Are reward polymorphisms subject to frequency- and density-dependent selection? Evidence from a monoecious species pollinated by deceit

Authors

  • R. A. Castillo,

    1. Departamento de Ecología Evolutiva, Instituto de Ecología, UNAM, México
    2. Departamento de Investigaciones Científicas y Tecnológicas de la Universidad de Sonora, Hermosillo, Sonora, México
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  • C. Cordero,

    1. Departamento de Ecología Evolutiva, Instituto de Ecología, UNAM, México
    2. CEAMISH, Universidad Autónoma del Estado de Morelos, Cuernavaca, Morelos, México
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  • C. A. Domínguez

    1. Departamento de Ecología Evolutiva, Instituto de Ecología, UNAM, México
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 César A. Domínguez, Instituto de Ecología, UNAM, A.P. 70-275, Mexico D.F. 04510, Mexico. Tel.: 56 22 90 39; fax: 56 16 19 76; e-mail: tejada@servidor.unam.mx

Abstract

Abstract Most deceit-pollinated species involve floral dimorphisms characterized by the presence of rewarding male flowers and nonrewarding female flowers. It has been proposed that this polymorphism establishes the conditions for the action of frequency dependent selection (FDS). The tendency of foraging animals to aggregate in areas of high resource density suggests that pollination efficiency and fruit production may be positively influenced by flower density (density dependent selection, DDS). In this paper we offer a graphical model describing the effects of FDS and DDS on a monoecious species pollinated by deceit. We test the FDS and DDS assumptions and the predictions of the model using field observations and experimental populations of Begonia gracilis in which population sex ratio and flower density were controlled. We found a marked effect of both FDS and DDS on pollinator visitation, fruit-set, and on the probability of female flowers to setting fruits. We conclude that these two types of selection have had a strong influence on the evolution of deceit-pollinated species.

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