Magnitude Of Pollen Limitation Research Articles

Pollinator dependence but no pollen limitation for eight plants occurring north of the Arctic Circle.

Effective interactions between plants and pollinators are essential for the reproduction of plant species. Pollinator exclusion experiments and pollen supplementation experiments quantify the degree to which plants depend on animal pollinators and the degree to which plant reproduction is pollen limited. Pollen supplementation experiments have been conducted across the globe, but are rare in high latitude regions. To fill this knowledge gap, we experimentally investigated the dependence on animal pollinators and magnitude of pollen limitation in eight plant species north of the Arctic Circle in Lapland, Finland. Our findings show that all plant species were pollinator dependent, but not pollen limited. We discuss several mechanisms that might buffer our focal plants from pollen limitation, including plant and pollinator generalization, and attractive plant traits. Our results demonstrate that many plant species north of the Arctic Circle are currently receiving adequate pollinator service and provide a baseline for future comparisons of pollinator dependence and pollen limitation in the Arctic across space and time.

Pollen limitation and seed set associated with year-to-year variation in flowering of Gmelina arborea in a natural tropical forest

The year-to-year variations in flowering, pollen and fruit production in ten Gmelina arborea individuals in a natural forest were observed over a period of five years, 2009−2013, and pollinator visits were observed closely over two years, 2011 and 2012. A pollen supplementation experiment was also undertaken in two years (2011 and 2012) of contrasting flowering levels. Considerable year-to-year variations were observed in flower, pollen and fruit production. The observed variation represented a normal sequence of good-year and poor-year cycling which is most parsimoniously attributed to resource allocation. The average level of pollen production per individual tree in good flowering years oscillated between 6.6 and 9.62 × 108, which in the poor flowering years was between 1.92 and 3.07 × 108. The magnitude of pollen limitation across years was highly significant (p < 0.0001). Fruit set through supplemental pollination was 73% and 96% greater than that of the open-pollinated branches in the year 2011 and 2012, respectively. Pollen limitation, irrespective of the arrival of outcross pollen, can reduce annual seed set in predominantly bee-pollinated trees. However, various other factors may cause flower abortion in addition to pollen limitation. The results of this study would be very valuable to the seed orchard managers and the silviculturists to manage the seed production areas (SPAs) of G. arborea. The study ultimately recommends supplemental pollination in seed orchards of G. arborea for better genetic gain and good seed yield.

Pollination Ecology and Morphology of Venus Flytrap in Sites of Varying Time Since Last Fire

Management of natural habitats is an important strategy for rare plant conservation. One common tool for managing natural habitats is the use of controlled fire. Rare plants in fire-dependent ecosystems often rely on frequent fires to increase nutrient availability, initiate germination, and limit cover from light competitors. Fire can also alter arthropod communities, including the pollinator communities upon which many flowering plants rely for sexual reproduction. However, it remains unclear how fire affects the pollination ecology of rare plants in fire-dependent ecosystems. Here we studied sites of varying burn history to examine the role of time since last fire on the morphology, flower visitor community, and degree of pollen limitation of seed production of Venus flytrap (Dionaea muscipula). The area occupied by blooming D. muscipula and number of traps per individual decreased with increasing time since burn. Though flower visitor richness and evenness were highest in sites of intermediate time post-burn, we found no differences in the composition of the flower visitor community in sites of different burn histories. Hand-pollinated flowers produced 8.3% more seeds per fruit than open-pollinated flowers, indicating that D. muscipula was pollen-limited, but burn history did not affect the magnitude of pollen limitation. Though we found no clear effect of burn history on the pollination ecology of D. muscipula, differences in blooming area and trap number suggest that burn history influences its distribution and growth, and affirms the benefits of frequent fires to its persistence.

Self‐ and intra‐morph incompatibility and selection analysis of an inconspicuous distylous herb growing on the Tibetan plateau (Primula tibetica)

There is discussion over whether pollen limitation exerts selection on floral traits to increase floral display or selects for traits that promote autonomous self‐fertilization. Some studies have indicated that pollen limitation does not mediate selection on traits associated with either pollinator attraction or self‐fertilization. Primula tibetica is an inconspicuous cross‐fertilized plant that may suffer from pollen limitation. We conducted a selection analysis on P. tibetica to investigate whether pollen limitation results in selection for an increased floral display in case the evolution of autonomous self‐fertilization has been difficult for this plant. The self‐ and intra‐morph incompatibility features, the capacity for autonomous self‐fertilization, and the magnitude of pollen limitation were examined through hand‐pollination experiments. In 2016, we applied selection analysis on the flowering time, corolla width, stalk height, flower tube length, and flower number in P. tibetica by tagging 76 open‐pollinated plants and 37 hand‐pollinated plants in the field. Our results demonstrated that P. tibetica was strictly self‐ and intra‐morph incompatible. Moreover, the study population underwent severe pollen limitation during the 2016 flowering season. The selection gradients were found to be significantly positive for flowering time, flower number, and corolla width, and marginally significant for the stalk height. Pollinator‐mediated selection was found to be significant on the flower number and corolla width, and marginally significant on stalk height. Our results indicate that the increased floral display may be a vital strategy for small distylous species that have faced difficulty in evolving autonomous self‐fertilization.

Floral and mating system divergence in secondary sympatry: testing an alternative hypothesis to reinforcement in Clarkia.

Reproductive character displacement (RCD) is often an important signature of reinforcement when partially cross-compatible taxa meet in secondary sympatry. In this study, floral evolution is examined during the Holocene range expansion of Clarkia xantiana subsp. parviflora from eastern Pleistocene refugia to a western zone of sympatry with its sister taxon, subsp. xantiana. Floral divergence between the two taxa is greater in sympatry than allopatry. The goal was to test an alternative hypothesis to reinforcement - that floral divergence of sympatric genotypes is simply a by-product of adaptation to pollination environments that differ between the allopatric and sympatric portions of the subspecies' range. Floral trait data from two common garden studies were used to examine floral divergence between sympatric and allopatric regions and among phylogeographically defined lineages. In natural populations of C. x. parviflora, the magnitude of pollen limitation and reproductive assurance were quantified across its west-to-east range. Potted sympatric and allopatric genotypes were also reciprocally translocated between geographical regions to distinguish between the effects of floral phenotype versus contrasting pollinator environments on reproductive ecology. Sympatric populations are considerably smaller flowered with reduced herkogamy. Pollen limitation and the reproductive assurance value of selfing are greater in sympatric than in allopatric populations. Most significantly, reciprocal translocation experiments showed these differences in reproductive ecology cannot be attributed to contrasting pollinator environments between the sympatric and allopatric regions, but instead reflect the effects of flower size on pollinator attraction. Floral evolution occurred during the westward range expansion of parviflora, particularly in the zone of sympatry with xantiana. No evidence was found that strongly reduced flower size in sympatric parviflora (and RCD between parviflora and xantiana) is due to adaptation to limited pollinator availability. Rather, floral divergence appears to have been driven by other factors, such as interactions with congenerics in secondary sympatry.

Is reproduction of endemic plant species particularly pollen limited in biodiversity hotspots?

Current evidence suggests that plants in biodiversity hotspots suff er more from pollen limitation of reproduction than those in lower diversity regions, primarily due to the response of self-incompatible species. Species in biodiversity hotspots may thus be more at risk of limited reproduction and subsequent population decline. Should these species have restricted ranges (i.e. be endemics to a certain region), pollen limitation within highly diverse regions may pose an important threat to global plant biodiversity. We further dissect the global pattern by exploring whether pollen limitation of range-restricted (endemic) species is distinctive and/or relates diff erently to species diversity than that of widespread (non-endemic) species. To provide a preliminary test of this prediction we conducted both cross-species and comparative phylogenetic meta-analyses to determine the eff ect of endemism on the magnitude of pollen limitation and its relationship with regional species richness. Our data set included 287 plant species belonging to 78 families distributed world-wide. Our results revealed that endemism and self-compatibility contribute to the global association between pollen limitation and species richness. Self-incompatible species were more pollen limited than self-compatible ones, and the PICs analysis indicated that transitions to endemism were associated with transitions to self-compatibility. Th e relationship between pollen limitation and species richness was signifi cant only for the self-incompatible species, and was monotonically increasing in non-endemic species but accelerating in the endemic species. Th us, self-incompatible endemic species from biodiversity hotspots are at the greatest risk of pollination failure, a previously unknown aspect suggesting this group of species as a top priority for future development of conservation strategies. In contrast, reproduction of self-compatible species appears to be unrelated to plant diversity, although we caution that current data do not account for the reproductive limitation due to the quality of pollen received. Understanding the mechanisms underlying these patterns requires further investigation into plant–plant pollinator mediated interactions and the dynamics of pollen transfer in communities diff ering in species diversity.

Pollen Limitation and Local Habitat‐Dependent Pollinator Interactions in the Invasive Shrub Lonicera maackii

Many nonnative plants require pollinators to produce the seed needed to establish beyond their native range. Local variation in pollination can cause variation in mating patterns, reproductive output, genetic diversity, and selection, which can influence invasion dynamics. We quantified pollinator visitation, pollen deposition, and pollen limitation of reproduction in the invasive shrub Lonicera maackii in adjacent forest edge and forest interior habitats. Flowers in edge habitats received as many or more pollinator visits than those in interior habitats, resulting in twofold greater pollen deposition and nearly twice as many seeds produced per flower. Supplemental pollination increased seed production over open pollination by 37%–145% in both edge and interior habitats. Edge flowers produced more seed than interior flowers. Despite greater pollen deposition in edge habitats, the magnitude of pollen limitation was similar to interior plants. Thus, different mechanisms of pollen limitation characterize these habitats. Pollen receipt and other resources limited reproduction of interior plants, which were located in a shady environment. Pollen quality likely limited reproduction of edge plants, because pollinators visited more flowers per plant and likely delivered more geitonogamous pollen in this habitat than in the interior. Therefore, local variation in abiotic conditions influenced reproduction in this invasive plant, both directly and indirectly via pollinators.

Is the magnitude of pollen limitation in a plant community affected by pollinator visitation and plant species specialisation levels?

Pollen limitation on a plant community level has received little attention, although it might show which pollination‐related traits may cause pollen limitation to vary among species. To address several central questions in plant reproductive biology, we investigated pollen limitation in 11 plant species, including visitation and specialisation levels of all species. The female reproductive success of most species within the studied plant community was not pollen limited, but a general tradeoff between seed production and seed weight occurred as a response to supplemental pollination. In contrast to general notion, we did not find that less visited species were most pollen limited. Instead, it appears that species with high visitation rates were most pollen limited. Our study provided conflicting evidence to whether specialisation levels may affect the degree of pollen limitation within the study community. We discuss these findings in the context of recent reviews on the occurrence, causes and consequences of pollen limitation in plants. In particular, we propose that, although pollen limitation is an important phenomenon, 1) the majority of species within a plant community may not experience pollen limitation at a given moment, 2) that common notions of which plant species should experience pollen limited reproductive success do not hold true in the studied plant community, and 3) that offspring quality is as likely affected by surplus pollen loads as is the number of offspring.

Is the magnitude of pollen limitation in a plant community affected by pollinator visitation and plant species specialisation levels?

Is the magnitude of pollen limitation in a plant community affected by pollinator visitation and plant species specialisation levels?

Demographic Consequences of Pollen Limitation and Inbreeding Depression in a Gynodioecious Herb

In a gynodioecious plant population, where female and hermaphroditic plants co‐occur, females must produce more seeds or better‐quality offspring than hermaphrodites to be maintained. Further, differences in the magnitude of pollen limitation and inbreeding depression between females and hermaphrodites may affect the relative fitness of the gender morphs and consequently population dynamics. We integrated demographic data into data on pollen limitation and inbreeding depression in a gynodioecious herb. Using a matrix model approach, we then examined the effects of pollen limitation and inbreeding depression on population growth rate and sex ratio. Hermaphrodites tended to contribute more to population growth rates than females. Because of the insensitivity of population growth rates to variation in annual fecundity, pollen limitation of either females or hermaphrodites had a negligible effect on population sex ratio. Inbreeding depression expressed simultaneously in three fitness components of the offspring produced by hermaphrodites reduced stochastic population growth rate and increased female frequency. Given that population growth rates are insensitive to fecundity transitions and that hermaphrodites have moderate selfing rates, our results suggest that inbreeding depression plays a larger role in the maintenance of females in gynodioecious populations than pollen limitation.

Pollinator visitation, pollen limitation, and selection on flower size through female function in contrasting habitats within a population of Campanula persicifolia

We looked at whether flower visitation rates, pollen limitation on seed production, and phenotypic selection on flower size through female function varied across a sharp gradient in light intensity (open meadow vs. forest) within a population of the perennial plant Campanula persicifolia L. (Campanulaceae). Flower visitation rates of putative pollinators were similar in both habitats. Seed number per fruit was strongly pollen limited, with no difference in the magnitude of pollen limitation between the two habitats. This strong pollen limitation set the basis for significant phenotypic selection, through female function, on a trait that probably is important for pollinator attraction: flower size. This was revealed by path analysis and structural equation modelling. The lack of difference in pollen limitation on seed production in the two habitats may be explained by the similarity in flower visitation rates in the two habitats. Moreover, the similarity in pollen limitation in the two habitats probably resulted in a similar magnitude and direction of selection on flower size through female function. Our results suggest that pollen limitation and selection through female function may vary little across space within a popualtion despite large variation in the environmental conditions experienced by plants.