Conspecific and Heterospecific Plant Densities at Small-Scale Can Drive Plant-Pollinator Interactions

Abstract

Generalist pollinators are important in many habitats, but little research has been done on small-scale spatial variation in interactions between them and the plants that they visit. Here, using a spatially explicit approach, we examined whether multiple species of flowering plants occurring within a single meadow showed spatial structure in their generalist pollinator assemblages.We report the results for eight plant species for which at least 200 individual visits were recorded. We found that for all of these species, the proportions of their general pollinator assemblages accounted for by particular functional groups showed spatial heterogeneity at the scale of tens of metres. This heterogeneity was connected either with no or only subtle changes of vegetation and flowering species composition. In five of these species, differences in conspecific plant density influenced the pollinator communities (with greater dominance of main pollinators at low-conspecific plant densities). The density of heterospecific plant individuals influenced the pollinator spectrum in one case.Our results indicate that the picture of plant-pollinator interactions provided by averaging data within large plots may be misleading and that within-site spatial heterogeneity should be accounted for in terms of sampling effort allocation and analysis. Moreover, spatially structured plant-pollinator interactions may have important ecological and evolutionary consequences, especially for plant population biology.

Spatial variability in a plant–pollinator community across a continuous habitat: high heterogeneity in the face of apparent uniformity

“…Resource use rate was lowest in the resource-richest areas and highest in the poorest areas. Similarly, Janovský et al (2013) found a decrease in flower visitation rate with increased flower abundance and suggested that pollinator saturation may be a commoner phenomenon than previously thought. If flowers were sufficiently abundant, pollinators could locally find the necessary floral resources to satisfy their energy requirements.…”

“…Pollinators are highly mobile herbivores, and therefore an appropriate group of organisms to study local spatial distribution in relation to plant resource distribution. On the one hand, most pollinators are considered to be generalist and opportunistic in their foraging habits (Waser et al 1996), as exemplified by pollinator species foraging on different plant species in different floral contexts (Tylianakis et al 2007, Fründ et al 2010, Janovský et al 2013). On the other hand, even generalist pollinators such as polylectic bee species (those collecting pollen from various plant families) have been shown to have certain flower preferences, and may locally restrict their visits to one or a few plants (Westrich and Schmidt 1987, Petanidou et al 2008, Fründ et al 2010.…”

Experimental loss of generalist plants reveals alterations in plant-pollinator interactions and a constrained flexibility of foraging

“…That is, a given plant species had high visitation in one sampling transect and low in another transect, even on the same day. Although these patchy responses could be due to a local heterogeneity of abiotic factors 46 , it seems more likely that the set of neighbouring plant species and their relative abundances caused variations in competition and facilitation 44 . In other words, in one patch the facilitation might predominate, while competition might outweigh facilitation in another patch, thus resulting in very complex overall patterns 6 .…”

Immigrant inviability produces a strong barrier to gene flow between parapatric ecotypes of Senecio lautus

“…and consistency of pollinators in other studies of S. lautus (White 2008). While there is some evidence to suggest there may be strong effects of pollinator heterogeneity within environments (Janovsky et al 2013), we assume pollinator constancy here to maintain conservative estimates of reproductive barriers.…”