Nectar Robbing Positively Influences the Reproductive Success of Tecomella undulata (Bignoniaceae)

Vineet Kumar Singh,Chandan Barman,Rajesh Tandon,Martin Heil

doi:10.1371/journal.pone.0102607

Abstract

The net consequence of nectar robbing on reproductive success of plants is usually negative and the positive effect is rarely produced. We evaluated the influence of nectar robbing on the behaviour of pollinators and the reproductive success of Tecomella undulata (Bignoniaceae) in a natural population. Experimental pollinations showed that the trees were strictly self-incompatible. The three types of floral colour morphs of the tree viz. red, orange and yellow, lacked compatibility barriers. The pollinators (Pycnonotus cafer and Pycnonotus leucotis) and the robber (Nectarinia asiatica) showed equal preference for all the morphs, as they visited each morph with nearly equal frequency and flower-handling time. The sunbirds caused up to 60% nectar robbing, mostly (99%) by piercing through the corolla tube. Although nectar is replenished at regular intervals, insufficient amount of nectar compelled the pollinators to visit additional trees in bloom. Data of manual nectar robbing from the entire tree showed that the pollinators covered lower number of flowers per tree (5 flowers/tree) and more trees per bout (7 trees/bout) than the unrobbed ones (19 flowers/tree and 2 trees bout). The robbed trees set a significantly greater amount of fruits than the unrobbed trees. However, the number of seeds in a fruit did not differ significantly. The study shows that plant-pollinator-robber interaction may benefit the self-incompatible plant species under conditions that increases the visits of pollinators among the compatible conspecifics in a population.

Highlights

Nectar robbing is an outcome of the ability of some floral foragers to steal nectar without effecting pollination [1,2]
We investigated the functional floral morphology, dynamics of nectar production and the mating system of the plant species, before integrating the interaction variables in the study
Mating system Experimental pollinations showed that fruit-set is realized only through cross-pollinations

Summary

Introduction

Nectar robbing is an outcome of the ability of some floral foragers to steal nectar without effecting pollination [1,2]. The phenomenon is prevalent in many taxonomically unrelated species of flowering plants, and those that hold concealed nectar in a tubular or spurred corolla [2,3,4]. The robbers may sometimes change their role to pollinators in the same or different plant species [4]. There are several instances where robbing produces partialnegative or weak-positive effects [8,9,10]. The net positive consequence becomes apparent when the fruit-set increases in response to robbing [11,12]. The phenomenon of nectar robbing is of common occurrence [3], the evidences for the types of interaction-frameworks and the key attributes that yield a range of consequences, have only recently begun to emerge [4,13,14]

Methods

Results

Conclusion