The relationships between floral traits and specificity of pollination systems in three Scandinavian plant communities

Abstract

The pollination syndrome hypothesis has provided a major conceptual framework for how plants and pollinators interact. However, the assumption of specialization in pollination systems and the reliability of floral traits in predicting the main pollinators have been questioned recently. In addition, the relationship between ecological and evolutionary specialization in pollination interactions is still poorly understood. We used data of 62 plant species from three communities across southern Norway to test: (1) the relationships between floral traits and the identity of pollinators, (2) the association between floral traits (evolutionary specialization) and ecological generalization, and (3) the consistency of both relationships across communities. Floral traits significantly affected the identity of pollinators in the three communities in a way consistent with the predictions derived from the pollination syndrome concept. However, hover flies and butterflies visited flowers with different shapes in different communities, which we mainly attribute to among-community variation in pollinator assemblages. Interestingly, ecological generalization depended more on the community-context (i.e. the plant and pollinator assemblages in the communities) than on specific floral traits. While open yellow and white flowers were the most generalist in two communities, they were the most specialist in the alpine community. Our results warn against the use of single measures of ecological generalization to question the pollination syndrome concept, and highlight the importance of community comparisons to assess the pollination syndromes, and to understand the relationships between ecological and evolutionary specialization in plant-pollinator interactions.

Floral colour versus phylogeny in structuring subalpine flowering communities

“…Other studies have found that white/yellow flowers are visited by fewer species (i.e. are more specialized), while purple flowers are more generalized in alpine environments (Lazaro et al 2008). With rare species being more purple/blue, our results may then indicate that these rare, purple-flowered species benefit from sharing generalist pollinators with common purple species, despite experiencing high amounts of heterospecific pollen (Sargent & Otto 2006;Spigler & Chang 2008).…”

“…Indeed, colour is among the most recognizable signals in the identification of 'pollination syndromes' relating to the perception and preference of pollinators (Faegri & van der Pijl 1979;Gumbert et al 1999;Fenster et al 2004;Lazaro et al 2008). For example, blue is typically associated with bee pollination, while red floral colour is related to hummingbird pollination (Faegri & van der Pijl 1979).…”

Floral symmetry: pollinator-mediated stabilizing selection on flower size in bilateral species

“…Floral symmetry was classified according to flower characteristics of each species. Species in the Asteraceae that contain both bilateral ray florets and radial disc florets have been assigned to radial species following Hegland & Totland (2005) and Lázaro et al's (2008) classifications. Following Dafni (1994) and Hegland & Totland (2005), the area in one plane of floral visual units of each species was calculated according to the shape of the flower.…”

“…We conducted a redundancy analysis with plant species as samples, percentage of the visits to a particular plant species attributed to each functional group as the response variable and floral symmetry (re-coded into dummy variables) as the explanatory variable. Total visits recorded for each plant species and plant species' abundance were entered as covariables to prevent the possible under-sample effects and the influence of composition of the visitor assemblage (Herrera, C. M. 2005;Lázaro et al 2008). Log ( y þ 1) was used to transform the response variables.…”

“…We initially performed a multivariate analysis to illustrate preferences of pollinator groups for different floral symmetries. Then, we quantified the level of pollination generalization or specialization (as a measure of pollinator diversity), given pollination systems ranging from specialized to generalized in species with both bilateral and radial flowers (Ollerton et al 2007;Lázaro et al 2008). The approach of characterizing ecological generalization in plant pollination systems (Sahli & Conner 2006) permits us to estimate the level of pollinator generalization using functional groups.…”