Effects of nectar-robbing on plant reproduction and evolution

The relationship between plant and pollinator is considered as the mutualism because plant benefits from the pollinator’s transport of male gametes and pollinator benefits from plant’s reward.Nectar robbers are frequently described as cheaters in the plant-pollinator mutualism,because it is assumed that they obtain a reward(nectar)without providing a service(pollination).Nectar robbers are birds,insects,or other flower visitors that remove nectar from flowers through a hole pierced or bitten in the corolla.Nectar robbing repre-sents a complex relationship between animals and plants.Whether plants benefit from the relationship is always a con-troversial issue in earlier studies.This paper is a review of the recent literatures on nectar robbing and attempts to acquire an expanded understanding of the ecological and evolutionary roles that robbers play.Understanding the effects of nectar robbers on the plants that they visited and other flower visi-tors is especially important when one considers the high rates of robbing that a plant population may experience and the high percentage of all flower visitors that nectar robbers make to some species.There are two standpoints in explaining why animals forage on flowers and steal nectar in an illegitimate behavior.One is that animals can only get food in illegitimate way because of the mismatch of the morphologies of animals’mouthparts and floral structure.The other point of view argues that nectar robbing is a relatively more efficient,thus more energy-saving way for animals to get nectar from flowers.This is probably associated with the difficulty of changing attitudes that have been held for a long time.In the case of positive effect,the bodies of nectar robbers frequently touch the sex organs of plants during their visiting to the flowers and causing pollination.The neutral effect,nectar robbers’behavior may destruct the corollas of flowers,but they neither touch the sex organs nor destroy the ovules.Their behavior does not affect the fruit sets or seed sets of the hosting plant.Besides the direct impacts on plants,nectar robbers may also have an indirect effect on the behavior of the legitimate pollinators.Under some circumstances,the change in pollinator behavior could result in improved repro-ductive fitness of plants through increased pollen flow and out-crossing.

The flowerpiercers interactions with a community of high Andean plants

Background:Flowerpiercers(Diglossa)are traditionally considered as“parasites”of the pollination processes,as they can access the nectar without entering in contact with the reproductive structures of the plants.Nevertheless,the effect of flowerpiercers seems to vary according to their behavior and the flower’s traits.So,in this work,we aimed to explore the floral characteristics that may determine the susceptibility to robbing and pollen transport by flowerpierc-ers.Also,we identified the potential types of interactions and studied interaction network properties.Methods:We collected the information of 16 ornithophilic plants regarding their floral traits and robbing frequency.Also,we captured 4 species of flowerpiercers and evaluated pollen transport(frequency and loads).We tested the correlation between floral traits,robbing frequency,and pollen transportation.Later,we used these variables in a cluster and principal component analyses to identify the potential types of interactions.Finally,we analyzed and com-pared the structure of the plants-flowerpiercers interaction network.Results:Nectar production significantly influenced both nectar robbing and pollen transportation.While the corolla length was only correlated to the robbing susceptibility.Also,we found that particular flowerpiercers species trans-ported higher loads of some plant pollen,which can be related to the differences in behavior and morphometric traits.We proposed the classification of five different types of plant-flowerpiercer interactions,that showed differ-ent potential mutualist or antagonist relations based on the affectation of nectar robbing and the service of pollen transportation.The interaction networks consisted of 49 links,with 2.4 links per species,and presented indicators of a medium to high resilience,stability,and resistance(nestedness,connectance,and robustness).Also,the network presented medium to low specialization and substantial niche overlap.Conclusions:The ecological role of the flowerpiercers goes beyond its classic assignation as“parasites”as they can actively transport pollen of several Andean plants,affecting its evolutionary history and the stability of the systems.