Effects of the availability of floral resources and neighboring plants on nectar robbery in a specialized pollination system

Many plants pollinated by nectar-foraging animals have to maintain a balance between legitimate visitor attraction strategies and mechanisms that minimize illegitimate visits. This study investigated how floral display and neighboring species composition influences nectar robbing in the tropical ornithophilous herb Heliconia spathocircinata. We tested the role of inflorescence display, flower abundance, and neighboring species in the reduction of nectar robbing in H. spathocircinata. Our results indicate that nectar robbing hummingbird activity was higher in moderately large inflorescence displays and that the frequency of nectar robbing in H. spathocircinata decreases with increased flower abundance and the presence of neighboring plant species. Neighboring non-ornithophilous plants decreased the frequency of nectar robbing in H. spathocircinata flowers to a greater extent than ornithophilous ones. These results suggest that nectar robbing hummingbirds are attracted to similar conditions that attract legitimate visitors, and that spatial aggregation and mixed-species displays may represent a mechanism to dilute nectar robbing effects at an individual level.

Nectar robbing in the trainbearers (Lesbia, Trochilidae)

Many flower visitors engage in floral larceny, a suite of so-called ’illegitimate’ visits in which foragers take nectar without providing pollination services. The data on prevalence of illegitimate visits among hummingbirds, as well as the total proportion of foraging and diet that such visits comprise is broadly lacking. Here, we report the occurrence of nectar larceny in the two currently recognized species of trainbearers and analyze the proportion of plant visits categorized by mode of interaction as: robbing, theft, and/or pollination. We augment our original field observations using a trove of data from citizen science databases. Although it is difficult to distinguish primary vs. secondary robbing and theft vs. pollination, we conservatively estimate that ca. 40% of the recorded nectar foraging visits involve nectar robbing. Males appear to engage in robbing marginally more than females, but further studies are necessary to confidently examine the multi-way interactions among sex, species, mode of visitation, and other factors. Our results also indicate that the suggested relationship between serrations on bill tomia and traits such as nectar robbing or territorial defense may be complicated. We discuss the significance of these findings in the context of recent developments in study of nectar foraging, larceny, and pollination from both avian and plant perspectives.

Nectar larceny in the trainbearers (Lesbia, Trochilidae)

ABSTRACTMany flower visitors engage in floral larceny, a suite of so-called ‘illegitimate’ visits in which foragers take nectar without providing pollination services. The data on prevalence of illegitimate visits among hummingbirds, as well as the total proportion of foraging and diet that such visits comprise is broadly lacking. Here, we report the occurrence of nectar larceny in both currently recognized species of trainbearers and analyze the proportion of plant visits categorized by mode of interaction as: primary robbing, secondary robbing, theft, and/or pollination. To the best of our knowledge, we provide the first published report identifying robbing in these species. We augment our original field observations using a trove of data from citizen science databases and literature. Although it is difficult to distinguish primary vs. secondary robbing and theft vs. pollination, we conservatively estimate that ca. 40% of the recorded nectar foraging visits involve nectar robbing. Males appear to engage in robbing marginally more than females, but further studies are necessary to confidently examine the multi-way interactions among sex, species, mode of visitation, and other factors. We discuss the significance of these findings in the context of recent developments in study of nectar foraging, larceny, and pollination from both avian and plant perspectives.

Pollination by nectar-foraging thynnine wasps in the endangered Caladenia arenaria and Caladenia concolor (Orchidaceae)

Prior to undertaking conservation translocations of plants with specialised pollination systems, it is important to ensure the presence of pollinators at recipient sites. Here, for two threatened species, Caladenia concolor Fitzg. and Caladenia arenaria Fitzg. (Orchidaceae), we determine (i) the pollination strategy used, (ii) which floral visitors are involved in pollination, and (iii) whether the pollinator species are present at potential translocation sites. For both orchid species, pollination was primarily achieved by nectar-foraging thynnine wasps, with a single species responsible for pollination in C. concolor, whereas C. arenaria utilised at least two species to achieve pollination. Both orchid species secreted meagre quantities of sucrose on the upper surface of the labellum. Visits to C. concolor occurred primarily in the late afternoon, with some wasps perching on the flowers overnight. Surveys revealed that pollinators were present at all extant populations and most potential translocation sites for both orchids. The specialisation on one pollinator species in C. concolor means that the distribution of the pollinator needs to be considered for conservation translocations. With C. arenaria, the risk of hybridisation with other Caladenia that are known to share one of its pollinator species needs to be taken into account when selecting translocation sites.