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In the last decade, an increasing number of studies have suggested that males and females of dioecious plants may be differentially affected by competition, herbivory, and parasitism. In dioecious plant species, there is a fundamental sexual difference in patterns of reproductive allocation. Males may allocate more resources to reproduction than females during flowering, but total reproductive allocation is typically greater in females than in males (Chap. 6). These sexual differences in schedules of reproductive allocation have in several species been found to be associated with differences in vegetative phenology, rate of growth, morphology, and chemical composition (Lloyd and Webb 1977; Chaps. 6 and 7), which are characters that are likely to affect competitive ability and interactions with herbivores and parasites (e.g., Crawley 1983; Keddy 1989; Marquis 1992; Dix and Webster 1995).