Temporal changes in the pollinator fauna of tristylous Pontederia cordata, an aquatic plant

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Abstract
Temporal changes in the composition of the pollinator fauna of the tristylous aquatic plant Pontederia cordata were documented during the flowering seasons of 1982 and 1983. A total of 18 species of insects, mainly bumblebees, and a single species of hummingbird were observed visiting flowers during the 2-month flowering period. The abundance of pollinators within each season varied greatly, with highest densities corresponding to peak flowering in both years. Although overall abundance was similar each year, the diversity of species was greater in 1983 because of the addition of short-tongued bumblebees and the longer residency periods of other species. It is suggested that low summer rainfall in 1983 decreased flowering levels in terrestrial plant communities of the region, resulting in several bee species shifting their feeding onto P. cordata. The study demonstrates that changes in the structure of a plant's pollinator fauna occur over time and that despite the possession of a specialized pollination mechanism, tristylous P. cordata is visited by a wide range of pollinator species.