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Ecology Letters Sep 2022The benefits of animal pollination to crop yield are well known. In contrast, the effects of animal pollination on the spatial or temporal stability (the opposite of... (Meta-Analysis)
Meta-Analysis Review
The benefits of animal pollination to crop yield are well known. In contrast, the effects of animal pollination on the spatial or temporal stability (the opposite of variability) of crop yield remain poorly understood. We use meta-analysis to combine variability information from 215 experimental comparisons between animal-pollinated and wind- or self-pollinated control plants in apple, oilseed rape and faba bean. Animal pollination increased yield stability (by an average of 32% per unit of yield) at between-flower, -plant, -plot and -field scales. Evidence suggests this occurs because yield benefits of animal pollination become progressively constrained closer to the maximum potential yield in a given context, causing clustering. The increase in yield stability with animal pollination is greatest when yield benefits of animal pollination are greatest, indicating that managing crop pollination to increase yield also increases yield stability. These additional pollination benefits have not yet been included in economic assessments but provide further justification for policies to protect pollinators.
Topics: Agriculture; Animals; Brassica napus; Flowers; Insecta; Pollination
PubMed: 35843226
DOI: 10.1111/ele.14069 -
PeerJ 2022Changes in environmental conditions are likely to have a complex effect on the growth of plants, their phenology, plant-pollinator interactions, and reproductive...
Changes in environmental conditions are likely to have a complex effect on the growth of plants, their phenology, plant-pollinator interactions, and reproductive success. The current world is facing an ongoing climate change along with other human-induced environmental changes. Most research has focused on the impact of increasing temperature as a major driving force for climate change, but other factors may have important impacts on plant traits and pollination too and these effects may vary from season to season. In addition, it is likely that the effects of multiple environmental factors, such as increasing temperature, water availability, and nitrogen enrichment are not independent. Therefore, we tested the impact of two key factors-water, and nitrogen supply-on plant traits, pollination, and seed production in (Brassicaceae) in three seasons defined as three temperature conditions with two levels of water and nitrogen supply in a factorial design. We collected data on multiple vegetative and floral traits and assessed the response of pollinators in the field. Additionally, we evaluated the effect of growing conditions on seed set in plants exposed to pollinators and in hand-pollinated plants. Our results show that water stress impaired vegetative growth, decreased flower production, and reduced visitation by pollinators and seed set, while high amount of nitrogen increased nectar production under low water availability in plants grown in the spring. Temperature modulated the effect of water and nitrogen availability on vegetative and floral traits and strongly affected flowering phenology and flower production. We demonstrated that changes in water and nitrogen availability alter plant vegetative and floral traits, which impacts flower visitation and consequently plant reproduction. We conclude that ongoing environmental changes such as increasing temperature, altered precipitation regimes and nitrogen enrichment may thus affect plant-pollinator interactions with negative consequences for the reproduction of wild plants and insect-pollinated crops.
Topics: Humans; Pollination; Sinapis; Brassicaceae; Dehydration; Crops, Agricultural
PubMed: 35462774
DOI: 10.7717/peerj.13009 -
Trends in Ecology & Evolution Jul 2021Multiple global change pressures, and their interplay, cause plant-pollinator extinctions and modify species assemblages and interactions. This may alter the risks of... (Review)
Review
Multiple global change pressures, and their interplay, cause plant-pollinator extinctions and modify species assemblages and interactions. This may alter the risks of pathogen host shifts, intra- or interspecific pathogen spread, and emergence of novel population or community epidemics. Flowers are hubs for pathogen transmission. Consequently, the structure of plant-pollinator interaction networks may be pivotal in pathogen host shifts and modulating disease dynamics. Traits of plants, pollinators, and pathogens may also govern the interspecific spread of pathogens. Pathogen spillover-spillback between managed and wild pollinators risks driving the evolution of virulence and community epidemics. Understanding this interplay between host-pathogen dynamics and global change will be crucial to predicting impacts on pollinators and pollination underpinning ecosystems and human wellbeing.
Topics: Ecosystem; Epidemics; Flowers; Humans; Plants; Pollination
PubMed: 33865639
DOI: 10.1016/j.tree.2021.03.006 -
Proceedings. Biological Sciences Apr 2022Modern agriculture is becoming increasingly pollinator-dependent. However, the global stock of domesticated honeybees is growing at a slower rate than its demand, while... (Meta-Analysis)
Meta-Analysis
Modern agriculture is becoming increasingly pollinator-dependent. However, the global stock of domesticated honeybees is growing at a slower rate than its demand, while wild bees are declining worldwide. This uneven scenario of high pollinator demand and low pollinator availability can translate into increasing pollination limitation, reducing the yield of pollinator-dependent crops. However, overall assessments of crop pollination limitation and the factors determining its magnitude are missing. Based on 52 published studies including 30 crops, we conducted a meta-analysis comparing crop yield in pollen-supplemented versus open-pollinated flowers. We assessed the overall magnitude of pollination limitation and whether this magnitude was influenced by (i) the presence/absence of managed honeybees, (ii) crop compatibility system (i.e. self-compatible/self-incompatible) and (iii) the interaction between these two factors. Overall, pollen supplementation increased yield by approximately 34%, indicating sizable pollination limitation. Deployment of managed honeybees and self-compatibility were associated with lower pollination limitation. Particularly, active honeybee management decreased pollination limitation among self-compatible but apparently not among self-incompatible crops. These findings indicate that current pollination regimes are, in general, inadequate to maximize crop yield, even when including managed honeybees, and stress the need of transforming the pollination management paradigm of agricultural landscapes.
Topics: Agriculture; Animals; Bees; Crops, Agricultural; Flowers; Pollen; Pollination
PubMed: 35382601
DOI: 10.1098/rspb.2022.0086 -
Ecological Applications : a Publication... Jan 2023There is increasing evidence that farmers in many areas are achieving below maximum yields due to insufficient pollination. Practical and effective approaches are needed...
There is increasing evidence that farmers in many areas are achieving below maximum yields due to insufficient pollination. Practical and effective approaches are needed to maintain wild pollinator populations within agroecosystems so they can deliver critical pollination services that underpin crop production. We established nesting and wildflower habitat interventions in 24 UK apple orchards and measured effects on flower-visiting insects and the pollination they provide, exploring how this was affected by landscape context. We quantified the extent of pollination deficits and assessed whether the management of wild pollinators can reduce deficits and deliver improved outcomes for growers over 3 years. Wildflower interventions increased solitary bee numbers visiting apple flowers by over 20%, but there was no effect of nesting interventions. Other pollinator groups were influenced by both local and landscape-scale factors, with bumblebees and hoverflies responding to the relative proportion of semi-natural habitat at larger spatial scales (1000 m), while honeybees and other flies responded at 500 m or less. By improving fruit number and quality, pollinators contributed more than £16 k per hectare. However, deficits (where maximum potential was not being reached due to a lack of pollination) were recorded and the extent of these varied across orchards, and from year to year, with a 22% deficit in output in the worst (equivalent to ~£14 k/ha) compared to less than 3% (equivalent to ~£2 k/ha) in the best year. Although no direct effect of our habitat interventions on deficits in gross output was observed, initial fruit set and seed set deficits were reduced by abundant bumblebees, and orchards with a greater abundance of solitary bees saw lower deficits in fruit size. The abundance of pollinators in apple orchards is influenced by different local and landscape factors that interact and vary between years. Consequently, pollination, and the extent of economic output deficits, also vary between orchards and years. We highlight how approaches, including establishing wildflower areas and optimizing the ratio of cropped and non-cropped habitats can increase the abundance of key apple pollinators and improve outcomes for growers.
Topics: Bees; Animals; Pollination; Ecosystem; Insecta; Fruit; Malus; Crops, Agricultural; Flowers
PubMed: 36107148
DOI: 10.1002/eap.2743 -
Ecological Applications : a Publication... Sep 2022Loss of habitats and native species, introduction of invasive species, and changing climate regimes lead to the homogenization of landscapes and communities, affecting...
Loss of habitats and native species, introduction of invasive species, and changing climate regimes lead to the homogenization of landscapes and communities, affecting the availability of habitats and resources for economically important guilds, such as pollinators. Understanding how pollinators and their interactions vary along resource diversity gradients at different scales may help to determine their adaptability to the current diversity loss related to global change. We used data on 20 plant-pollinator communities along gradients of flower richness (local diversity) and landscape heterogeneity (landscape diversity) to understand how the diversity of resources at local and landscape scales affected (1) wild pollinator abundance and richness (accounting also for honey bee abundance), (2) the structure of plant-pollinator networks, (3) the proportion of actively selected interactions (those not occurring by neutral processes), and (4) pollinator diet breadth and species' specialization in networks. Wild pollinator abundance was higher overall in flower-rich and heterogeneous habitats, while wild pollinator richness increased with flower richness (more strongly for beetles and wild bees) and decreased with honeybee abundance. Network specialization (H '), modularity, and functional complementarity were all positively related to floral richness and landscape heterogeneity, indicating niche segregation as the diversity of resources increases at both scales. Flower richness also increased the proportion of actively selected interactions (especially for wild bees and flies), whereas landscape heterogeneity had a weak negative effect on this variable. Overall, network-level metrics responded to larger landscape scales than pollinator-level metrics did. Higher floral richness resulted in a wider taxonomic and functional diet for all the study guilds, while functional diet increased mainly for beetles. Despite this, specialization in networks (d') increased with flower richness for all the study guilds, because pollinator species fed on a narrower subset of plants as communities became richer in species. Our study indicates that pollinators are able to adapt their diet to resource changes at local and landscape scales. However, resource homogenization might lead to poor and generalist pollinator communities, where functionally specialized interactions are lost. This study highlights the importance of including different scales to understand the effects of global change on pollination service through changes in resource diversity.
Topics: Animals; Bees; Coleoptera; Diet; Ecosystem; Flowers; Plants; Pollination
PubMed: 35403772
DOI: 10.1002/eap.2634 -
Plant Biology (Stuttgart, Germany) Aug 2022Bird pollination systems are diverse, ranging from narrow-tubed flowers pollinated by specialist nectarivores such as hummingbirds and sunbirds, to relatively open...
Bird pollination systems are diverse, ranging from narrow-tubed flowers pollinated by specialist nectarivores such as hummingbirds and sunbirds, to relatively open flowers pollinated by opportunistic (i.e. generalist) nectarivores. The role of opportunistic avian nectarivores as pollinators has historically been under-appreciated. A key aspect to understanding the importance of opportunistic birds as pollinators is to investigate how efficiently they transfer pollen among flowers. Here, we document the pollination and breeding systems of Schotia brachypetala, a southern African tree known as the 'weeping boer-bean' on account of its prolific production of dilute hexose-dominated nectar. The cup-shaped flowers of this tree attract a large number of bird species, including both opportunistic and specialist nectarivores. We identified floral visitors using observations and camera traps and quantified the floral traits responsible for animal attraction. We documented the breeding system, used selective pollinator exclusion to test the contribution of birds to fecundity, and performed supplemental pollination to test for pollen limitation. Single-visit pollen deposition trials were undertaken to determine the efficacy of bird pollinators. Controlled hand-pollination experiments showed that S. brachypetala is genetically self-incompatible and therefore dependent on pollinators for seed production. Supplemental hand-pollination experiments showed that natural fecundity is limited by either the amount and/or the quality of pollen on stigmas. Flowers from which birds but not insects were experimentally excluded set fewer seeds than open control flowers. Opportunistic birds deposited more pollen per visit than did specialist sunbirds. We conclude that S. brachypetala has a generalized bird pollination system that mainly involves opportunistic nectarivores.
Topics: Animals; Fabaceae; Flowers; Passeriformes; Plant Breeding; Plant Nectar; Pollination; Trees
PubMed: 35500151
DOI: 10.1111/plb.13433 -
Current Biology : CB Oct 2018In order to survive and reproduce, flowering plants must balance the conflicting selective pressures of herbivore avoidance and pollinator attraction. Links between... (Review)
Review
In order to survive and reproduce, flowering plants must balance the conflicting selective pressures of herbivore avoidance and pollinator attraction. Links between herbivory and reproduction are often attributed to indirect effects of leaf damage on pollination via reductions in floral allocation, or increases in chemical defenses on herbivore-damaged plants. However, the impacts of herbivory on pollinators have the potential to extend beyond initial floral visits when plant defenses impact pollinator health, foraging behavior, and reproductive success. Here, we examine important but underexplored ways in which herbivory may alter floral phenotype and thus impact pollinators. First, we outline genetic and biochemical mechanisms predicted to underlie floral changes following herbivory, as they impact the floral resources (nectar and pollen) sought by pollinators. Next, we discuss how the consumption of secondary compounds might impact pollinator fitness, including carryover effects on subsequent foraging, mating success, and transgenerational effects on offspring. We consider how pollinator health, life history, and coevolutionary history might result in context-dependent impacts of plant defensive chemistry on pollinator fitness. Finally, we call for studies that measure the impact of herbivore-induced plant defenses on the full spectrum of flower visitors, and contrast case studies on conventional pollinators (for example, generalized bees) versus insects whose larvae are herbivores on the same plants that adults pollinate (such as several butterflies and moths). By linking these consequences of herbivory to fitness effects on both herbivores and pollinators, we will better understand how coevolution between plants, herbivores, and pollinators shapes both defensive and reproductive plant traits.
Topics: Animals; Biological Evolution; Flowers; Herbivory; Insecta; Plant Leaves; Plant Nectar; Pollen; Pollination; Reproduction
PubMed: 30300606
DOI: 10.1016/j.cub.2018.08.010 -
American Journal of Botany Jan 2020Variation in pollen-ovule ratios is thought to reflect the degree of pollen transfer efficiency-the more efficient the process, the fewer pollen grains needed. Few...
PREMISE
Variation in pollen-ovule ratios is thought to reflect the degree of pollen transfer efficiency-the more efficient the process, the fewer pollen grains needed. Few studies have directly examined the relationship between pollen-ovule ratio and pollen transfer efficiency. For active pollination in the pollination brood mutualisms of yuccas and yucca moths, figs and fig wasps, senita and senita moths, and leafflowers and leafflower moths, pollinators purposefully collect pollen and place it directly on the stigmatic surface of conspecific flowers. The tight coupling of insect reproductive interests with pollination of the flowers in which larvae develop ensures that pollination is highly efficient.
METHODS
We used the multiple evolutionary transitions between passive pollination and more efficient active pollination to test if increased pollen transfer efficiency leads to reduced pollen-ovule ratios. We collected pollen and ovule data from a suite of plant species from each of the pollination brood mutualisms and used phylogenetically controlled tests and sister-group comparisons to examine whether the shift to active pollination resulted in reduced pollen-ovule ratios.
RESULTS
Across all transitions between passive and active pollination in plants, actively pollinated plants had significantly lower pollen-ovule ratios than closely related passively pollinated taxa. Phylogenetically corrected comparisons demonstrated that actively pollinated plant species had an average 76% reduction in the pollen-ovule ratio.
CONCLUSIONS
The results for active pollination systems support the general utility of pollen-ovule ratios as indicators of pollination efficiency and the central importance of pollen transfer efficiency in the evolution of pollen-ovule ratio.
Topics: Animals; Flowers; Ovule; Pollen; Pollination; Symbiosis
PubMed: 31889299
DOI: 10.1002/ajb2.1412 -
Philosophical Transactions of the Royal... Jun 2022Despite a substantial increase in scientific, public and political interest in pollinator health and many practical conservation efforts, incorporating initiatives... (Review)
Review
Despite a substantial increase in scientific, public and political interest in pollinator health and many practical conservation efforts, incorporating initiatives across a range of scales and sectors, pollinator health continues to decline. We review existing pollinator conservation initiatives and define their common structural elements. We argue that implementing effective action for pollinators requires further scientific understanding in six key areas: (i) status and trends of pollinator populations; (ii) direct and indirect drivers of decline, including their interactions; (iii) risks and co-benefits of pollinator conservation actions for ecosystems; (iv) benefits of pollinator conservation for society; (v) the effectiveness of context-specific, tailored, actionable solutions; and (vi) integrated frameworks that explicitly link benefits and values with actions to reverse declines. We propose use of the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) conceptual framework to link issues and identify critical gaps in both understanding and action for pollinators. This approach reveals the centrality of addressing the recognized drivers of decline, such as patterns of global trade and demography, which are frequently overlooked in current pollinator conservation efforts. Finally, we discuss how existing and new approaches in research can support efforts to move beyond these shortcomings in pollinator conservation initiatives. This article is part of the theme issue 'Natural processes influencing pollinator health: from chemistry to landscapes'.
Topics: Biodiversity; Ecosystem; Pollination
PubMed: 35491595
DOI: 10.1098/rstb.2021.0165