Sugar landscapes and pollinator‐mediated interactions in plant communities

Abstract

Pollinator‐mediated interactions between plants can play an important role for the dynamics of plant communities. Pollination services depend on the abundance and the foraging behaviour of pollinators, which in turn respond to the availability and distribution of floral resources (notably nectar sugar). However, it is still insufficiently understood how the ‘sugar landscapes’ provided by flowering plant communities shape pollinator‐mediated interactions between multiple plant species and across different spatial scales. A better understanding of pollinator‐mediated interactions requires an integrative approach that quantifies different aspects of sugar landscapes and investigates their relative importance for pollinator behaviour and plant reproductive success. In this study, we quantified such sugar landscapes from individual‐based maps of Protea shrub communities in the Cape Floristic Region, South Africa. The 27 study sites of 4 ha each jointly comprise 127 993 individuals of 19 species. We analysed how rates of visitation by key bird pollinators and the seed set of plants respond to different aspects of sugar landscapes: the distribution of nectar sugar amounts, as well as their quality, taxonomic purity and phenology. We found that pollinator visitation rates strongly depended on phenological variation of site‐scale sugar amounts. The seed set of focal plants increased with nectar sugar amounts of conspecific neighbours and with site‐scale sugar amounts. Seed set increased particularly strongly if site‐scale sugar amounts were provided by plants that offer less sugar per inflorescence. These combined effects of the amount, quality, purity and phenological variation of nectar sugar show that nectar sugar is a common interaction currency that determines how multiple plant species interact via shared pollinators. The responses of pollinator‐mediated interactions to different aspects of this interaction currency alter conditions for species coexistence in Protea communities and may cause community‐level Allee effects that promote extinction cascades.

Pollination outcomes reveal negative density‐dependence coupled with interspecific facilitation among plants

“…Although NDD may be perceived at the landscape‐level, flower abundance influences pollination outcomes at small spatial scales, that is, between neighbouring plants (Nottebrock et al ). Plants may exhibit negative or positive intraspecific responses (when high conspecific density attracts less or more pollinators, respectively, Totland ), interspecific facilitation (when plants of different species jointly attract more pollinators, Moeller ) and interspecific competition (when visitation rates are reduced by plants of other species, Mitchell et al ).…”

The potential indirect effects among plants via shared hummingbird pollinators are structured by phenotypic similarity

“…) or facilitation (Nottebrock et al. ). While the exact consequence of such indirect effects is sometimes hard to identify, the potential for such indirect effects will be dependent on the number of pollinators shared and on the contribution that each plant species makes to the diet of the pollinators of another plant.…”

“…Plant species are connected by shared pollinators in complex networks of ecological interactions, and hence can influence each other via indirect effects. Such effects may include competition for pollinator visits (Mitchell et al 2009), heterospecific pollen deposition (Arceo-G omez et al 2016) or facilitation (Nottebrock et al 2016). While the exact consequence of such indirect effects is sometimes hard to identify, the potential for such indirect effects will be dependent on the number of pollinators shared and on the contribution that each plant species makes to the diet of the pollinators of another plant.…”

Mapping floral resources for honey bees in New Zealand at the catchment scale

“…They can also form the basis for some further research to understand the importance of nectar supply for plant–pollinator interactions (Nottebrock et al. ) and weed reproduction (Butz Huryn and Moller ). The methodology is generic enough that it could be applied to other pollinators.…”

“…These maps will be useful to understand limiting factors in the landscape and better prepare beekeepers for hives wintering to reduce the need to use sugar supplements. They can also form the basis for some further research to understand the importance of nectar supply for plant-pollinator interactions (Nottebrock et al 2017) and weed reproduction (Butz Huryn and Moller 1995). The methodology is generic enough that it could be applied to other pollinators.…”