The ecological pollination syndromes of insect-pollinated plants in an alpine meadow

The insect pollination of an alpine plant community consisting of herbs and shrubs, was observed on Mt. Kisokoma-ga-take, central Honshu, Japan. There were two main groups of pollinators, syrphid flies and bumble bees. Although some shrubs were visited by both types of insects, other shrubs and the herbs were visited by either syrphid flies or bumble bees. Two types of herbs categorized by the difference of flower-visiting insects, the Syrphid-type and the Bombus-type, exhibited some clearly contrasting ecological characteristics such as the flowering behavior of individual plants, spatial distribution of the plant populations and segregation of flowering phenology at the community level. The Syrphid-type herbs were densely distributed throughout wide areas in the tall herb stand, and all the flowers borne by an individual plant bloomed simultaneously. Each species did not markedly segregate its flowering time from that of other species of the same type. The Bombus-type herbs were distributed locally and/or at low density, and the individual flowers borne by an individual plant showed staggered flowering times. Each species had a more strictly segregated flowering time. These ecological characteristics of these two flower types seemed to be related to the behavioral characteristics of their pollinators.     

Pollination of the orchidEpipactis thunbergii by syrphid flies (Diptera: Syrphidae)

The behavior of visitors to the flowers of the orchidEpipactis thunbergii was studied, with special attention to the role of the epichile in the pollination process. Only four species of syrphid flies legitimately pollinated the flower, among whichSphaerophoria macrogaster was regarded as the most effective pollinator. The movable epichile, possessing a furrow at its base, played a critical role in the pollination process: it threw the syrphid fly onto the stigmatic surface when both sides of the basal slanting surface of the furrow were presumably pressed in the direction of the hypochile by the fore (and middle) legs of the retreating syrphid fly. At this moment, the fly received a set of pollinia on the thorax.     

Pollinator aggregative and functional responses to flower density: does pollinator response to patches of plants accelerate at low‐densities?

Plant reproduction is often reduced at low densities, due to reduced pollinator visitation rates. Recent theory suggests that a disproportionate increase in pollinator visits to patches of plants as heterospecific plant density increases (i.e. if visitation is a sigmoid function of patch density) can rescue sparse populations of a focal plant species from reduced reproductive success or population decline. A field experiment was performed to determine the shape of the pollinator visitation response to patches of differing density of the common weed Brassica rapa . Both the aggregative and functional response for the entire pollinator community were saturating rather than sigmoid, indicating that pollinator response does not accelerate when density increases. The results for the entire pollinator community were consistent among temporal and spatial replicates. Aggregative response curves for specific pollinator taxa were either linear (bombyliid flies) or saturating (syrphid flies, solitary bees, and Lepidoptera). Functional responses for these taxa were saturating (syrphid flies and solitary bees) or flat (bombyliid flies and Lepidoptera). Individual pollinators visited more plants during foraging bouts in high-density patches, but visits per plant decreased. Seeds per fruit and seeds per flower increased with increasing density. There is no evidence that pollinators disproportionately visit denser patches, or that the conditions for this mechanism of pollination facilitation are likely to be met in this generalist pollinator system.     

Resource heterogeneity, diet shifts and intra-cohort competition: effects on size divergence in YOY fish

The pollination syndrome hypothesis has provided a major conceptual framework for how plants and pollinators interact. However, the assumption of specialization in pollination systems and the reliability of floral traits in predicting the main pollinators have been questioned recently. In addition, the relationship between ecological and evolutionary specialization in pollination interactions is still poorly understood. We used data of 62 plant species from three communities across southern Norway to test: (1) the relationships between floral traits and the identity of pollinators, (2) the association between floral traits (evolutionary specialization) and ecological generalization, and (3) the consistency of both relationships across communities. Floral traits significantly affected the identity of pollinators in the three communities in a way consistent with the predictions derived from the pollination syndrome concept. However, hover flies and butterflies visited flowers with different shapes in different communities, which we mainly attribute to among-community variation in pollinator assemblages. Interestingly, ecological generalization depended more on the community-context (i.e. the plant and pollinator assemblages in the communities) than on specific floral traits. While open yellow and white flowers were the most generalist in two communities, they were the most specialist in the alpine community. Our results warn against the use of single measures of ecological generalization to question the pollination syndrome concept, and highlight the importance of community comparisons to assess the pollination syndromes, and to understand the relationships between ecological and evolutionary specialization in plant-pollinator interactions.     

Fly pollination of dichogamous Angelica sylvestris (Apiaceae): how (functionally) specialized can a (morphologically) generalized plant be?

Because of the flower morphology and high number of insect visitors, plants of the family Apiaceae are regarded as generalists in terms of pollination systems. Recent studies however showed some degree of, at least, ecological specialization in some members of this taxonomical group and indicated interesting patterns of insect visitor behavior: discrimination between umbel sexual phases. To test whether this is true in case of other members of the family, over two years we studied the pollination biology of a common European umbellifer, Angelica sylvestris, a species considered by some authors as a supergeneralist. Although its flowers were visited by over 70 species of insects grouped in 10 morphospecies, only a relatively narrow assemblage of muscoid and syrphid flies, rather constant in both study years, contributed to pollination. These insects did not exhibit any preferences toward plant sexual phases. Based on our results and available literature, we discuss the concept of specialization/generalization of the A. sylvestris pollination system, especially in the context of the ??unspecialized?? floral morphology characteristic for members of the Carrot family.     

具有年龄结构的食蚜蝇-蚜虫捕食模型

现有的具有年龄结构的捕食-食饵模型总是假设只有成年捕食者捕食猎物,这与实际情况不符。建立了一个幼年捕食者捕食食饵的具有年龄结构的食蚜蝇-蚜虫模型,应用微分方程定性理论,讨论了系统平衡点及其稳定性:其中平衡点E1(0,0,0)为不稳定的;满足一定条件时,边界平衡点E2(K,0,0)及正平衡点E3(x*,y1*,y2*)为局部渐近稳定的;且应用一致持续生存理论得到了系统永久持续生存的条件,为有害生物综合治理提供了理论依据。     

Differential effects of jasmonic acid treatment of Brassica nigra on the attraction of pollinators, parasitoids, and butterflies

Herbivore-induced plant defences influence the behaviour of herbivores as well as that of their natural enemies. Jasmonic acid is one of the key hormones involved in both these direct and indirect induced defences. Jasmonic acid treatment of plants changes the composition of defence chemicals in the plants, induces volatile emission, and increases the production of extrafloral nectar. However, few studies have addressed the potential influence of induced defences on flower nectar chemistry and pollinator behaviour. These have shown that herbivore damage can affect pollination rates and plant fitness. Here, we have investigated the effect of jasmonic acid treatment on floral nectar production and the attraction of pollinators, as well as the effect on the behaviour of an herbivore and its natural enemy. The study system consisted of black mustard plants, Brassica nigra L. (Brassicaceae), pollinators of Brassica nigra (i.e., honeybees and syrphid flies), a specialist herbivore, Pieris rapae L. (Lepidoptera: Pieridae), and a parasitoid wasp that uses Pieris larvae as hosts, Cotesia glomerata L. (Hymenoptera: Braconidae). We show that different trophic levels are differentially affected by jasmonic acid-induced changes. While the herbivore prefers control leaves over jasmonic acid-treated leaves for oviposition, the parasitoid C. glomerata is more attracted to jasmonic acid-treated plants than to control plants. We did not observe differences in pollinator preference, the rates of flower visitation by honeybees and syrphid flies were similar for control and jasmonic acid-treated plants. Plants treated with jasmonic acid secreted less nectar than control plants and the concentrations of glucose and fructose tended to be lower than in nectar from control plants. Jasmonic acid treatment resulted in a lower nectar production than actual feeding damage by P. rapae caterpillars.     

Phenotypic selection on flowering phenology and pollination efficiency traits between Primula populations with different pollinator assemblages

Floral traits have largely been attributed to phenotypic selection in plant–pollinator interactions. However, the strength of this link has rarely been ascertained with real pollinators. We conducted pollinator observations and estimated selection through female fitness on flowering phenology and floral traits between two Primula secundiflora populations. We quantified pollinator‐mediated selection by subtracting estimates of selection gradients of plants receiving supplemental hand pollination from those of plants receiving open pollination. There was net directional selection for an earlier flowering start date at populations where the dominant pollinators were syrphid flies, and flowering phenology was also subjected to stabilized quadratic selection. However, a later flowering start date was significantly selected at populations where the dominant pollinators were legitimate (normal pollination through the corolla tube entrance) and illegitimate bumblebees (abnormal pollination through nectar robbing hole which located at the corolla tube), and flowering phenology was subjected to disruptive quadratic selection. Wider corolla tube entrance diameter was selected at both populations. Furthermore, the strength of net directional selection on flowering start date and corolla tube entrance diameter was stronger at the population where the dominant pollinators were syrphid flies. Pollinator‐mediated selection explained most of the between‐population variations in the net directional selection on flowering phenology and corolla tube entrance diameter. Our results suggested the important influence of pollinator‐mediated selection on floral evolution. Variations in pollinator assemblages not only resulted in variation in the direction of selection but also the strength of selection on floral traits.     

Between‐year changes in community composition shape species’ roles in an Arctic plant–pollinator network

Inter‐annual turnover in community composition can affect the richness and functioning of ecological communities. If incoming and outgoing species do not interact with the same partners, ecological functions such as pollination may be disrupted. Here, we explore the extent to which turnover affects species’ roles – as defined based on their participation in different motifs positions – in a series of temporally replicated plant–pollinator networks from high‐Arctic Zackenberg, Greenland. We observed substantial turnover in the plant and pollinator assemblages, combined with significant variation in species’ roles between networks. Variation in the roles of plants and pollinators tended to increase with the amount of community turnover, although a negative interaction between turnover in the plant and pollinator assemblages complicated this trend for the roles of pollinators. This suggests that increasing turnover in the future will result in changes to the roles of plants and likely those of pollinators. These changing roles may in turn affect the functioning or stability of this pollination network.     

A theory of the spatial and temporal dynamics of plant communities

An individual-based model of plant competition for light that uses a definition of plant functional types based on adaptations for the simultaneous use of water and light can reproduce the fundamental spatial and temporal patterns of plant communities. This model shows that succession and zonation result from the same basic processes. Succession is interpreted as a temporal shift in species dominance, primarily in response to autogenic changes in light availability. Zonation is interpreted as a spatial shift in species dominance, primarily in response to the effect of allogenic changes in water availability on the dynamics of competition for light. Patterns of succession at different points along a moisture gradient can be used to examine changes in the ecological roles of various functional types, as well as to address questions of shifts in patterns of resource use through time.Our model is based on the cost-benefit concept that plant adaptations for the simultaneous use of two or more resources are limited by physiological and life history constraints. Three general sets of adaptive constraints produce inverse correlations in the ability of plants to efficiently use (1) light at both high and low availability, (2) water at both high and low availability, and (3) both water and light at low availabilities.The results of this type of individual-based model can be aggregated to examine phenomena at several levels of system organization (i.e., subdisciplines of ecology), including (1) plant growth responses over a range of environmental conditions, (2) population dynamics and size structure, (3) experimental and field observations on the distribution of species across environmental gradients, (4) studies of successional pattern, (5) plant physiognomy and community structure across environmental gradients, and (6) nutrient cycling.     

Syrphid flies suppress lettuce aphids

Syrphid flies are abundant in lettuce fields, where their larvae are key predators of aphids. However, the presence of predators in the field does not always result in economically significant levels of prey suppression. Even when predators are numerous, their effects on prey population dynamics may be variable. Over a two year period we surveyed lettuce fields in coastal California, USA to test whether syrphid flies are capable of colonizing fields with aphids and suppressing aphid population growth. The survey showed that female syrphids oviposited more eggs at locations with more aphids, and that greater numbers of syrphid larvae resulted in lower rates of increase in the aphid populations. We also directly manipulated syrphid densities by adding syrphid eggs to uncaged lettuce plants, and these syrphid additions resulted in lower aphid population growth. This research shows that syrphid flies have the ability to suppress aphid populations in lettuce fields.     

Climate mediates roles of pollinator species in plant–pollinator networks

Aim

Understanding how climate conditions influence plant–pollinator interactions at the global scale is crucial to understand how pollinator communities and ecosystem function respond to environmental change. Here, we investigate whether climate drives differences in network roles of the main insect pollinator orders: Diptera, Coleoptera, Lepidoptera and Hymenoptera.

Location

Global.

Time period

1968–2020.

Major taxa studied

Diptera, Coleoptera, Lepidoptera and Hymenoptera.

Methods

We collated plant–pollinator networks from 26 countries and territories across the five main Köppen–Geiger climate zones. In total, we compiled data from 101 networks that included >1500 plant species from 167 families and >2800 pollinator species from 163 families. We assessed differences in the composition of plant–pollinator interactions among climate zones using a permutational ANOVA. We calculated standard network metrics for pollinator taxonomic groups and used Bayesian generalized mixed models to test whether climate zone influenced the proportion of pollinator network links and the level of pollinator generalism.

Results

We found that climate is a strong driver of compositional dissimilarities between plant–pollinator interactions. Relative to other taxa, bees and flies made up the greatest proportion of network links across climate zones. When network size was accounted for, bees were the most generalist pollinator group in the tropics, whereas non-bee Hymenoptera were the most generalist in arid zones, and syrphid flies were the most generalist in polar networks.

Main conclusions

We provide empirical evidence at the global scale that climate strongly influences the roles of different pollinator taxa within networks. Importantly, non-bee taxa, particularly flies, play central network roles across most climate zones, despite often being overlooked in pollination research and conservation. Our results identify the need for greater understanding of how global environmental change affects plant–pollinator interactions.     

Dual invasion analysis: a general model of novel ecological dynamics due to Bt product and resistant pests in wild settings

Transgenic Bt crops have been integrated as a central component of the agricultural policies of many nations across the globe due to their insecticidal properties. While focus on increased yield resulting from the use of Bt crops has overshadowed the concerns of pest populations developing resistance, resistance has been recently discovered in even highly managed fields. One issue that has received less attention is the resulting set of ecological dynamics from escaped Bt products into wild settings. I present a differential equation model of the ecological interaction between a wild plant–pest community and an invading Bt toxin-producing plant and the ensuing evolution of pest resistance. Key to this model investigation is the assumption of energy costs with both the production of Bt toxin by Bt plants and the resistance to Bt toxin exhibited by resistant pest individuals. Results show that persistence of the initial invading Bt plant population is possible through an intransitive loop dynamic. Furthermore, coexistence of wild-type plants and pests as well as Bt-producing plants and resistant pests is possible through the dynamics resultant from energy trade-offs.     

Neutral biogeography of phylogenetically structured interaction networks

Little is known about how biogeographic processes affect the dynamics of species interactions in space and time, although it is widely accepted that they drive community assemblage. In functional interactions, such as pollination and seed dispersal, species that share common ancestry tend to retain a common number of interactions and interact with similar sets of species, a pattern more commonly observed for animals than plants. On the one hand, the most coherent explanation for the phylogenetic structure of pollination and seed dispersal networks is that species retain ecological traits over evolution, which would cause the conservation of interaction partners. On the other hand, fundamental processes of biodiversity, such as dispersal and evolutionary rates seem to have important roles shaping the observed phylogenetic structure of mutualistic networks, but no model has been created to study the effect of these processes in the phylogenetic structure of mutualistic interactions. Here, we developed a stochastic simulation model to study the evolution of two interacting groups of species, which evolve independently over the same geographical domain. In our model, individuals of the same interaction group share ecological traits, whereas individuals of different trophic groups are ecologically distinct. We show that even in the absence of ecological differences between individuals, and disregarding any conservation of phenotypical and phenological traits between species, the interplay of dispersal and speciation is still a major driver of complex phylogenetic structure of functional interactions, such as pollination and seed dispersal.     

Weaving animal temperament into food webs: implications for biodiversity

Recent studies into community level dynamics are revealing processes and patterns that underpin the biodiversity and complexity of natural ecosystems. Theoretical food webs have suggested that species‐rich and highly complex communities are inherently unstable, but incorporating certain characteristics of empirical communities, such as allometric body size scaling and non‐random interaction distributions, have been shown to enhance stability and facilitate species coexistence. Incorporating individual level traits and variability into food web theory is seen as a future pathway for this research and our growing knowledge of individual behaviours, in the form of temperament (or personality) traits, can inform the direction of this research. Temperament traits are consistent differences in behaviour between individuals, which are repeatable across time and/or across ecological contexts, such as aggressive or boldness behaviours that commonly differ between individuals of the same species. These traits, under the framework of behavioural reaction norms, show both individual consistency as well as contextual and phenotypic plasticity. This is likely to contribute significantly to the effects of individual trait variability and adaptive trophic behaviour on the structure and dynamics of food webs, which are apparently stabilizing. Exploring the role of temperament in the context of community ecology is a unique opportunity for cross‐pollination between ecological fields, and can provide new insights into community stability and biodiversity.     

Role of bacteria in the oviposition behaviour and larval development of stable flies

Stable flies, Stomoxys calcitrans (L.), are the most important pests of cattle in the United States. However, adequate management strategies for stable flies, especially for pastured cattle, are lacking. Microbial/symbiont-based approaches offer novel venues for management of insect pests and/or vector-borne human and animal pathogens. Unfortunately, the fundamental knowledge of stable fly-microbial associations and their effect on stable fly biology is lacking. In this study, stable flies laid greater numbers of eggs on a substrate with an active microbial community (> 95% of total eggs oviposited) than on a sterilized substrate. In addition, stable fly larvae could not develop in a sterilized natural or artificial substrate/medium. Bacteria were isolated and identified from a natural stable fly oviposition/developmental habitat and their individual effect on stable fly oviposition response and larval development was evaluated in laboratory bioassays. Of nine bacterial strains evaluated in the oviposition bioassays, Citrobacter freundii stimulated oviposition to the greatest extent. C. freundii also sustained stable fly development, but to a lesser degree than Serratia fanticola. Serratia marcescens and Aeromonas spp. neither stimulated oviposition nor supported stable fly development. These results demonstrate a stable fly bacterial symbiosis; stable fly larval development depends on a live microbial community in the natural habitat, and stable fly females are capable of selecting an oviposition site based on the microbially derived stimuli that indicate the suitability of the substrate for larval development. This study shows a promising starting point for exploiting stable fly-bacterial associations for development of novel approaches for stable fly management.     

Maintenance of temporal synchrony between syrphid flies and floral resources despite differential phenological responses to climate

Variation in species’ responses to abiotic phenological cues under climate change may cause changes in temporal overlap among interacting taxa, with potential demographic consequences. Here, we examine associations between the abiotic environment and plant–pollinator phenological synchrony using a long‐term syrphid fly–flowering phenology dataset (1992–2011). Degree‐days above freezing, precipitation, and timing of snow melt were investigated as predictors of phenology. Syrphids generally emerge after flowering onset and end their activity before the end of flowering. Neither flowering nor syrphid phenology has changed significantly over our 20‐year record, consistent with a lack of directional change in climate variables over the same time frame. Instead we document interannual variability in the abiotic environment and phenology. Timing of snow melt was the best predictor of flowering onset and syrphid emergence. Snow melt and degree‐days were the best predictors of the end of flowering, whereas degree‐days and precipitation best predicted the end of the syrphid period. Flowering advanced at a faster rate than syrphids in response to both advancing snow melt and increasing temperature. Different rates of phenological advancements resulted in more days of temporal overlap between the flower–syrphid community in years of early snow melt because of extended activity periods. Phenological synchrony at the community level is therefore likely to be maintained for some time, even under advancing snow melt conditions that are evident over longer term records at our site. These results show that interacting taxa may respond to different phenological cues and to the same cues at different rates but still maintain phenological synchrony over a range of abiotic conditions. However, our results also indicate that some individual plant species may overlap with the syrphid community for fewer days under continued climate change. This highlights the role of interannual variation in these flower–syrphid interactions and shows that species‐level responses can differ from community‐level responses in nonintuitive ways.     

Variation in the reproductive performance of the Trollius–Chiastocheta mutualism at the edge of its range in north-east Germany

Empirical studies into obligate pollination mutualisms which elucidate the variation in reproductive performance of shrinking populations within human-altered environments are rare. This study focuses on the obligate pollination mutualism between Trollius europaeus (Ranunculaceae) and fly species of the genus Chiastocheta which act both as the plant’s main pollinators and as predators in that their larvae eat a fraction of the developing seeds. The study area is situated in the lowlands of north-east Germany. Many populations of T. europaeus have become comparatively small and scattered in this region as a consequence of agricultural land use intensification. We studied the plant’s reproductive fitness in populations ranging in size from 7 to 12,000 flowers. In a field experiment, we applied four pollination treatments and also recorded fly density in 28 natural T. europaeus populations. The fitness of the offspring from 19 populations was studied in a common garden experiment. In both approaches, a reduction in the fitness of small host plant populations could be demonstrated. Fitness loss can be put down to the quantitative and qualitative limitation of pollen caused by inbreeding and the negative feedback on relative seed set caused by the reduced ability of small plant populations to support a sufficiently large fly population. Although increases in fly density are associated with rising predation costs, the plant species’ net benefit is a positive function of its population size. Our study highlights the reproductive variability of the Trollius–Chiastocheta interaction along a population size gradient in a marginal region of its range, thus contributing to the understanding of the overall variability of this mutualism.     

Pollination context alters female advantage in gynodioecious Silene vulgaris

Gynodioecy, the co‐occurrence of females and hermaphrodites, is arguably the most common angiosperm gender polymorphism in many florae. Females’ ability to invade and persist among hermaphrodites depends, in part, on pollinators providing adequate pollination to females. We directly measured diurnal and nocturnal pollinators’ contributions to female and hermaphrodite seed production in artificial populations of gynodioecious Silene vulgaris by experimentally restricting pollinator access. We found that female relative seed production in this system depended strongly on pollination context: females produced more than twice as many seeds as hermaphrodites in the context of abundant, nectar‐collecting moths. Conversely, females showed no seed production advantage in the context of pollen‐collecting syrphid flies and bees due to acutely hermaphrodite‐biased visitation. We infer that variation in pollinator type, behaviour and abundance may be important for achieving the female relative fitness thresholds necessary for the maintenance of gynodioecy. Generally, our study illustrates how pollinator‐mediated mechanisms may influence the evolution of breeding systems and associated suites of floral traits. Segments of a pollinator community may facilitate gynodioecy by selecting for plant characteristics that increase the attractiveness of both sexes to pollinators, such as nectar rewards. Conversely, discriminating visitors in search of pollen may restrict gynodioecy in associated plant lineages by reducing male steriles’ fitness below threshold levels.     

Patterns of species co-occurrence and density compensation: a test for interspecific competition in bat ectoparasite infracommunities

Parasites constitute an ideal system with which to investigate patterns and mechanisms of community structure and dynamics. Nevertheless, despite their prevalence in natural systems, parasites have been examined less often than other organisms traditionally used for testing hypotheses of community assembly. In the present study, we investigate possible effects of competitive interactions on patterns of distribution (co‐occurrence) and density among a group of streblid bat flies parasitic on short‐tailed fruit bats, Carollia perspicillata. Using null model analyses of species co‐occurrence, we did not find evidence that competition affects the distribution of bat fly species across hosts. Moreover, when non‐infested hosts were included, analyses showed evidence for interspecific aggregation, rather than for the segregation predicted by competition theory. Partial Pearson correlations among bat fly species densities showed no evidence of negative covariation in two of three cases. In the species pair for which a significant negative correlation was found, a visual analysis of plotted covariation indicated a constraint line, suggesting that competition between these two species might become operational only in some infracommunities when abundances of bat flies approach a maximum set by one or more limiting resources. Moreover, when a community‐wide estimation of the significance of density compensation was calculated, the result was not significant. Overall, we find no evidence that competition influences the distribution of bat flies on their hosts, and mixed support for effects of competition on the densities of species. These results are consistent with the idea that competition plays a role in structuring natural communities, but in many systems its effects are context‐dependent and might not be important relative to other factors. Wider analyses across taxonomic and environmental gradients and a detailed consideration of the different hypothesized effects of competition are necessary to fully understand the importance of competition on natural communities.