Pollen limitation and reproduction varies with population size in experimental populations of Sabatia angularis (Gentianaceae)

Botany ◽  
2009 ◽  
Vol 87 (3) ◽  
pp. 330-338 ◽  
Author(s):  
Rachel B. Spigler ◽  
Shu-Mei Chang
Keyword(s):  
Reproductive Success ◽  
Population Size ◽  
Intraspecific Competition ◽  
Seed Set ◽  
Pollen Limitation ◽  
Small Populations ◽  
Plant Populations ◽  
Large Populations ◽  
Fruit And Seed Set ◽  
Supplemental Pollination

Individuals in large plant populations are expected to benefit from increased reproductive success relative to those in small populations because of the facilitative effects of large aggregations on pollination. As populations become small, the inability to attract sufficient numbers of pollinators can reduce reproduction via pollen limitation. This study experimentally tested whether such trends occur for the herbaceous biennial Sabatia angularis (L.) Pursh (Gentianaceae). We created artificial populations of varying size consisting of potted S. angularis plants in two field sites to determine whether population size affected mean fruit and seed set. We also examined whether population size affected the degree of pollen limitation using a supplemental pollination design in one of the sites. Our results showed that, on average, seed set was lower in large populations, not small populations, of S. angularis and that this result may be due to increased pollen limitation in large populations. We suggest that in certain contexts, small populations may enjoy reproductive advantages over large populations by escaping intraspecific competition for pollinators.

scholarly journals Spatiotemporal Variations in Seed Set and Pollen Limitation in Populations of the Rare Generalist Species Polemonium caeruleum in Poland

2022 ◽  
Vol 12 ◽  
Author(s):  
Justyna Ryniewicz ◽  
Katarzyna Roguz ◽  
Paweł Mirski ◽  
Emilia Brzosko ◽  
Mateusz Skłodowski ◽  
...  
Keyword(s):  
Reproductive Success ◽  
Population Size ◽  
Seed Production ◽  
Seed Set ◽  
Pollen Limitation ◽  
Monthly Precipitation ◽  
Small Populations ◽  
Flower Visitors ◽  
Visitation Frequency ◽  
Average Monthly Precipitation

A vast majority of angiosperms are pollinated by animals, and a decline in the number and diversity of insects often affects plant reproduction through pollen limitation. This phenomenon may be particularly severe in rare plant species, whose populations are shrinking. Here, we examined the variability in factors shaping reproductive success and pollen limitation in red-listed Polemonium caeruleum L. During a 5-year study in several populations of P. caeruleum (7–15, depending on year), we assessed the degree of pollen limitation based on differences in seed set between open-pollinated (control) and hand-pollinated flowers. We analysed the effects of flower visitors, population size, and meteorological data on plant reproductive success and pollen limitation. Our study showed that pollen limitation rarely affected P. caeruleum populations, and was present mainly in small populations. Pollen limitation index was negatively affected by the size of population, visitation frequency of all insects, and when considering the visitation frequency of individual groups, also by honeybee visits. Seed production in control treatment was positively influenced by the population size, average monthly precipitation in June and visits of hoverflies, while visits of honeybees, average monthly temperature in September, and average monthly precipitation in August influenced seed production negatively. As generalist plant P. caeruleum can be pollinated by diverse insect groups, however, in small populations their main visitors, the honeybees and bumblebees, may be less attracted, eventually leading to the disappearance of these populations. In pollination of P. caeruleum managed honeybees may play a dual role: while they are the most frequent and efficient flower visitors, their presence decreases seed set in open-pollinated flowers, which is most probably related to efficient pollen collection by these insects.

scholarly journals Population size, habitat fragmentation, and the nature of adaptive variation in a stream fish

2014 ◽  
Vol 281 (1790) ◽  
pp. 20140370 ◽  
Author(s):  
Dylan J. Fraser ◽  
Paul V. Debes ◽  
Louis Bernatchez ◽  
Jeffrey A. Hutchings
Keyword(s):  
Genetic Variation ◽  
Habitat Fragmentation ◽  
Population Size ◽  
Brook Trout ◽  
Small Populations ◽  
Adaptive Genetic Variation ◽  
Genetic Population ◽  
Fragmented Populations ◽  
Large Populations ◽  
Adaptive Differentiation

Whether and how habitat fragmentation and population size jointly affect adaptive genetic variation and adaptive population differentiation are largely unexplored. Owing to pronounced genetic drift, small, fragmented populations are thought to exhibit reduced adaptive genetic variation relative to large populations. Yet fragmentation is known to increase variability within and among habitats as population size decreases. Such variability might instead favour the maintenance of adaptive polymorphisms and/or generate more variability in adaptive differentiation at smaller population size. We investigated these alternative hypotheses by analysing coding-gene, single-nucleotide polymorphisms associated with different biological functions in fragmented brook trout populations of variable sizes. Putative adaptive differentiation was greater between small and large populations or among small populations than among large populations. These trends were stronger for genetic population size measures than demographic ones and were present despite pronounced drift in small populations. Our results suggest that fragmentation affects natural selection and that the changes elicited in the adaptive genetic composition and differentiation of fragmented populations vary with population size. By generating more variable evolutionary responses, the alteration of selective pressures during habitat fragmentation may affect future population persistence independently of, and perhaps long before, the effects of demographic and genetic stochasticity are manifest.

The reproductive ecology of island populations of distylous Menyanthes trifoliata (Menyanthaceae)

1998 ◽  
Vol 76 (5) ◽  
pp. 818-828 ◽  
Author(s):  
Faye L Thompson ◽  
Luise A Hermanutz ◽  
David J Innes
Keyword(s):  
Seed Set ◽  
Aquatic Macrophyte ◽  
Pollen Limitation ◽  
Bimodal Distribution ◽  
Stabilizing Selection ◽  
Long Distance ◽  
Anther Length ◽  
Reciprocal Arrangement ◽  
Fruit And Seed Set ◽  
Menyanthes Trifoliata

Menyanthes trifoliata L. is a distylous, clonal aquatic macrophyte found in shallow bogs and river margins throughout the boreal ecosystem, including the island of Newfoundland. A combination of long-distance dispersal and colonization after deglaciation, and pollen limitation resulting from reduced pollinator diversity and abundance documented on islands, predicts the breakdown of heterostyly to favour the establishment of self-compatible homostyles on islands. To test if self-fertilizing homostyles have been selected, variation in floral characters and compatibility relationships were examined in M. trifoliata populations from the Avalon Peninsula of Newfoundland. Morph ratio and its effect on fruit and seed set were examined in nine populations. Of the seven dimorphic populations, morphs occurred in a 1:1 ratio in four populations and deviated significantly from a 1:1 ratio in three populations. The two populations monomorphic for either pin or thrum morphs set few fruits or seeds (<15%). A strictly reciprocal arrangement of stigma height and anther length was not observed between pin and thrum morphs in the majority of populations studied. Stigma-anther separation showed a bimodal distribution with few intermediate "homostylous" flowers, rather than the discreet bimodal distribution typical of distylous species. Fruit and seed set were high (>60%) in equal morph ratio populations and were not significantly correlated to stigma-anther separation, indicating that there was no selective advantage of being homostylous. All three populations tested were highly self-incompatible, confirming that there has not been a breakdown of heterostyly on the island of Newfoundland. A reduced pollinator fauna typical of island environments may have relaxed stabilizing selection for strict herkogamy between floral morphs, resulting in the observed lack of reciprocity.Key words: Menyanthes trifoliata, distyly, homostyle, reciprocal herkogamy, clonal aquatic macrophyte, island of Newfoundland.

Interaction of nutrient supply and plant density in relation to maximal yield of the swede crop

1968 ◽  
Vol 70 (3) ◽  
pp. 369-373 ◽  
Author(s):  
R. W. Lang ◽  
J. C. Holmes
Keyword(s):  
Plant Density ◽  
Total Yield ◽  
Nutrient Supply ◽  
Matter Content ◽  
Human Consumption ◽  
Dry Matter Content ◽  
Small Populations ◽  
Plant Populations ◽  
Maximal Yield ◽  
Large Populations

SUMMARYThe effects of changing plant density and nutrient supply on the yield of swedes were measured in nine experiments over 3 years. With small populations, a large nutrient supply was required to reach the maximal yield of roots, but with large plant populations the same nutrient rate depressed yield. This interaction is illustrated by a response surface, and reasons for it are discussed. The interaction is of limited importance in practice because it was small over the range of population and nutrient supply commonly used. Even with small populations, the compensation achieved by applying more fertilizer was uneconomic. On crops with large populations, such as swedes for human consumption, however, the normal recommended rate of fertilizer should not be exceeded because of loss of yield as well as increased cost. More fertilizer and greater plant density were needed to give maximal total yield (roots + tops) than of roots alone. Effects of nutrient supply and plant population on plant establishment and dry-matter content of the swedes are discussed.

Causes of Low Fruit and Seed Set in Bird-Pollinated Anagyris foetida (Leguminosae): Pollen Limitation and Other Extrinsic Factors

2009 ◽  
Vol 45 (1) ◽  
pp. 77-94 ◽  
Author(s):  
Francisco J. Valtueña ◽  
Ana Ortega-Olivencia ◽  
Tomás Rodríguez-Riaño ◽  
Josefa López
Keyword(s):  
Seed Set ◽  
Pollen Limitation ◽  
Extrinsic Factors ◽  
Fruit And Seed Set

scholarly journals Relationships between population size and pollen fates in a moth-pollinated orchid

2009 ◽  
Vol 5 (2) ◽  
pp. 282-285 ◽  
Author(s):  
Steven D Johnson ◽  
Erica Torninger ◽  
Jon Ågren
Keyword(s):  
Population Size ◽  
Fruit Set ◽  
Small Populations ◽  
Allee Effects ◽  
Plant Populations ◽  
Small Plant ◽  
Orchid Species ◽  
Pollination Success ◽  
Self Pollination

Management of small plant populations requires an understanding of their reproductive ecology, particularly in terms of sensitivity to Allee effects. To address this issue, we explored how components of pollen transfer and pollination success of individual plants varied among 36 populations of the self-compatible moth-pollinated orchid Satyrium longicauda in South Africa. Mean fruit set, seed production, proportion of flowers with pollen deposited or removed and proportion of removed pollen that reached stigmas (approx. 8% in this species) were not significantly related to population size (range: 1–450 flowering individuals), density or isolation. Plants in small populations did, however, have significantly higher levels of pollinator-mediated self-pollination (determined using colour-labelled pollen) than those in larger populations. Our results suggest that small populations of this orchid species are resilient to Allee effects in terms of overall pollination success, although the higher levels of pollinator-mediated self-pollination in small populations may lead to inbreeding depression and long-term erosion of genetic diversity.

scholarly journals Population-size-dependent, age-structured branching processes linger around their carrying capacity

2011 ◽  
Vol 48 (A) ◽  
pp. 249-260
Author(s):  
Peter Jagers ◽  
Fima C. Klebaner
Keyword(s):  
Population Size ◽  
Carrying Capacity ◽  
Branching Process ◽  
Branching Processes ◽  
Critical Threshold ◽  
Small Populations ◽  
Size Dependent ◽  
Large Populations ◽  
Age Structured ◽  
Process Context

Dependence of individual reproduction upon the size of the whole population is studied in a general branching process context. The particular feature under scrutiny is that of reproduction changing from supercritical in small populations to subcritical in large populations. The transition occurs when the population size passes a critical threshold, known in ecology as the carrying capacity. We show that populations either die out directly, never coming close to the carrying capacity, or grow quickly towards the carrying capacity, subsequently lingering around it for a time that is expected to be exponentially long in terms of a carrying capacity tending to infinity.

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