Pollinators may influence plant community assembly through biotic filtering and/or plant–plant competition and facilitation. The relative importance of each process, however, vary according to the ...scale and how strongly plants share their pollinators, and possibly in relation to the pollinator groups considered. We here investigated the assembly of three Atlantic forest hummingbird‐pollinated plant communities across space (among all species in the communities) and time, i.e. yearly flowering phenology (between pairs of co‐flowering species), based on the pairwise distances of multiple floral traits (corolla length, anther and stigma height, colour and nectar). Because tropical hummingbird‐pollinated plants are often subdivided in two pollination niches (hermits versus non‐hermits), we also analyzed these groups separately. We found that trait structure across space was clustered for some floral traits, suggesting biotic filtering and facilitation. All floral traits had weak phylogenetic signal, indicating that closely related species were not more similar than distantly related species. Moreover, floral traits were randomly structured along the phenology when analyzing all plants together. On the other hand, we found similar corolla length but divergent anther height in co‐flowering pairs within the same pollination niche. Thus, plants may benefit from flowering together and avoid competition through fine adjustments in reproductive traits. The results also suggest that clear signals of competition and facilitation among plants are only apparent when species strongly share their pollinators and depending on the traits that are considered. Our study illustrates a complex interplay of biotic filtering, facilitation and competition as processes structuring guilds of plants sharing the same functional group of pollinators.
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Based on recent molecular work by Paudyal & al., the generic limits of the Neotropical woody genus Exostema are reassessed with a view of making them more compatible with traditional, ...morphology‐based generic concepts. A wide circumscription is favoured, congruent with Paudyal & al.'s “clade B” (the Exostema‐Solenandra‐Coutarea‐Hintonia group). Thus defined, Exostema is a genus with 40 species and five natural sections and incorporates three generic splits that were proposed by Paudyal & al. To minimise nomenclatural disruption, a proposal to conserve the name Exostema Rich. against Coutarea Aubl. has been presented separately. Two new combinations at sectional rank are proposed.
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Pathogen transmission mode is a key determinant of epidemiological outcomes. Theory shows that host density can influence the spread of pathogens differentially depending on their mode of ...transmission. Host density could therefore play an important role in determining the pathogen transmission mode. We tested theoretical expectations using floral arrays of the alpine carnation Dianthus pavonius in field experiments of spore dispersal of the anther‐smut fungus, Microbotryum, by vector (pollinator)‐based floral transmission and passive aerial transmission at a range of host densities. Pollinators deposited fewer spores per plant at high host density than at lower density (ranging from a 0.2–2 m spacing between plants), and vector‐based spore deposition at higher densities declined more steeply with distance from diseased plant sources. In contrast, while aerial spore deposition declined with distance from the diseased source, the steepness of this decline was independent of host density. Our study indicates that the amount and distance of vector‐based transmission are likely to be a nonmonotonic function of host density as a result of vector behavior, which is not readily encapsulated by fixed dispersal functions. We conclude that the spatial spread of pathogens by vectors is likely to be greater at lower and intermediate densities, whereas the spatial spread of aerially transmitted pathogens would be greater at high densities. These contrasting patterns could lead to differential importance of each transmission mode in terms of its contribution to subsequent infections across host densities.
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Unrelated organisms that share similar niches often exhibit patterns of convergent evolution in functional traits. Based on bimodal distributions of hawkmoth tongue lengths and tubular white flowers ...in Africa, this study hypothesized that long-tongued hawkmoths comprise a pollination niche (ecological opportunity) that is distinct from that of shorter-tongued hawkmoths.
Field observations, light trapping, camera surveillance and pollen load analysis were used to identify pollinators of plant species with very long-tubed (>8 cm) flowers. The nectar properties and spectral reflectance of these flowers were also measured. The frequency distributions of proboscis length for all captured hawkmoths and floral tube length for a representative sample of night-blooming plant species were determined. The geographical distributions of both native and introduced plant species with very long floral tubes were mapped.
The convolvulus hawkmoth Agrius convolvuli is identified as the most important pollinator of African plants with very long-tubed flowers. Plants pollinated by this hawkmoth species tend to have a very long (approx. 10 cm) and narrow flower tube or spur, white flowers and large volumes of dilute nectar. It is estimated that >70 grassland and savanna plant species in Africa belong to the Agrius pollination guild. In South Africa, at least 23 native species have very long floral tubes, and pollination by A. convolvuli or, rarely, by the closely related hawkmoth Coelonia fulvinotata, has been confirmed for 11 of these species. The guild is strikingly absent from the species-rich Cape floral region and now includes at least four non-native invasive species with long-tubed flowers that are pre-adapted for pollination by A. convolvuli.
This study highlights the value of a niche perspective on pollination, which provides a framework for making predictions about the ecological importance of keystone pollinators, and for understanding patterns of convergent evolution and the role of floral traits in plant colonization.
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Summary
Floral colour mediates plant–pollinator interactions by often signalling floral resources. In this sense, hummingbird‐pollinated flowers are frequently red‐coloured, and there are two ...tentative hypotheses to explain this pattern: 1. hummingbirds are attracted to red due its easier detection and 2. bees are sensorially excluded from red flowers. The second hypothesis is based on bees’ red colour blindness, which lead them to be less frequent and less important than hummingbirds as pollinators of red‐reflecting flowers.
Here, we untangled the role of different flower traits mediating plant–pollinator interactions and empirically tested the above hypotheses. We chose Costus arabicus due to its synchronopatric white‐ and pink‐flowered individuals and its bee and hummingbird pollination system. Although pink flowers are not totally achromatic as pure red ones, they show an achromaticity degree that could drive bee exclusion. Specifically, we tested whether differences on red reflectance work attracting hummingbirds or excluding bees and the consequent implications for the plant's reproduction.
Flower colour morphs of C. arabicus do differ neither in morphology nor in nectar sugar content. Moreover, white and pink flowers can be discriminated by the bees’ and hummingbirds’ colour vision system. Both groups are able to discriminate the red colour variation morph on the flower petals, the white flowers being more easily detected by bees and the pink flowers by hummingbirds. Bees preferentially visited the white flowers, whereas hummingbirds visited both colours at the same rate – both patterns corroborating the second hypothesis.
Pollen loads deposited on stigmas did not differ between flower colour morphs, indicating that bees and hummingbirds play a similar role in the overall pollen deposition. However, bees are more likely to self‐pollinate than hummingbirds. Self‐pollination limits C. arabicus reproduction, and red‐reflecting flowers may be better pollinated by discouraging bee visitation. Therefore, the intraspecific colour variation is driving flowers to show colour‐related different levels of generalization.
Our results support the ‘bee avoidance’ rather than the ‘hummingbird preference’ hypothesis. Sensory exclusion of bees seems to be the pressure for red‐reflecting flowers evolution, driving specialization in hummingbird‐pollinated flowers due to the costs of bee pollination on plant reproduction.
Lay Summary
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26.
Orchid conservation Fay, Michael F.; Pailler, Thierry; Dixon, Kingsley W.
Annals of botany,
09/2015, Volume:
116, Issue:
3
Journal Article
Peer reviewed
Open access
Orchidaceae, one of the largest families of flowering plants, present particular challenges for conservation, due in great part to their often complex interactions with mycorrhizal fungi, pollinators ...and host trees. In this Highlight, we present seven papers focusing on orchids and their interactions and other factors relating to their conservation.
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Ipomoea triloba L., an annual twining herb, is considered an alien invasive species and is distributed all around the globe including tropical Asia. It affects the yield of various economically ...important crops. Studies on floral phenology and reproductive biology are fundamental for the development of management strategies and the conservation of plants. Hence, we investigated the phenology, floral biology, pollen viability, stigma receptivity, pollination mechanism, and reproductive success of I. triloba at two different locations in one of the global biodiversity hotspots. Floral anthesis was diurnal, starting at 6:30 a.m. and lasting until 7:00 a.m. Pollen viability and stigma receptivity were found to coincide, thus suggesting the species was homogamous. The flowers were mostly visited and pollinated by sweat bees (Halictidae), blue‐banded bees (Amegilla sp.), flies (Mesembrius sp.), and butterflies (Appias olferna, Pelopidas agna, and Zizina otis). Further, the pollinator visitation frequency showed a moderately positive correlation with the number of open flowers in both study populations. The plant produced fruits in the absence of pollinators in self‐pollination treatments, indicating a self‐compatible breeding system and dependency on insect pollination for reproductive success. Further, pollen supplementation significantly enhanced the fruit setting and mean seed per fruit at both study sites, suggesting pollen limitation. Additionally, pollen production and pollen/ovule ratio also indicated the facultative autogamous breeding system in I. triloba. Overall, these reproductive characteristics such as mixed mating systems and generalist insect visitation may allow the invasive I. triloba to establish new populations from low numbers of propagules.
Ipomoea triloba was found to be pollen limited with a self‐compatible breeding system. The species was significantly dependent on insect pollinators for its reproductive success.
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The Organization for Tropical Studies (OTS) has played a pivotal role in our understanding of tropical ecosystems' structure and function. For more than fifty years, OTS has contributed to the ...training of three generations of tropical biologists and facilitated, supported, and promoted leading-edge research in its field stations. Plant reproductive ecology and genetics have been a significant focus of OTS research since the early 1960s, and Dr. K.S. Bawa made a significant contribution to the advancement of this field. His work improved our understanding of the diversity and evolution of breeding systems in tropical forests, their phenology and pollination ecology, and their mating and genetic structure. We argue that his work inspired other tropical biologists' work and used the work of one of the authors for illustration when appropriate. We point out the need for research in critically important topics to slow down biodiversity loss, prevent the collapse of tropical systems in a changing climate, and the emergence of zoonotic disease. We suggest future research topics for the OTS field stations, including in plant reproductive biology.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Ecological systematic reviews and meta‐analyses have significantly increased our understanding of global biodiversity decline. However, for some ecological groups, incomplete and biased datasets have ...hindered our ability to construct robust, predictive models. One such group consists of the animal pollinators. Approximately 88% of wild plant species are thought to be pollinated by animals, with an estimated annual value of $230–410 billion dollars. Here we apply text‐analysis to quantify the taxonomic and geographical distribution of the animal pollinator literature, both temporally and spatially. We show that the publication of pollinator literature increased rapidly in the 1980s and 1990s. Taxonomically, we show that the distribution of pollinator literature is concentrated in the honey bees (Apis) and bumble bees (Bombus), and geographically in North America and Europe. At least 25% of pollination‐related s mention a species of honey bee and at least 20% a species of bumble bee, and approximately 46% of s are focussed on either North America (32%) or Europe (14%). Although these results indicate strong taxonomic and geographic biases in the pollinator literature, a large number of studies outside North America and Europe do exist. We then discuss how text‐analysis could be used to shorten the literature search for ecological systematic reviews and meta‐analyses, and to address more applied questions related to pollinator biodiversity, such as the identification of likely interacting plant–pollinator pairs and the number of pollinating species.
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Premise
Understanding the factors that limit reproductive success is a key component of plant biology. Carnivorous plants rely on insects as both nutrient sources and pollinators, providing a unique ...system for studying the effects of both resource and pollen limitation on plant reproduction.
Methods
We conducted a field experiment using wild‐growing Dionaea muscipula J. Ellis (Droseraceae) in which we manipulated prey and pollen in a factorial design and measured flower production, number of fruits, and number of seeds. Because understanding reproduction requires knowledge of a plant species' reproductive and pollination biology, we also examined the pollination system, per‐visit pollinator effectiveness, and pollen‐ovule (P/O) ratio of D. muscipula.
Results
Plants that received supplemental prey produced more flowers than control plants. They also had a higher overall fitness estimate (number of flowers × fruit set (total fruits/total flowers) × seeds per fruit), although this benefit was significant only when prey supplementation occurred in the previous growing season. Neither pollen supplementation nor the interaction between pollen and prey supplementation significantly affected overall plant fitness.
Conclusions
This study reinforces the reliance of D. muscipula on adequate prey capture for flower, fruit, and seed production and a mobile pollen vector for reproduction, indicating the importance of considering insects as part of an effective conservation management plan for this species.
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