1,721,092 research outputs found
Staminal hairs enhance fecundity in the pollen-rewarding self-incompatible lily Bulbine abyssinica
No full textFlowering plants typically use floral rewards to attract animal pollinators. Unlike nectar, pollen rewards are usually visible and may thus function as a signal that influences landing decisions by pollen-seeking insects. Here we artificially manipulate the presence of both pollen and staminal hairs (a putative false signal of pollen reward availability) in the hermaphroditic lily Bulbine abyssinica (Xanthorrhoeaceae) to investigate their effects on bee visitation and fecundity, and also test for trade-offs between pollen production and seed production. Honeybees, the primary floral visitors, are probably not able to distinguish between colours of petals, staminal hairs and pollen of B.abyssinica, according to analysis of reflectance spectra in a bee vision model. Flowers with both pollen and hairs removed had the lowest levels of bee visitation, seed set and seed abortions. Flowers containing hairs had an ~50% increase in visitation rate and seed set compared with emasculated flowers, while intact controls had the highest seed abortion rate. Ovule discounting in intact flowers is probably due to ovarian self-incompatibility (or strong early inbreeding depression) as ovules penetrated by tubes from self-pollen uniformly failed to develop into seeds. These results show that staminal hairs can enhance plant fecundity by increasing attraction of pollen-seeking insects to flowers without increasing the risk of ovule discounting through pollinator-mediated self-pollination
Does the likelihood of an Allee effect on plant fecundity depend on the type of pollinator?
No full textFactors underlying the Allee effect are still heavily debated in ecology. For plants that rely on pollinators for seed production, decreases in conspecific aggregation may reduce attractiveness to floral visitors and lead to an Allee effect. However, floral visitors often differ in their pollination effectiveness; hence, the likelihood of an Allee effect in plant fecundity may depend on how various flower visitors respond to plant aggregation. We tested for Allee effects on fecundity of individuals across two years in the self-incompatible perennial, Kniphofia linearifolia Baker (Xanthorrhoeaceae), which has two distinct types of pollinator, birds and native bees. For this, we used three measures of aggregation; population size, density and isolation. We made replicated pollinator observations in populations of various aggregations and quantified fecundity in these populations. To determine the differences in pollinator effectiveness and assess their contribution to fecundity, we selectively excluded bird visitors from K. linearifolia in these populations. We found that population size, but not density or isolation distance, was associated with increased bird abundance and seed set in one of the two years of the study. Bird visitation rate increased with increased plant aggregation within populations. Fruit set and seed set per flower were positively related to bird visitation rate. The difference in seed set per flower between bird-excluded and unmanipulated plants increased with increasing population size. Although birds were much less frequent visitors than bees (on average 2.1 visits plant-1 h-1 compared to 57.5 visits plant-1 h-1), selective exclusion experiments indicated that birds are consistently the more effective pollinators of this species, and therefore most likely to influence fecundity. Synthesis. In this system, characterised by an Allee effect on plant fecundity, birds were the most effective pollinators, responded positively to plant aggregation and were associated with increased fecundity. Therefore, the responses of effective pollinators to plant aggregation may be a factor that underlies Allee effects on plant fecundity
Emasculation increases seed set in the bird-pollinated hermaphrodite Kniphofia linearifolia (Xanthorrhoeaceae): Evidence for sexual conflict?
No full textPremise of the study: Hermaphroditism in plants can lead to gender conflicts, such as pollen discounting-the loss of siring opportunities following self-pollination, and ovule discounting-the loss of seed production opportunities when self-pollen tubes disable ovules through early inbreeding depression or late-acting self-incompatibility. If ovules are discounted by selfpollination, it can be predicted that emasculation (removal of self-pollen) should increase seed production, as long as pollinators are not deterred by emasculation. Methods: Using the hermaphroditic Kniphofia linearifolia, which belongs to a lineage known to possess late-acting self-incompatibility, we performed hand-pollinations with either self-or cross-pollen and recorded pollen tube growth and seed production. We paired experimentally emasculated plants with non-emasculated controls and quantified pollinator visitation rates, fruit, and seed set in both groups. Key Results: Ovules penetrated by tubes from self-pollen uniformly failed to develop into seeds, as expected from ovarian self-incompatibility (or strong early inbreeding depression). Experimental emasculation had no effect on the rate of visitation by birds, the primary pollinators of this species, but led to increased rejection by bees, which are secondary pollinators. Despite reducing visitation by some pollinators, emasculation led to increased seed production and reduced rates of seed abortion. Conclusions: These results show that female performance in hermaphroditic flowers can be enhanced when flowers are emas culated, even if the overall number of pollinator visits is decreased. The most likely explanation for this effect of emasculation is that it reduces ovule discounting arising from pollinator-mediated self-pollination
Specialized mutualisms may constrain the geographical distribution of flowering plants
No full textIt is commonly assumed that the geographical distributions of plants are governed mainly by abiotic variables. However, interactions with other organisms, such as pollinators, also have the potential to influence plant distributions. To investigate this, we developed niche models for 32 plant taxa that have specialized pollination systems and which are native to a biodiversity hotspot (South Africa). We found that the distributions of these taxa are best explained by a combination of biotic (pollinators) and abiotic factors, rather than by abiotic factors alone. For ~66% of these plant taxa, pollinator distributions were the factor that provided the best predictor of their niches. Furthermore, co-occurrence of these plants and their pollinators, was generally not explained solely by shared abiotic niches, and thus likely reflects broad-scale positive ecological interactions. These results are consistent with the proposal that pollinator distributions may constrain plant distributions and highlight the general potential for species distributions to be shaped by positive interactions with other species. This has important consequences for predicting how distributions of species might change in the face of loss of their key mutualists
FIGURE 3 in Gastrodia madagascariensis (Gastrodieae, Orchidaceae): from an historical designation to a description of a new species from Madagascar
No full textFIGURE 3. Map of Madagascar showing the distribution of the various observations of Gastrodieae on the island. Didymoplexis avaratraensis and D. recurvata, both endemic to Madagascar, co-occur in the northern province of Antsiranana, in evergreen wet forest at mid elevation (Cribb et al. 2013). Didymoplexis verrucosa, also known from South Africa, was recently photographed in the western province of Mahajanga, in deciduous seasonally dry forest (Cribb et al. 2011). Gastrodia madagascariensis occurs in the eastern province of Toamasina opposite the island Nosy Boraha, in evergreen wet forest at low elevation. Filled triangles: flowers observed. Open triangle: only fruits observed.Published as part of Martos, Florent, Johnson, Steven D. & Bytebier, Benny, 2015, Gastrodia madagascariensis (Gastrodieae, Orchidaceae): from an historical designation to a description of a new species from Madagascar, pp. 48-56 in Phytotaxa 221 (1) on page 52, DOI: 10.11646/phytotaxa.221.1.4, http://zenodo.org/record/477967
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Gastrodia R. Br.
No full textKeys to the species of Gastrodia R.Br. in the tropical Afro-Madagascan region (modified from Cribb et al. 2010) 1. Flowers greenish; sepals free for half their length; dorsal sepal markedly shorter than the lateral sepals; petals spatulate; lip with two rugulose calli at base of midlobe.............................................................................................................................. G. africana - Flowers brownish to rarely white; sepals free in apical third only; sepals of equal length; petals ovate or broadly ovate; lip lacking two rugulose calli at base of lip midlobe..........................................................................................................................................2. 2. Callus on lip of three ridges, the middle one highest; column foot with two brownish calli at apex.......................... G. rwandensis - Callus on lip V-shaped, the tip of the V at base of lip midlobe; column foot with two cephaloid tubercular processes at apex.....3. 3. Perianth tube uniformly brown; lip yellow-green with an apricot tip.................................................................................. G. ballii - Perianth tube not uniformly brown; lip yellow-emerald green or orange-green with an emerald green or whitish tip.................. 4. 4. Perianth tube brownish to blackish brown towards the tips; lip yellow-emerald green with a darker tip; cephaloid tubercular processes emerald green........................................................................................................................................ G. madagascariensis 4. Perianth tube brownish to translucent white towards the tips or uniformly white; lip orange-green with a whitish-yellowish tip; cephaloid tubercular processes white................................................................................................................................. G. similisPublished as part of Martos, Florent, Johnson, Steven D. & Bytebier, Benny, 2015, Gastrodia madagascariensis (Gastrodieae, Orchidaceae): from an historical designation to a description of a new species from Madagascar, pp. 48-56 in Phytotaxa 221 (1) on page 53, DOI: 10.11646/phytotaxa.221.1.4, http://zenodo.org/record/477967
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