, seed set and weight of seeds was correlated with plant size traits (height and flowerhead number), with larger plants producing more and larger seeds. This suggests that the studied plants are likely resource limited. Overall, the results suggest that pollinators are not a selection factor in this system, in contrast to studies on various plant species, including self-compatible species of the Asteraceae. The lack of any effect of pollinators in the system may be caused by a strong negative effect of ungulate herbivores, which could play a decisive role in functioning of the system.

Pollinator limitation on reproductive success in Iris tuberosa

“…This was unexpected, since this plant species is pollinated by many different species of insects, while it is widely assumed that specialized plants will be more prone to experiencing pollen limitation than generalized plants ( Knight et al 2005 ). These results contradict other studies ( Ehlers 1999 ; Červenková and Münzbergová 2013 ) but, on the contrary, are in agreement with many studies using similar experimental methods to detect pollen limitation in Rosaceae and Brassicaceae ( Pflugshaupt et al 2002 ; Sandring and Agren 2009 ). Moreover, these results confirm that pollen limitation is more common in self-incompatible species than in species that are self-compatible ( Mustajarvi et al 2001 ).…”

Vertical stratification of plant–pollinator interactions in a temperate grassland

“…Vertical position was thus the only apparent difference between the inflorescences. This is important because taller plants usually have higher percentage seed set even when they are hand-pollinated because they have more resources than shorter plants ( Andersson, 1996 ; Červenková & Münzbergová, 2014 ). Testing for pollinator-mediated selection on inflorescence height thus requires specific experimental designs and is not possible by simply comparing plants of different height.…”

“…Testing for pollinator-mediated selection on inflorescence height thus requires specific experimental designs and is not possible by simply comparing plants of different height. The most frequent approach is to compare selection coefficients for inflorescence height between open-pollinated and hand-pollinated plants ( Sletvold, Grindeland & Ågren, 2010 ; Červenková & Münzbergová, 2014 ; Jiang & Li, 2017 ; Trunschke, Sletvold & Ågren, 2017 ). We used an alternative approach, which allowed us to skip the hand-pollination treatment.…”

Contrasting effects of ploidy level on seed production in a diploid tetraploid system

“…Gomez 2003; Červenková and Münzbergová 2014; Schlinkert et al 2015). At the same time, however, these flower heads may also be more visible to herbivores and be subjected to higher seed losses (e.g.…”

“…Loranger et al 2012; Münzbergová and Skuhrovec 2013; Gross and Schiestl 2015; Schlinkert et al 2015; Smith et al 2015) to characteristics of plant surroundings, such as vegetation height or conspecific and heterospecific density and diversity (e.g. Weber and Kolb 2013; Burt et al 2014; Červenková and Münzbergová 2014; Hulber et al 2015; Kim and Underwood 2015) and to population characteristics, such as population size or density (e.g. Münzbergová 2006a; Sober et al 2009).…”