Pollinator Limitation in the Facultatively Autogamous Annual, Lupinus Nanus (Leguminosae)

Abstract

The importance of pollinator visitation for determining both maternal reproductive success and outcrossing rates was investigated in the facultatively autogamous annual, Lupinus nanus. Sixty plants in each of two adjacent sites were assigned to either a pollinator‐exclusion, pollen‐augmentation, or open‐pollinated (control) treatment. Flower, fruit, and seed production were recorded for each plant, and outcrossing rates were determined for plants in all three treatments at each site. Pollinator‐exclusion reduced the reproductive success of plants at Site 1, but had no effect on reproduction for plants at Site 2. Pollen‐augmentation increased fruit production by 22% and seed production by 45% at Site 2, but had no effect on reproduction for plants at Site 1. Plants in the open‐pollinated, control treatment outcrossed at intermediate rates at both sites, with plants at Site 2 (outcrossing rate, t = 0.66) outcrossing at a significantly higher rate than plants at Site 1 (t = 0.40). The pollen‐augmentation treatment increased the outcrossing rate for plants at both sites (Site 1, t = 0.72; Site 2, t = 0.78). These results indicate that pollinator availability can limit maternal reproductive success for this facultatively autogamous plant species. Additionally, the intermediate outcrossing rates observed in nature for this species are not a consequence of plant characters alone, but instead result from plant characters combined with the local pollination ecology.

Floral stages, ovule development, and ovule and fruit success in Iris tenax, focusing on var. gormanii, a taxon with low seed set

“…Others have reported lowered fruit (papers reviewed in Bierzychudek, 1981;Karoly, 1992;Burd, 1994;Irwin, 2000) and seed production (Snow, 1982;Burd, 1994;Irwin, 2000) due to pollinator limitation. gormanii.…”

Pollen Quantity and Quality as Explanations for Low Seed Set in Small Populations Exemplified by Eupatorium (Asteraceae)

“…Consequences of limited pollen quantity (besides limited seed set) are a decrease in the quality of seed (lack of competition among pollen donors) or an increase in self-pollination (Bertin, 1990;Karoly, 1992;Richardson and Stephenson, 1992). Self-incompatible species receiving mostly self pollen will have reduced seed set due to either interference by self pollen or reception of inadequate compatible pollen (Silander and Primack, 1978;Garwood and Horvitz, 1985;Galen, Gregory, and Galloway, 1989;Whisler and Snow, 1992;Broyles and Wyatt, 1993).…”

Experimental Demonstration of an Allee Effect in American Ginseng

“…The species most vulnerable to population size effects are likely to be obligate outcrossers that have been reduced in population size by whatever cause (Huenneke 1991). Nevertheless, even plants capable of selfing can be pollinator-limited if (1) selfing effectiveness is reduced by lower pollinator activity or lower pollen transfer rate (Karoly 1992;Lloyd & Schoen 1992), (2) enhancement of outcrossing increases seed set while selfing remains the same (Travis 1984), or (3) there is a genetic load (i.e., reduced fitness) associated with selfing (Darwin 1876;Schoen 1983;Charlesworth 1989).…”