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Pollen Receipt (pollen + receipt)

Distribution by Scientific Domains

Life Sciences	100%

Selected Abstracts

The aerodynamics and efficiency of wind pollination in grasses

FUNCTIONAL ECOLOGY, Issue 4 2010
James E. Cresswell
Summary 1.,Under natural selection for sexual success, the reproductive organs of plants should evolve to become highly effective pollen receptors. Among wind-pollinated plants, larger reproductive structures appear counter-adapted to accumulate pollen by impaction on their windward surfaces, because airborne particles are less able to penetrate the thicker boundary layer of larger targets. Therefore, it has been proposed that wind-pollinated plants with pollen receptors on relatively large structures, like some grasses (family Poaceae), are architecturally adapted to create downstream vortices in which airborne pollen recirculates before accumulating on leeward surfaces. From this basis, the striking diversity among the grasses in the architecture of their flowering stems has been attributed in part to the existence of these contrasting mechanisms for effecting pollen receipt, namely impact collection and recirculatory collection. 2.,We investigated the relative importance of impact and recirculatory collection in grasses by analysing a model system in silico using Computational Fluid Dynamics and by conducting in vivo experiments, both in a wind tunnel and outdoors, using two grass species with compact inflorescences, Alopecurus pratensis and Anthoxanthum odoratum. 3.,Irrespective of the experimental approach, we found that although pollen recirculated in the leeward eddies of inflorescences, over 95% of the accumulated pollen was collected by windward surfaces. 4.,In A. pratensis, the collection efficiency (proportion of oncoming pollen collected) was between 5% and 20%, depending on wind speed in the range 0·5,1·9 m s,1 and these levels conform to those predicted by a mechanistic model of impact collection. 5.,Our results demonstrate that grass species with larger inflorescences are, like those with smaller inflorescences, primarily impact collectors of airborne pollen, which suggests that dissimilar reproductive morphology among species cannot be attributed to differentiation in the mode of pollen capture and, instead, requires reference to other factors, such as the need to produce, protect and disperse seeds of different sizes in different environments. [source]

Reproductive interactions mediated by flowering overlap in a temperate hummingbird,plant assemblage

OIKOS, Issue 4 2010
Marcelo A. Aizen
Pollinator-mediated competition through shared pollinators can lead to segregated flowering phenologies, but empirical evidence for the process responsible for this flowering pattern is sparse. During two flowering seasons, we examined whether increasing overlap in flowering phenology decreased conspecific pollination, increased heterospecific pollination, and depressed seed output in the seven species composing a hummingbird,plant assemblage from the temperate forest of southern South America. Overall trends were summarized using meta-analysis. Despite prevailing negative associations, relations between phenological overlap and conspecific pollen receipt varied extensively among species and between years. Heterospecific pollen receipt was low and presumably of limited biological significance. However, our results supported the hypothesis that concurrent flowering promotes interspecific pollen transfer, after accounting for changes in the abundance of conspecific flowers. Seed output was consistently reduced during maximum phenological overlap during the first flowering season because of limited fruit set. Responses varied more during the second year, despite an overall negative trend among species. Relations between estimated effects of phenological overlap on pollination and seed output, however, provided mixed evidence that conspecific pollen loss during pollinator visits to foreign flowers increases pollen limitation. By flowering together, different plant species might benefit each other's pollination by increasing hummingbird recruitment at the landscape level. Nevertheless, our results are mostly consistent with the hypothesis of pollinator-mediated competition shaping the segregated flowering pattern reported previously for this temperate plant assemblage. The mechanisms likely involve effects on male function, whereby pollen-transport loss during heterospecific flower visits limit pollen export, and more variable effects on female function through pollen limitation. [source]

Do pollen carryover and pollinator constancy mitigate effects of competition for pollination?

OIKOS, Issue 7 2009
Benjamin R. Montgomery
Pollinator constancy and pollen carryover are both thought to mitigate competitive effects that result when shared pollinators cause loss of pollen to heterospecific flowers. I present analytical and simulation models to investigate how pollinator constancy and pollen carryover interact with each other and with the relationship between pollen receipt and seed set to determine pollination success in competitive environments. With inconstant pollinators, increased pollen carryover reduces variance in pollen receipt without affecting average pollen receipt. Consequently, for flowers requiring at least a threshold quantity of pollen for success, rare flowers with inconstant pollinators benefit from reduced carryover, especially for high pollen receipt thresholds, whereas common flowers benefit from increased carryover, especially for low receipt thresholds. Pollinator constancy is predicted to increase pollen receipt, especially if pollen carryover rates are low. As a result, increased pollinator constancy reduces the range of pollen receipt thresholds for which carryover is beneficial. Similarly, for flowers whose pollination success is a convex function of pollen receipt, carryover is expected to increase fecundity if pollinators are inconstant, but with even a low degree of pollinator constancy, carryover reduces fecundity. These results predict that rare plants with many ovules per flower benefit from dispersing aggregations of pollen, especially if their pollinators exhibit constancy, whereas plants with inconstant pollinators and low thresholds of pollen receipt benefit from pollen grains dispersing individually to increase the number of flowers reached by the pollen. [source]