Abstract
Fuchsia magellanica (Ongaraceae) is a plant with a traditionally ornithopholous pollination system, pollinated primarily by hummingbirds in its native range. As a naturalised alien plant in Ireland, F. magellanica is visited largely by bumblebees, with evidence for nectar robbing behaviour of the long-tubed flowers. We aimed to investigate nectar robbing behaviour of bumblebees on F. magellanica, and in particular whether floral and pollinator traits (size) determined likelihood of nectar robbing. While F. magellanica was visited by a number of bumblebee species, only two with shorter tongue lengths were observed to rob nectar from flowers. Although there was no observed relationship between intra-specific bee body size and nectar robbing behaviour, nectar robbing was observed most frequently in the site with the highest number of bees. Proportions of robbed flowers were low overall and varied between populations, but there was a significant relationship between flower size and whether it was nectar robbed with larger flowers robbed more often. Our work suggests that floral size determines whether a flower-visitor will choose to nectar rob or not in this system. Nectar robbing may also be related to bee density which could suggest this behaviour is driven by competition for resources, or that it is learnt by observing other bees.
Highlights
Faegri and Van der Pijl (1966, p. 68): "The distinction between simple theft and house-breaking exists in pollination ecology, too; thieves that cannot creep into the flower and steal nectar that way, may bite a hole through the perianth and get at it from the outside"Plants and the pollinators that visit them have co-evolved over long time periods (Ollerton 2017), resulting in some examples of extreme specialisation between both groups (e.g. Arditti et al 2012; Weinstein & Graham 2017)
B. hortorum was the largest of the observed bees which we know from the literature has the longest tongue (Goulson & Darvill 2004), and was followed in tongue length by B. lucorum agg. and B. pascuorum
Bumblebee species (B. lucorum agg and B. pascuorum), and not the longer tongued B. hortorum. This is consistent with the existing literature; a range of studies have shown that Hymenoptera, and in particular bees, are the most common primary robbers and commonly use Fuchsia magellanica is a naturalized, alien plant in Ireland. It has a classical ornithophilous pollination system and is visited primarily by hummingbirds in its native range, we have shown that in its naturalized range in Ireland it is visited mainly by bumblebees who use it as a forage resource through both legitimate and robbing visits
Summary
Faegri and Van der Pijl (1966, p. 68): "The distinction between simple theft and house-breaking exists in pollination ecology, too; thieves that cannot creep into the flower and steal nectar that way, may bite a hole through the perianth and get at it from the outside"Plants and the pollinators that visit them have co-evolved over long time periods (Ollerton 2017), resulting in some examples of extreme specialisation between both groups (e.g. Arditti et al 2012; Weinstein & Graham 2017). While nectar robbing can happen in various ways, the majority occurs when a flower visitor makes a hole in the perianth of a flowers to access nectar without “legitimately” visiting the flower (Inouye 1980). Primary nectar robbers are visitors that make the robbing hole themselves, whereas secondary robbers are those that use pre-existing holes (Inouye 1980) Evidence suggests that both plant and flowervisitor traits could play a role in the likelihood of nectar robbing occurrence, the morphological fit between flower and visitor. Those with long flowers and abundant nectar are more likely to be robbed (Rojas-Nossa et al 2016).
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