Weather, Pollination and the Phenology of Geranium maculatum

Bertin, Robert I.; Sholes, Owen D. V.

doi:10.2307/2426435

Cited by 22 publications

(25 citation statements)

References 34 publications

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“…Our results are consistent with those of Herrera (1995b), who found that Hymenopterans preferred to forage in areas with high irradiance. Bertin and Sholes (1993) found that G. maculatum received less pollen as either the density of the tree canopy or cloud cover increased in a forest with no shrub layer, results consistent with shade as a mechanism causing reduced pollinator services to G. maculatum. Hymenopteran visitation is also influenced by air temperature, which was positively related to irradiance in a meadow habitat (Herrera 1995a).…”

Section: Impacts On Pollinator Servicesmentioning

confidence: 52%

“…It produces 2-30 large (2.5-4 cm wide) purple-pink flowers per plant. Hermaphroditic flowers are protandrous (Bertin and Sholes 1993), and pollinators are required for seed set to occur (Willson et al 1979); flowers are self-compatible and produce more seeds when fertilized by outcross pollen (Martin 1965). Visitors to G. maculatum are mainly solitary bees of the genera Andrena, Ceratina, Dialictus, Halictus, Nomada and Osmia (Robertson 1928;McCall and Primack 1987;Bertin and Sholes 1993) but also include Apis mellifera, Lepidopterans (Bertin and Sholes 1993) and syrphid flies (Agren and Willson 1991).…”

Section: Study Speciesmentioning

confidence: 99%

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Shading by invasive shrub reduces seed production and pollinator services in a native herb

2010

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Plant invasions disrupt native plant reproduction directly via competition for light and other resources and indirectly via competition for pollination. Furthermore, shading by an invasive plant may reduce pollinator visitation and therefore reproduction in native plants. Our study quantifies and identifies mechanisms of these direct and indirect effects of an invasive shrub on pollination and reproductive success of a native herb. We measured pollinator visitation rate, pollen deposition, and female reproductive success in potted arrays of native Geranium maculatum in deciduous forest plots invaded by the non-native shrub Lonicera maackii and in two removal treatments: removal of aboveground L. maackii biomass and removal of flowers. We compared fruit and seed production between open-pollinated and pollen-supplemented plants to test for pollen and light limitation of reproduction. Plots with L. maackii had significantly lower light, pollinator visitation rate, and conspecific pollen deposition to G. maculatum than biomass removal plots. Lonicera maackii flower removal did not increase pollinator visitation or pollen deposition compared to unmanipulated invaded plots, refuting the hypothesis of competition for pollinators. Thus, pollinator-mediated impacts of invasive plants are not limited to periods of co-flowering or pollinator sharing between potential competitors. Geranium maculatum plants produced significantly fewer seeds in plots containing L. maackii than in plant removal plots. Seed set was similar between pollen-supplemented and open-pollinated plants, but pollen-supplemented plants exhibited higher seed set in plant removal plots compared to invaded plots. Therefore, we conclude that the mechanism of impact of L. maackii on G. maculatum reproduction was increased understory shade.

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Section: Impacts On Pollinator Servicesmentioning

confidence: 52%

Section: Study Speciesmentioning

confidence: 99%

Shading by invasive shrub reduces seed production and pollinator services in a native herb

2010

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“…Each flower on a plant is a "trial" at capturing pollen, and counts of stigmatic pollen loads indicate wide variation in success (table 1 ; see also Koptur 1984;Garwood and Horvitz 1985;Cruzan et al 1988;Elam and Linhart 1988;Bertin and Sholes 1993). Given limited resources for making ovules and other floral parts, selection favoring efficient reproductive allocation, including ovule packaging that matches, in some way, the probable levels of pollen receipt and fertilization, would be expected.…”

Section: Pollen Receipt and Maximization Criterionmentioning

confidence: 99%

Ovule Packaging in Stochastic Pollination and Fertilization Environments

Burd

1995

Evolution

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Abstract.-The modular morphology of plants has important consequences for reproductive strategies. Ovules are packaged in discrete structures (flowers) that usually vary stochastically in pollen capture and ovule fertilization, because of the vagaries of pollen transfer by external agents. Different ovule packaging schemes may use limited reproductive resources more or less effectively, so that some number of ovules per flower may be optimal, given the prevailing probabilities of ovule fertilization. I derive a phenotypic model for ovule number per flower that maximizes the expected total ovule fertilizations on a plant when pollination and fertilization vary randomly among individual flowers. This model predicts that, except for small or inexpensive flowers, ovules should be "oversupplied" relative to the mean receipt of pollen tubes, so that pollen limitation of seed set should be common. Published data are congruent with this prediction. Additional hypotheses on the relation of ovule packaging to floral cost, plant size, and variance in pollen receipt are suggested by the model, but few data exist to evaluate these hypotheses.

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“…Plant reproduction and ®tness often depend on pollination, which can be in¯uenced by the local density of conspeci®c plants and¯owers (e.g., Feinsinger et al 1986Feinsinger et al , 1991Levin 1990;Kunin 1992), sex ratios and species composition in¯oral neighborhoods (e.g., Feinsinger et al 1986;Kunin 1993;Lalonde and Roitberg 1994;Cunningham 1995), climate (e.g., Murcia 1990;Bertin and Sholes 1993;Herrera 1995), as well as intrinsic dierences in¯oral attributes (e.g., Stanton 1987;Galen 1989;Campbell 1989;Real and Rathcke 1991;Cresswell and Robertson 1994). While many studies have examined each of these factors in isolation, few have looked at the interaction between dierent extrinsic or intrinsic¯oral variables.…”

Section: Introductionmentioning

confidence: 99%

Influence of local floral density and sex ratio on pollen receipt and seed output: empirical and experimental results in dichogamous Alstroemeria aurea (Alstroemeriaceae)

Aizen

1997

Oecologia

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Local density and sexual composition are two aspects of floral neighborhoods thought to influence pollination and seed output of recipient plants. I characterized the floral neighborhood of 436 flowering ramets of Alstroemeria aurea, a southern Andean perennial, distributed among three sites. On each ramet, I measured total pollen receipt and seed output. The long-lived, bumblebee-pollinated flowers of A. aurea are synchronously protandrous with a given ramet being either all male or all female and thus incapable of self or geitonogamous pollination at the ramet level. Even though each ramet changes sex over time, A. aurea forms floral neighborhoods that remain stable with respect to density and sex ratio during the span of a focal ramet female phase. Contrary to expectation, under field conditions neither local density nor sexual identity explained significant amounts of variation in pollen receipt. Density of neighboring flowering ramets marginally affected pollen receipt in two of the three populations but in opposite directions. Despite the absence of strong effects of neighborhood sexual composition on pollen receipt, the sexual identity of neighbors affected seed output which suggests effects on the quality of pollination due to changes in patterns of pollen flow. I also compared pollen loads on the stigmas of artificially isolated ramets (6 m) with those on experimental focal ramets surrounded by six close neighbors (20 cm) that were either all male or all female. Here, pollen receipt by focal ramets in all-male neighborhoods was 1.3 times greater than in isolated ramets, and 3.8 times greater than in ramets in all-female neighborhoods. In these artificial neighborhoods, stigmatic pollen deposition increased significantly over time. In nature, rates of bumblebee visits were higher in female-biased (early-flowering) than in male-biased (late-flowering) co-occurring floral patches. Thus, spatio-temporal shifts in visitation frequencies associated with the sexual composition of floral neighborhoods might compensate for spatial variability in pollen availability within populations and explain the discrepancies between empirical and experimental results.

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Weather, Pollination and the Phenology of Geranium maculatum

Cited by 22 publications

References 34 publications

Shading by invasive shrub reduces seed production and pollinator services in a native herb

Shading by invasive shrub reduces seed production and pollinator services in a native herb

Ovule Packaging in Stochastic Pollination and Fertilization Environments

Influence of local floral density and sex ratio on pollen receipt and seed output: empirical and experimental results in dichogamous Alstroemeria aurea (Alstroemeriaceae)

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