Effectiveness of ants as pollinators of Lobularia maritima: effects on main sequential fitness components of the host plant

The effectiveness of ants as pollinators of Lobularia maritima (Cruciferae) was experimentally analyzed by assessing (1) their quantitative importance at flowers; (2) their effect on host plant seed production; (3) their effe ct on the performance of host plant progeny, estimated as seed germination, seedling emergence, seedling survival to flowering, and (4) the overall ef fect of ants on a cumulative, more realistic measure of plant fitness relat ed to the recruitment probability. flowers of L. maritima were visited duri ng the 2 years of study (1996 and 1997) by more than 50 pollinator species belonging to about 30 families of disparate taxonomic affiliation, notably ants and flies. There was significant seasonal variability in insect abunda nce and type. Ants, especially Camponotus micans (Formicidae), visited the flowers of L. maritima in summer, representing 81.2% of the visits during t his season. This ant species acted as a pollinator of L, maritima, with flo wers visited exclusively by ants producing significantly more seeds than fl owers from which all pollinators were excluded, whereas flowers visited by only winged insects did not differ from self-pollination. Ant-pollinated fl owers produced seeds with a germination rate comparable to the other treatm ents. Moreover, seedlings from these seeds emerged as fast, and survived at the same rate as controls. Consequently, both ants and winged insects had similar overall effects on host plant recruitment probability (0.6 and 0.7% of initial ovules produced flowering offspring, respectively), a result si milar to that of open-pollinated flowers (1.0%). This study demonstrated th at the overall effectiveness of the ant C. micans as a summer pollinator of L. maritima was as high as that of other winged insects, contributing not only to the seed production of this crucifer but also to the recruitment of new flowering offspring.