Fragmentation and pollination crisis in the self-incompatible Iris Bismarckiana (IRIDACEAE), with implications for conservation

Recent evidence suggests that fragmentation effects on pollinators may drive plant species to extinction even if their immediate habitats are not affected. We hypothesize that species at high risk of suffering this "pollination crisis" are characterized by the following set of traits: self-incompatibility with synchronous flowering; reliance on a small number of pollinator species whose pollinators are specialists; and the existence of only a few, sparse populations. Iris bismarckiana fits this description perfectly. We studied two populations separated by recent urban development in order to (a) determine if the species is suffering a "pollination crisis", (b) assess which stage of the process limits reproductive success, and (c) evaluate artificial pollination as a viable conservation means for this species. We performed pollination experiments in two populations of I. bismarckiana. The overall natural fruit-set of open-pollinated inflorescences was around 13%, while supplementary cross-pollination by pollen from the same population substantially increased the fruit-set to 44%. An even greater fruit-set of 78% resulted from cross-pollination with pollen from the second population. Artificial cross-pollination also increased the number of seeds per capsule. Our results suggest that fragmentation may link the effects of inbreeding depression and pollinator activity to generate a "pollination crisis", expressed as significant reduction in sexual reproduction. We propose that supplementary cross-pollination, as well as transplanting of seeds, seedlings, and adult plants, may increase seed production and improve the survival chances of I. bismarckiana.