Truman P. YoungDepartment of Plant Sciences
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Tel. 530-754-9925
Fax: 530-752-4361
Email:tpyoung@ucdavis.edu
Todd M. Palmer, Maureen L. Stanton, and Truman P. Young.
Previous work has established that multiple mechanisms promote fine-scale coexistence between the acacia-ants, and that single trees often associate with a succession of ant species over their lifetimes. Our study system is an East African ant-plant mutualism in which four species of obligate acacia-ants compete for exclusive possession of individual trees of a single species of myrmecophyte, Acacia drepanolobium. Experimental manipulations and long-term surveys of host trees are used to document the costs and benefits to trees of associating with different ant species over the short-term, and to determine whether those fitness consequences depend on the pattern of transition between species of ant occupants.
Preliminary data indicate that the four ant species are likely to vary in services provided to their host tree (protection and soil nutrient enrichment), and in the degree to which they depend on commodities provided by the host (extrafloral nectar and swollen thorn domatia). Further experiments will test how variation in resources supplied by host trees to ants alters the behavior and performance of occupant colonies, as well as the rate at which transitions between occupant species occur. Finally, experimental manipulations of mammalian browsers will identify how spatial variation in herbivory in this ecosystem can change the frequencies and fitness consequences of alternative associations between ants and host trees.