1996, pp 319-338

Reproductive Success and Gender Variation in Deceit-Pollinated Orchids

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In hermaphroditic plants differences in floral attractiveness to pollinators are expected to influence male and female reproductive success and thus functional gender (Nilsson, 1992). If reproductive success is limited by pollinator visitation, more attractive floral features are predicted to result in both more pollen exported and more seeds produced (Stanton and Preston, 1988). But what, more exactly, is the shape of the relationship between floral display and reproductive success in plants? This is clearly a critical issue that has to be clarified if floral evolution is to be understood. A greater individual display size in terms of number of flowers has been shown to result in an accelerating increase in the removal or receipt of pollen and thus probably male and/or female plant fitness via pollination (Schemske, 1980; Campbell, 1989a; see also Chapter 6). More commonly, however, a positive linear relationship between pollination success and floral display has been found (Willson and Price, 1977; Firmage and Cole, 1988; Campbell, 1989a; Broyles and Wyatt, 1990; Pleasants and Zimmerman, 1990). In some studies a decelerating increase in the visits by insects per flower, a measure that may be related to pollination success, has been reported (Galen and Newport, 1987; Andersson, 1988; Klinkhamer et al., 1989). An increase followed by a decrease in pollinator visitation with increasing inflorescence size has also been found (Bell, 1985; Pleasants and Zimmerman, 1990).