Avian nectar robbers of Passiflora mixta (Pasifloraceae): Do they have a positive effect on the plant?

Abstract

The effect of nectar robbing on plant reproduction may be negative, positive or neutral. The effect was evaluated on Passiflora mixta, an Andean high-mountain species that is pollinated by the Sword-billed Hummingbird (Ensifera ensifera). We determined: 1) the bird assemblage associated with P. mixta flowers, 2) the P. mixta flower nectar production pattern, 3) how nectar robbing affects fruit and seed production and 4) self-incompatibility in this species. Eight bird species were found associated with P. mixta flowers: five hummingbirds, two flower-piercers and one oriole. Experiments support the plant self-incompatibility. Nectar robbers do not harm the plant reproductive structure. The effect of nectar robbing appears to be positive, since robbers diminish the resource offered increasing pollen flow. In consequence, the effect of nectar robbers on P. mixta could be considered a relation of indirect mutualism