Yucca baccata cheats in its obligate pollination/seed predation mutualism w
ith yucca moths. Although all individuals use the pollination services of y
ucca moths, many individuals do not reciprocate in sustaining yucca moth la
rvae. Cheating is associated with the morphology of Y. baccata pistils. In
Y. baccata, the apex of the ovary contains only inviable ovules, and there
are two distinct flower types, one of which has twice as many potentially v
iable ovules as the other. Because yucca moths oviposit at the apex of Y. b
accata ovaries, larvae in flowers with few viable ovules fail to encounter
viable ovules and therefore perish. Inflorescences generally have just one
flower type, implying that some individuals cheat whereas others maintain t
he yucca moth population. Our most surprising observation, however, is that
although the proportion of cheaters should be low, over 70% of Y. baccata
individuals cheat. Me hypothesize that both density- and frequency-dependen
t processes maintain a balance of cheaters and noncheaters in this system.