PARENT SESSION
Organized Oral Session 3: Mutualists as parasites: How mutualistic are mutualists, and why?
Organizer(s): JR Powell, BE Wolfe, and JN Klironomos
Monday, August 8, 8:00 AM - 11:30 AM, Meeting Room 511a, Level 5, Palais des congrès de Montréal

Indirect costs of a mutualism: The most aggressive plant bodyguards also deter pollinators.

Ness, Joshua^{1, 2}, Bronstein, Judith¹, ¹ Dept Ecology and Evolutionary Biology, Tucson, Arizona, USA² Dept of Biology, Saratoga Springs, New York, USA

ABSTRACT- Plant defenses against herbivores may be costly if they exclude mutualists. Here, I test the hypothesis that aggressive ant bodyguards deter pollinators, and explore mechanisms by which Ferocactus wislizeni, an extrafloral nectary bearing cactus, limits conflicts between its pollinators and bodyguards. Flower visitation by ants and pollinating bees differed among plants tended by four different ant species. The ant species most rarely found in flowers showed the strongest aversion to F. wislizeni flower petals in laboratory assays, suggesting that those structures may include an ant-deterrent. Species-specific estimates of mean ant abundance within flowers and aggressiveness towards other arthropods were used to distinguish the relative threat of ant attack in flowers on plants tended by each ant species. Pollinator surveys in 2003 and 2004 demonstrated that bee visitation rates and the duration of flower occupation differed among plants with different ant associates, decreasing as the threat of ant attack increased. Flowers on plants tended by Solenopsis xyloni , the most protective ant bodyguard, were more dangerous than those on plants tended by three milder species, due to the greater aggressiveness and abundance of that ant within flowers. These flowers were visited by pollinators least frequently, and produced fruits with fewer, smaller seeds, relative to fruits from similar plants tended by three other ant species. As a result, the best bodyguard indirectly constrains plant reproduction. Conflicts between mutualistic guilds may be particularly common in generalized systems, where there is variation in partner quality and in the relative importance of protection and pollination mutualisms.

Key words: pollination, Solenopsis, ants, risk aversion