The nature of the mutualism between Agave palmeri and its bat pollinators (Leptonycteris curasoae and Choeronycteris mexicana) in southeastern Arizona

Although the relationship between the century plant Agave palmeri and nectar-feeding bats (in particular Leptonycteris curasoae and Choeronycteris mexicana) has been cited as an obligate mutualism, in the Chiricahua Mountains of southeastern Arizona there is considerable asynchrony between the blooming period of A. palmeri and the presence of nectar-feeding bats. I studied the use of alternative resources for reproduction by A. palmeri and for food by the bats. I carried out hand-pollination and pollinator exclusion experiments to determine the dependence of A. palmeri on bats. Although nectar-feeding bats increased seed and fruit production in A. pahneri, the plants were able to produce seeds through both diurnal pollination and, to a small extent, geitonogamous self-pollination, as well to propagate vegetatively. Sexual reproduction in this species may also be constrained by resource limitation. Although branches that were open to all visitors or only nocturnal visitors showed significantly higher fruit set (45.2% and 38.2% respectively) than those blocked from visitation (23.2%) or open only to diurnal visitors (17.5%), naturally pollinated plants achieved only a 26% fruit set over the course of the entire summer.;Dietary analysis and observation revealed that nectar-feeding bats readily used hummingbird feeders as a source of carbohydrates and that these feeders may greatly increase the energetic carrying capacity of the environment for these bats. I also found that L. curasoae included insects (primarily Coleoptera and Lepidoptera) in its diet, and these may provide a valuable source of protein in addition to pollen. Observations of the foraging behavior of L. curasoae failed to provide evidence for flock foraging, as has been previously described for this species. Although I found that both A. palmeri and its bat visitors may be able to rely on other resources for reproduction and survival, there is still considerable evidence of the importance of these partners to each other. Pollination of A. palmeri by nectar-feeding bats may provide qualitative advantages in addition to increased fruit and seed production, and A. palmeri pollen still appears to be the major source of protein for both L. curasoae and C. mexicana, even in the face of other energy sources.