The paper 'The fragility of extreme specialisation: Passiflora mixta and its pollinating hummingbird Ensifera ensifera' by Annika Büchert Christensen of The Institute of Biological Science, University of Aarhus demonstrates P. mixta's total dependence on E. ensifera:- Abstract: Extreme specialisation between plants and their pollinators is expected to be very sensitive to habitat fragmentation, since the loss of one interactant inevitably will affect the other. In the present study, the effect of habitat fragmentation on the specialised interactions between the long-tubed flowers of Passiflora mixta and its extremely long-billed pollinator the Sword-billed hummingbird Ensifera ensifera was studied in natural forest and in open land. Pollen collection from skinned specimens of E. ensifera contained high levels of Passiflora pollen and indicated that this hummingbird is a frequent and important visitor of Passiflora. Low fruit set was observed in open land, where E. ensifera was lacking in both 1994 and 1995. Higher fruit set was found in the forest, where E. ensifera was a frequent visitor of P. mixta. Only the lack of E. ensifera in the open land could explain the reduced fruit set. This study may therefore represent an example of a vital breakdown of a specialised plant-pollinator interaction due to habitat fragmentation. We suggest that many endemic Passiflora species in the Andean highlands are threatened due to the disappearance of their pollinator. The study of pollination and seed set of these species would therefore be good indicators of "health of the community". Annika comments further 'I believe that the many of the species in the subgenus Tacsonia are dependent on Ensifera ensifera. E. ensifera vary a lot in bill length and Tacsonia species vary a lot in corolla tube length. It could be interesting to make a study of E. ensifera bill length and Tacsonia corolla tube length in all of the Andes. The decline in the number of E. ensifera would put a lot of pressure on Tacsonia species to evolve a shorter corolla tube (to be pollinated by shorter billed hummingbird species) or to become self pollinating.' I have recently received some wild collected seed (Colombia) of P. mixta with a smaller flower & shorter floral tube, so perhaps the plant is adapting to attract new pollinators as variations with slightly longer floral tubes may not be pollinated at lower altitudes. Tacsonia that can self pollinate however have established in New Zealand to the extent that they are a pest despite there being no hummingbirds. Probably some nectar loving local birds or insects are also pollinating them. | 
Ensifera ensifera & Tacsonia
