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ABSTRACT-Astrophytum asterias (star cactus) is an obligate outcrosser that does not reproduce vegetatively, so all reproduction is the result of inter-plant transfer of pollen by insects. By measuring seed set resulting from single pollinator visits, we evaluated effectiveness (mean seed set per visit) and importance of pollinator (effectiveness times frequency of visitation) of insects visiting flowers of A. asterias. Results indicate that the most common visitor, Macrotera lobata, is a relatively ineffective pollinator, while the less common Diadasia rinconis is the most effective and important pollinator. Two behavioral variables (duration of visit, whether or not visitors landed on the stigma) were assessed as possible predictors of fruit set. While duration of visit was not predictive of fruit set, there was a positive correlation between fruit set and the proportion of visits a visitor landed on the stigma when entering the flower.
RESUMEN-Astrophytum asterias (biznaga-algodoncillo de estrella) posee cruzamiento exo'geno obligado y no se reproduce por medios vegetales. Por lo tanto, toda su reproduccio'n es el resultado de polinizacio'n entrecruzada por medio de insectos. Midiendo el nu'mero de semillas producidas por visitas de un solo polinizador, evaluamos la eficacia (nu'mero promedio de semillas/visita) y la importancia (eficacia por frecuencia de visitas) de polinizadores insectos visitando flores de A. asterias. Los resultados indican que el visitante ma's comu'n, Macrotera lobata, es relativamente ineficaz como polinizador, mientras que el menos comu'n Diadasia rinconis es el ma's eficaz e importante de los polinizadores. Dos variables de comportamiento (duracio'n de visita, contacto con el estigma) fueron evaluadas como posibles prono' sticos de produccio'n de frutas. Mientras que la duracio'n de visita no se correlaciono' con produccio'n de frutas, hubo una correlacio'n positiva entre la produccio'n de frutas y la proporcio'n de visitas cuando un polinizador se poso' en el estigma al entrar en la flor.
In the past decade, it has become clear that effective management of populations of rare plants must include understanding communitylevel processes that affect these populations (Sipes and Tepedino, 1995; Corbet, 1997; Timmerman-Erskine and Boyd, 1999; Wall et al., 2003). Interactions between plants and their pollinators are of particular importance as many endangered plants are dependent on pollinators for reproduction and maintenance of viable populations (Nabhan and Flemming, 1993; Kearns and Inouye, 1997; Kearns et...