Cheaters among pollinators: Nectar robbing and thieving vary spatiotemporally with floral traits in Afrotropical forests
Abstract
Nectar robbers and thieves are common antagonists in plant-pollinator communities, where they deplete nectar without pollinating flowers, substantially affecting plant reproduction. Nevertheless, little is known about the relative abundance of such nectar exploiters in communities, even though spatiotemporal changes in the frequencies of antagonists and mutualists can exert opposing selection pressures on the traits of the interacting species.
Although these effects are highly dependent on the community context, interspecific interactions have almost exclusively been studied in interacting species pairs or single-plant studies. We hypothesized that flowers might experience a trade-off between filtering out robbers and thieves.
We used an extensive dataset of video-recorded flower-visitor interactions along a complete elevational gradient in wet and dry seasons on Mount Cameroon to assess spatiotemporal changes in robbing and thieving associated with several floral traits. Of the 14,391 recorded visits, similar to 4.3% were from robbers (mostly bees and birds) and similar to 2.1% were from thieves (mostly flies, bees, and moths).
Only 29 and 39 of the 194 studied plants were robbed and thieved, respectively. We found that specialized floral traits that prevented thieving (such as long floral tubes or spurs) made flowers susceptible to robbing, and vice versa.
Cheating behavior was most frequent at mid-elevations, with more frequent robbing during the wet season and thieving during the dry season. These trends were linked to the local floral trait composition and the associations of cheating groups with specific floral traits.
Our results suggest that the roles of antagonists and mutualists in shaping partner traits may vary across communities and that they deserve more attention in future studies of interspecific interactions.