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Eusociality as a neglected aspect of wild bee α-diversity and its potential impact on diversity estimation
Abstract
1. Bees provide important ecosystem services and are subjects of extensive studies on their α-diversity, which is generally calculated with indices that integrate the number of species with their abundances. Variation in social behaviour, though expected to impact genetic diversity, is still largely neglected in such studies. 2. We propose a simple method to show how sociality may affect diversity indices, when a surrogate of genetic diversity is taken into account. This method weighs the number of sampled females (N) to obtain new abundance values (N W), by taking into account relevant biological traits affecting genetic structure of populations, that is, the number of (natal) nests from which the sampled females originated (which depends on brood productivity and sex ratio) and the genetic relatedness among such females. 3. Solitary species tend to have greater N W than eusocial ones especially at larger sample sizes. Across studies on 121 bee communities, we found that Taxonomic dis-tinctness, Shannon-Wiener diversity and Gini-Simpson dominance tended to be greater when based on N W rather than on N. Such differences increased in communities with decreasing number of eusocial species and with increasing proportion of individuals from eusocial species. 4. The results suggest that taking into account the social organisation of wild bees may have important consequences in estimating α-diversity, thus claiming for future efforts in collecting biological data on as many wild bee species as possible to improve the precision of N W estimations. For example, stressors affecting more solitary bees could impoverish communities dominated by few but abundant eusocial species, more than expected by using unweighted abundances.
Supplementary resources (11)
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Pollinator conservation is aided by knowledge of dispersal behavior, which shapes gene flow and population structure. In many bees, dispersal is thought to be male-biased, and males’ movements may be critical to maintaining gene flow in disturbed and fragmented habitats. Yet male bee movements are challenging to track directly and male dispersal ability remains poorly understood in most species. Here, we combine field manipulations and models to assess male dispersal ability in a stingless bee (Tetragonula carbonaria). We placed colonies with virgin queens at varying distances apart (1–48 km), genotyped the males that gathered at mating aggregations outside each colony, and used pairwise sibship assignment to determine the distribution of likely brothers across aggregations. We then compared simulations of male dispersal to our observed distributions and found best-fit models when males dispersed an average of 2–3 km (>2-fold female flight ranges), and maximum of 20 km (30-fold female flight ranges). Our data supports the view that male bee dispersal can facilitate gene flow over long-distances, and thus play a key role in bee populations’ resilience to habitat loss and fragmentation. In addition, we show that the number of families contributing to male aggregations can be used to estimate local stingless bee colony densities, allowing population monitoring of these important tropical pollinators.
Extensively managed and flower-rich mountain hay meadows, hotspots of Europe's biodiversity, are subject to environmental and climatic gradients linked to altitude. While the shift of pollinators from bee-to fly-dominated communities with increasing elevation across vegetation zones is well established, the effect of highland altitudinal gradients on the community structure of pollinators within a specific habitat is poorly understood. We assessed wild bee and hoverfly communities, and their pollination service to three plant species common in mountain hay meadows, in eighteen extensively managed yellow oat grasslands (Trisetum flavescens) with an altitudinal gradient spanning approx. 300 m. Species richness and abundance of pollinators increased with elevation, but no shift between hoverflies and wild bees (mainly bumblebees) occurred. Seedset of the woodland cranesbill (Geranium sylvaticum) increased with hoverfly abundance, and seedset of the marsh thistle (Cirsium palustre) increased with wild bee abundance. Black rampion (Phyteuma nigrum) showed no significant response. The assignment of specific pollinator communities and their response to altitude in highlands, to different plant species underlines the importance of wild bees and hoverflies as pollinators in extensive grassland systems.
Although ecological disturbances can have a strong influence on pollinators through changes in habitat, virtually no studies have quantified how characteristics of wildfire influence the demography of essential pollinators. Nevertheless, evaluating this topic is critical for understanding how wildfire is linked to pollinator population dynamics, particularly given recent changes in wildfire frequency and severity in many regions of the world. In this study, we measured the demographic response of the blue orchard bee (Osmia lignaria) across a natural gradient of wildfire severity to assess how variation in wildfire characteristics influenced reproductive output, offspring sex ratio, and offspring mass. We placed nest blocks with a standardized number and sex ratio of pre-emergent adult bees across the wildfire gradient, finding some evidence for a positive but highly variable relationship between reproductive output and fire severity surrounding the nest site at both local (100 m) and landscape (750 m) scales. In addition, the production of female offspring was > 10% greater at nest sites experiencing the greatest landscape-scale fire severity relative to the lowest-severity areas. The finding that blue orchard bees biased offspring production towards the more expensive offspring sex with increasing fire severity shows a functional response to changes in habitat quality through increased density of flowering plants. Our findings indicate that burned mixed-conifer forest provides forage for the blue orchard bee across a severity gradient, and that the increase in floral resources that follows high-severity fire leads females to shift resource allocation to the more costly sex when nesting.
In eusocial Hymenoptera, queens and their helper offspring should favour different sex investment ratios. Queens should prefer a 1:1 investment ratio, as they are equally related to offspring of both sexes (r = 0.5). In contrast, helpers should favour an investment ratio of 3:1 towards the production of female brood. This conflict arises because helpers are more closely related to full sisters (r = 0.75) than brothers (r = 0.25). However, helpers should invest relatively more in male brood if relatedness asymmetry within their colony is reduced. This can occur due to queen replacement after colony orphaning, multiple paternity and the presence of unrelated alien helpers. We analysed an unprecedentedly large number of colonies (n = 109) from a UK population of Lasioglossum malachurum, an obligate eusocial sweat bee, to tease apart the effects of these factors on colony-level investment ratios. We found that multiple paternity, unrelated alien helpers and colony orphaning were all common. Queen-right colonies invested relatively more in females than did orphaned colonies, producing a split sex ratio. However, investment ratios did not change due to multiple paternity or the presence of alien helpers, reducing inclusive fitness pay-offs for helpers. Queen control may also have been important: helpers rarely laid male eggs, and investment in female brood was lower when queens were large relative to their helpers. Genetic relatedness between helpers and the brood that they rear was 0.43 in one year and 0.37 in another year, suggesting that ecological benefits, as well as relatedness benefits, are necessary for the maintenance of helping behaviour.
Significance statement
How helping behaviour is maintained in eusocial species is a key topic in evolutionary biology. Colony-level sex investment ratio changes in response to relatedness asymmetries can dramatically influence inclusive fitness benefits for helpers in eusocial Hymenoptera. The extent to which helpers in primitively eusocial colonies can respond adaptively to different sources of variation in relatedness asymmetry is unclear. Using data from 109 colonies of the sweat bee Lasioglossum malachurum, we found that queen loss, but not multiple paternity or the presence of alien helpers, was correlated with colony sex investment ratios. Moreover, we quantified average helper-brood genetic relatedness to test whether it is higher than that predicted under solitary reproduction (r = 0.5). Values equal to and below r = 0.5 suggest that relatedness benefits alone cannot explain the maintenance of helping behaviour. Ecological benefits of group living and/or coercion must also contribute.
Evolution has been viewed as occurring primarily through selection among individuals. We present a framework based on multilevel selection for evaluating evolutionary change from individuals to communities, with supporting empirical evidence. Essential to this evaluation is the role that interspecific indirect genetic effects play in shaping community organization, in generating variation among community phenotypes, and in creating community heritability. If communities vary in phenotype, and those phenotypes are heritable and subject to selection at multiple levels, then a community view of evolution must be merged with mainstream evolutionary theory. Rapid environmental change during the Anthropocene will require a better understanding of these evolutionary processes, especially selection acting at the community level, which has the potential to eliminate whole communities while favoring others.
Expected final online publication date for the Annual Review of Ecology, Evolution, and Systematics, Volume 51 is November 2, 2020. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
Context
Landscape and local habitat traits moderate wild bee communities. However, whether landscape effects differ between local habitat types is largely unknown.
Objectives
We explored the way that wild bee communities in three distinct habitats are shaped by landscape composition and the availability of flowering plants by evaluating divergences in response patterns between habitats.
Methods
In a large-scale monitoring project across 20 research areas, wild bee data were collected on three habitats: near-natural grassland, established flower plantings and residual habitats (e.g. field margins). Additionally, landscape composition was mapped around the research areas.
Results
Our monitoring produced a dataset of 27,650 bees belonging to 324 species. Bee communities on all three habitats reacted similarly to local flower availability. Intensively managed grassland in the surrounding landscape had an overall negative effect on the studied habitats. Other landscape variables produced diverging response patterns that were particularly pronounced during early and late season. Bee communities in near-natural grassland showed a strong positive response to ruderal areas. Flower plantings and residual habitats such as field margins showed a pronounced positive response to extensively managed grassland and woodland edges. Response patterns regarding bee abundance were consistent with those found for species richness.
Conclusion
We advise the consideration of local habitat type and seasonality when assessing the effect of landscape context on bee communities. A reduction in the intensity of grassland management enhances bee diversity in a broad range of habitats. Moreover, wild bee communities are promoted by habitat types such as ruderal areas or woodland edges.
Urbanization is one of the major threats to wild plants and pollinators, and its global increase demands a better understanding of the mechanism driving its negative impact. Urban warming and altered local environmental conditions have the potential to affect the timing of flowering and of pollinator activity. While previous evidence has shown that plant phenology tends to advance in urban areas, little is known about its effects on pollinator phenology. In this study we simultaneously assessed the response of the timing of flowering of native plants and of the flight period of wild pollinators to increased urbanization. We collected data from 12 sites along an urbanization gradient in Northern France, a region under strong anthropogenic pressure. Overall, we recorded more than 70 plant species, and we sampled more than 4300 wild bees and hoverflies belonging to 154 species. Plant flowering showed a strong response to urbanization at the community level with a striking advancement of the flowering peak in sites at high urbanization. On the contrary, pollinator communities did not show any clear shift of their flight phenology along the gradient, neither regarding abundance nor diversity. Our results indicate that phenologies of plant and pollinator communities can respond differently along the same urbanization gradient. These asymmetric responses can drive modifications in the structure of plant–pollinator networks, and potentially negatively affect the fitness of both mutualistic partners.
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Background
The Shannon diversity index has been widely used in population genetics studies. Recently, it was proposed as a unifying measure of diversity at different levels—from genes and populations to whole species and ecosystems. The index, however, was proven to be negatively biased at small sample sizes. Modifications to the original Shannon’s formula have been proposed to obtain an unbiased estimator.
Methods
In this study, the performance of four different estimators of Shannon index—the original Shannon’s formula and those of Zahl, Chao and Shen and Chao et al.—was tested on simulated microsatellite data. Both the simulation and analysis of the results were performed in the R language environment. A new R function was created for the calculation of all four indices from the genind data format.
Results
Sample size dependence was detected in all the estimators analysed; however, the deviation from parametric values was substantially smaller in the derived measures than in the original Shannon’s formula. Error rate was negatively associated with population heterozygosity. Comparisons among loci showed that fast-mutating loci were less affected by the error, except for the original Shannon’s estimator which, in the smallest sample, was more strongly affected by loci with a higher number of alleles. The Zahl and Chao et al. estimators performed notably better than the original Shannon’s formula.
Conclusion
The results of this study show that the original Shannon index should no longer be used as a measure of genetic diversity and should be replaced by Zahl’s unbiased estimator.
Bees require suitably close foraging and nesting sites to minimize travel time and energy expenditure for brood provisioning. Knowing foraging distances in persistent (‘healthy’) populations is therefore crucial for assessing harmful levels of habitat fragmentation. For small bees, such distances are poorly known because of the difficulty of individual tagging and problems with mark-recapture approaches. Using apiarist’s number tags and colour codes, we marked 2689 males and females of four oligolectic and two polylectic species of Osmiini bees (Megachilidae, genera Chelostoma , Heriades , Hoplitis , Osmia ) with body lengths of 6 to 15 mm. The work was carried out in 21 ha-large urban garden that harbours at least 106 species of wild bees. Based on 450 re-sightings, mean female flight distances ranged from 73 to 121 m and male distances from 59 to 100 m. These foraging distances suggest that as a rule of thumb, flower strips and nesting sites for supporting small solitary bees should be no further than 150 m apart.
A functional ecological understanding of urban wild bee communities is of growing importance especially in regard to biodiversity conservation, ecosystem service maintenance and effective conservation programmes. In this paper, we review and summarize the published literature aiming to inform future research investigations in the growing field of wild bee functional ecology. Specifically, we: (1) review which functional trait-based analyses have been carried out on wild bees in cities thus far; (2) summarize which wild bee species traits have been considered; (3) evaluate any consistent wild bee trait–environment relationships (i.e. urbanization) across studies; and (4) synthesize findings and limitations to inform future research recommendations. We reviewed 48 studies based on a systematic Web of Knowledge search. We found consistent trait characteristics for ‘nesting type’, ‘diet’, ‘body size’, ‘sociality’ and ‘phenology’ across studies. More than one third of the studies were descriptive and the majority of studies were located in urban gardens in temperate Europe and North America, calling for more research from underrepresented geographic regions and from the entire spectrum of urban habitat types. Of these studies, only five analyzed functional diversity indices and three studies applied statistics to relate urban wild bee traits to urbanization factors. Future studies should consider trait-based statistics, and could incorporate functional trait-based ecological networks to examine network shifts across urbanization gradients. Our review suggests that we lack generalizable information about wild bee trait and urbanization relationships yet, making conservation recommendations challenging. Therefore, we propose more research that considers methodological recommendations to develop a comparable and comprehensive understanding of how urbanization affects the functional ecology of urban wild bees to link with specific urban conservation measures.
Honey bees are key agricultural pollinators, but beekeepers continually suffer high annual colony losses owing to a number of environmental stressors, including inadequate nutrition, pressures from parasites and pathogens, and exposure to a wide variety of pesticides. In this review, we examine how two such stressors, pesticides and viruses, may interact in additive or synergistic ways to affect honey bee health. Despite what appears to be a straightforward comparison, there is a dearth of studies examining this issue likely owing to the complexity of such interactions. Such complexities include the wide array of pesticide chemical classes with different modes of actions, the coupling of many bee viruses with ectoparasitic Varroa mites, and the intricate social structure of honey bee colonies. Together, these issues pose a challenge to researchers examining the effects pesticide-virus interactions at both the individual and colony level.
Increasing temperatures and declines
One aspect of climate change is an increasing number of days with extreme heat. Soroye et al. analyzed a large dataset of bumble bee occurrences across North America and Europe and found that an increasing frequency of unusually hot days is increasing local extinction rates, reducing colonization and site occupancy, and decreasing species richness within a region, independent of land-use change or condition (see the Perspective by Bridle and van Rensburg). As average temperatures continue to rise, bumble bees may be faced with an untenable increase in frequency of extreme temperatures.
Science , this issue p. 685 ; see also p. 626
An added-variable plot is an effective way to show the correlation between an independent variable and a dependent variable conditional on other independent variables. For multivariate estimation, a simple scatterplot showing x versus y is not adequate to show the partial correlation of x with y, because it ignores the impact of the other covariates. Added-variable plots are especially effective for showing the correlation of a dummy x variable with y because the dummy variable conditional on other covariates becomes a continuous variable, making the relationship easier to visualize.
Added-variable plots are also useful for spotting influential outliers in the data that affect the estimated regression parameters. Stata provides added-variable plots after ordinary least-squares regressions with the avplot command. I present a new command, avciplot, that adds a confidence interval and other options to the avplot command.
The Asian hornet is an invasive predator of honey bees in Western Europe. The Asian hornet-related risk of bee colony mortality has motivated the development of biological and physical control methods over the past years. Although the technical cost-benefit ratio has been established for most of these control methods, it is still unclear whether such methods can reduce the detrimental effects of the Asian hornet on European honey bees. In this study, we investigated the potential benefits of a biodiversity-friendly control method, the beehive muzzle. We observed the flight activity of bees and the predation behaviour of the Asian hornets at the beehive entrance of 22 pairs of honey bee colonies, each with one muzzle-equipped colony and one control colony without muzzle, in France. We measured HF (bee homing failure due to hornet predation of bees) and FP (foraging paralysis: the stop of flight activity in beehives due to hovering hornets), and estimated the mortality probability of the colonies using a mechanistic modelling approach. The beehive muzzle did not reduce the hornet-related HF, but drastically reduced FP. Moreover, the muzzle increased the survival probability of hornet-stressed colonies up to 51% in context of high abundance of Asian hornets based on theoretical simulations. These results suggest that installing beehive muzzles can mitigate the detrimental effect of the Asian hornet on European honey bees. This low-cost technique does not lead to any environmental impacts and could therefore be recommended to beekeepers as an effective biodiversity-friendly method of Asian hornet control.
Background
Intraspecific variation in foraging niche can drive food web dynamics and ecosystem processes. In particular, male and female animals can exhibit different, often cascading, impacts on their interaction partners. Despite this, studies of plant-pollinator interaction networks have focused on the partitioning of the floral community between pollinator species, with little attention paid to intraspecific variation in plant preference between male and female bees. We designed a field study to evaluate the strength and prevalence of sexually dimorphic foraging, and particularly resource preferences, in bees.
Study design
We observed bees visiting flowers in semi-natural meadows in New Jersey, USA. To detect differences in flower use against a shared background of resource (flower) availability, we maximized the number of interactions observed within narrow spatio-temporal windows. To distinguish observed differences in bee use of flower species, which can reflect abundance patterns and sampling effects, from underlying differences in bee preferences, we analyzed our data with both a permutation-based null model and random effects models.
Findings
We found that the diets of male and female bees of the same species were often dissimilar as the diets of different species of bees. Furthermore, we demonstrate differences in preference between male and female bees. We show that intraspecific differences in preference can be robustly identified among hundreds of unique species-species interactions, without precisely quantifying resource availability, and despite high phenological turnover of both bees and plant bloom. Given the large differences in both flower use and preferences between male and female bees, ecological sex differences should be integrated into studies of bee demography, plant pollination, and coevolutionary relationships between flowers and insects.
Agricultural intensification is a major driver of wild bee decline. Vineyards may be inhabited by plant and animal species, especially when the inter‐row space is vegetated with spontaneous vegetation or cover crops. Wild bees depend on floral resources and suitable nesting sites which may be found in vineyard inter‐rows or in viticultural landscapes. Inter‐row vegetation is managed by mulching, tillage, and/or herbicide application and results in habitat degradation when applied intensively. Here, we hypothesize that lower vegetation management intensities, higher floral resources, and landscape diversity affect wild bee diversity and abundance dependent on their functional traits. We sampled wild bees semi‐quantitatively in 63 vineyards representing different vegetation management intensities across Europe in 2016. A proxy for floral resource availability was based on visual flower cover estimations. Management intensity was assessed by vegetation cover (%) twice a year per vineyard. The Shannon Landscape Diversity Index was used as a proxy for landscape diversity within a 750 m radius around each vineyard center point. Wild bee communities were clustered by country. At the country level, between 20 and 64 wild bee species were identified. Increased floral resource availability and extensive vegetation management both affected wild bee diversity and abundance in vineyards strongly positively. Increased landscape diversity had a small positive effect on wild bee diversity but compensated for the negative effect of low floral resource availability by increasing eusocial bee abundance. We conclude that wild bee diversity and abundance in vineyards is efficiently promoted by increasing floral resources and reducing vegetation management frequency. High landscape diversity further compensates for low floral resources in vineyards and increases pollinating insect abundance in viticulture landscapes.
Wild bees are indispensable pollinators, supporting global agricultural yield and angiosperm biodiversity. They are experiencing widespread declines, resulting from multiple interacting factors. The effects of urbanization, a major driver of ecological change, on bee populations are not well understood. Studies examining the aggregate response of wild bee abundance and diversity to urbanization tend to document minor changes. However, the use of aggregate metrics may mask trends in particular functional groups. We surveyed bee communities along an urban-to-rural gradient in SE Michigan, USA, and document a large change in observed sex ratio (OSR) along this gradient. OSR became more male biased as urbanization increased, mainly driven by a decline in medium and large bodied ground-nesting female bees. Nest site preference and body size mediated the effects of urbanization on OSR. Our results suggest that previously documented negative effects of urbanization on ground-nesting bees may underestimate the full impact of urbanization, and highlight the need for improved understanding of sex-based differences in the provision of pollination services by wild bees.
The emergence of eusociality represents a major evolutionary transition from solitary to group reproduction. The most commonly studied eusocial species, honey bees and ants, represent the behavioral extremes of social evolution but lack close relatives that are non-social. Unlike these species, the halictid bee Lasioglossum albipes produces both solitary and eusocial nests and this intraspecific variation has a genetic basis. Here, we identify genetic variants associated with this polymorphism, including one located in the intron of syntaxin 1a (syx1a), a gene that mediates synaptic vesicle release. We show that this variant can alter gene expression in a pattern consistent with differences between social and solitary bees. Surprisingly, syx1a and several other genes associated with sociality in L. albipes have also been implicated in autism spectrum disorder in humans. Thus, genes underlying behavioral variation in L. albipes may also shape social behaviors across a wide range of taxa, including humans.
Overall, 9.2% of bees are considered threatened in all of Europe, while at the EU 27 level, 9.1% are threatened with extinction. A further 5.2% and 5.4% of bees are considered Near Threatened in Europe and the EU 27, respectively (101 species at both levels). However, for 1,101 species (56.7%) in Europe and 1,048 species (55.6%) at the EU 27, there was not enough scientific information to evaluate their risk of extinction and thus, they were classified as Data Deficient. When more data become available, many of these might prove to be threatened as well.
Looking at the population trends of European bee species, 7.7% (150 species) of the species have declining populations, 12.6% (244 species) are more or less stable and 0.7% (13 species) are increasing. The population trends for 1,535 species (79%) remains unknown.
A high proportion of threatened bee species are endemic to either Europe (20.4%, 400 species) or the EU 27 (14.6%, 277 species), highlighting the responsibility that European countries have to protect the global populations of these species. Almost 30% of all the species threatened (Critically Endangered, Endangered, or Vulnerable) at the European level are endemic to Europe (e.g., found nowhere else in the world).
The species richness of bees increases from north to south in Europe, with the highest species richness being found in the Mediterranean climate zone. In particular, the Iberian, Italian and Balkan peninsulas are important areas of species richness. Regarding the distribution of
endemic species, southern Europe shows the highest concentration of endemism. The largest numbers of threatened species are located in south-central Europe and the pattern of distribution of Data Deficient species is primarily concentrated in the Mediterranean region.
The main threat to European bees is habitat loss as a result of agriculture intensification (e.g., changes in agricultural practices including the use of pesticides and fertilisers), urban development, increased frequency of fires and climate change.
Greater social complexity at lower latitudes has been observed in a variety of arthropods from termites to spiders. Social behavior in the small carpenter bees, Ceratina, has been shown to vary widely both between species and across geographic range. Our goal was to determine how social plasticity of three populations of Ceratina species, C. calcarata and C. strenua, vary across a latitudinal gradient. The longer rearing season in the south did not result in two separate brood rearing periods, but instead increased brood production of a single brood with a higher female sex bias. The social structure of nests remained stable across both species’ ranges: mothers exhibit prolonged parental care and worker dwarf eldest daughters occur among populations and species. This is the first report of worker daughters in C. strenua. The ubiquity of worker daughter production in eastern North American Ceratina suggests that factors outside of climate underlie the early division of labor between the reproductive mother and worker dwarf eldest daughter.
Green roofs are potentially valuable habitats for plants and animals in urban areas. Wild bees are important pollinators for crops and wild plants and may be enhanced by anthropogenic structures, but little is known about wild bees on green roofs in cities. This study investigates the effects of green roof qualities (floral resources, substrate character and depth, roof height and age) on wild bee diversity, abundance and traits (nesting type, sociality, pollen specialisation, body size) on green roofs in Vienna. Nine green roofs were sampled monthly between March and September 2014 by a semi quantitative approach. Wild bees were collected in pre-defined sub-areas for the same amount of time and floral resources were recorded. Over all green roofs, 992 individuals belonging to 90 wild bee species were observed. Wild bee diversity and abundance was strongly positively affected by increasing forage availability and fine substrates. Wild bees on roofs were characteristically solitary, polylectic and 8.3–11.2 mm. Regarding nesting type, the percentage of above-ground nesting bees was higher compared to the common species composition in Middle Europe. Ground-nesting wild bees were mainly eusocial, smaller (6.4–9.6 mm) and positively affected by roofs with fine substrates. During June, when forage availability by wildflowers on roofs was “low” (5–15% flower coverage), flowering Sedum species were an important forage resource. We conclude that wild bee diversity and abundance on green roofs are enhanced by floral resources. Furthermore, the installations of areas with finer and deeper substrates benefit ground nesting and eusocial wild bees.
Understanding how plant diversity influences higher trophic levels is important for predicting the consequences of global biodiversity loss. While early studies have focused on the effects of plant species richness, more recently a growing number of experiments have explored the effects of plant intraspecific diversity by manipulating the genotypic richness of plant communities. 2.By combining 162 estimates of effect size from 60 experimental studies, we examined the effects of plant genotypic richness on arthropods, one of the most diverse and abundant taxa which play a crucial role in many ecosystem processes and services. We have also compared the effects of plant genetic and species diversity on arthropods when both were manipulated within the same study. 3.Species richness and abundance of most trophic groups of arthropods was higher in genetically diverse plant stands. Interestingly, the effects of plant genetic diversity on natural enemies of herbivores were stronger than the effects of plant genetic diversity on herbivores, suggesting that plant genetic diversity effects on predators might be driven by mechanisms independent of herbivores. 4.Herbivore and predator abundance increased with plant genetic diversity in studies using wild plants whereas predator abundance was unaffected and herbivore abundance was reduced by crop genetic diversity. Damage by generalist herbivores was reduced by plant genetic diversity whereas damage by specialist herbivores was not affected. 5.When the effects of plant genetic and species diversity on arthropods were compared within the same study, the magnitude of plant genetic diversity effects was comparable to that of plant species diversity. 6.Our results suggest that plant genetic diversity has significant effects on the diversity of arthropods across several trophic levels, thus highlighting the importance of maintaining high levels of both plant species and genetic diversity for arthropod conservation. However, the potential of using crop genetic mixtures in agriculture for pest control appears to be limited as even though herbivore abundance was reduced in genetically diverse plots, herbivore damage and predator abundance were not affected by crop genotypic richness. This article is protected by copyright. All rights reserved.
Annual insects are predicted to grow larger where the growing season is longer. However, transitions from one to two generations per year can occur when the season becomes sufficiently long, and are predicted to result in a sharp decrease in body size because available development time is halved. The potential for resulting saw-tooth clines has been investigated only in solitary taxa with free-living larvae. 2. Size clines were investigated in two socially polymorphic sweat bees (Halictidae): transitions between solitary and social nesting occur along gradients of increasing season length, characterised by the absence or presence of workers and offspring that are individually mass provisioned by adults. How the body size changes with season length was examined, and whether transitions in social phenotype generate saw-tooth size clines. We measured Lasioglossum calceatum and Halictus rubicundus nest foundresses originating from more than 1000 km of latitude, encompassing the transition between social and solitary nesting. 3. Using satellite-collected temperature data to estimate season length, it was shown that both species were largest where the season was longest. Body size increased linearly with season length in L. calceatum and non-linearly in H. rubicundus but the existence of saw-tooth clines was not supported. 4. The present results suggest that because the amount of food consumed by offspring during development is determined by adults, environmental and social influences on the provisioning strategies of adult bees may be more important factors than available feeding time in determining offspring body size in socially polymorphic sweat bees.
Intraspecific variation is a major component of biodiversity, yet it has received relatively little attention from governmental and non-governmental organizations, especially with regard to conservation plans and the management of wild species. This omission is ill-advised because phenotypic and genetic variation within and among populations can have dramatic effects on ecological and evolutionary processes, including responses to environmental change, the maintenance of species diversity, and ecological stability and resilience. At the same time, environmental changes associated with many human activities, such as land-use and climate change, have dramatic and often negative impacts on intraspecific variation. We argue for the need for local, regional, and global programs to monitor intraspecific genetic variation. We suggest that such monitoring should include two main strategies: (1) intensive monitoring of multiple types of genetic variation in selected species; and (2) broad-brush modeling for representative species for predicting changes in variation as a function of changes in population size, range extent, and connectivity. Overall, we call for collaborative efforts to initiate the urgently needed monitoring of intraspecific variation. This article is protected by copyright. All rights reserved.
Given the predicted expansion of cities throughout the world, understanding the effect of urbanization on bee fauna is a major issue for the conservation of bees. The aim of this study was to understand how urbanization affects wild bee assemblages along a gradient of impervious surfaces and to determine the influence of landscape composition and floral resource availability on these assemblages. We chose 12 sites with a proportion of impervious surfaces (soil covered by parking, roads, and buildings) ranging from 0.06% to 64.31% within a 500 m radius. We collected using pan trapping and estimated the landscape composition of the sites within a 500 m radius and the species richness of plant assemblages within a 200 m radius. We collected 1104 bees from 74 species. The proportion of impervious surfaces at the landscape scale had a negative effect on wild bee abundance and species richness, whereas local flower composition had no effect. Ground-nesting bees were particularly sensitive to the urbanization gradient. This study provides new evidences of the impact of urbanization on bee assemblages and the proportion of impervious surfaces at the landscape scale emerged as a key factor that drives those assemblages.
1. Bumble bees are important eusocial pollinators whose worker caste, fuelled by nectar sugar, accelerate colony growth through brood incubation, but allocating workers to nectar foraging could compromise nest thermoregulation in daytime and produce ‘incubator limitation’.
2. We hypothesise that colonies in nectar‐poor habitats experience stronger incubator limitation by diverting workers from incubation to foraging, but this potential effect of habitat quality on colony fitness via task allocation is not fully understood.
3. We therefore modelled levels of nectar foraging in relation to forage richness and theoretically estimated the impact of incubator‐limitation on colony fitness. Additionally, we investigated whether live colonies of bumble bees (Bombus terrestris) responded to manipulation of their sugar supply as if incubator‐limited.
4. Model solutions for environmentally realistic scenarios showed that colonies allocate up to one third of workers to nectar foraging in order to avoid sugar starvation during sustained incubation. The incubator‐limitation that results can strongly reduce colony reproduction, but its impact depends on the temperature regime of the nesting habitat.
5. Live colonies allocated between one sixth and one third of daytime worker effort to foraging and responded to sugar supplementation as if incubator‐limited.
6. These findings suggest that forage richness and nest temperature relations could interact to affect the fitness of wild bumble bee colonies through incubator limitation. Our testable theory promises an integrative understanding of how forage quality and climate could govern the distribution and abundance of bumble bees and other eusocial insects that utilise brood incubation by their worker caste.
How do social insects expand and adapt to new ranges and how does sociality per se contribute to their success (or failure)? These questions can become tractable with the use of population genomics. We explored the population genomics of the socially polymorphic small carpenter bee, Ceratina australensis, across its range in eastern and southern Australia to search for evidence of selection and identify loci associated with social nesting. We sampled and sequenced fully the genomes of 54 socially and solitarily nesting C. australensis within Queensland, Victoria and South Australia, yielding 2 061 234 single nucleotide polymorphisms across the genome. We found strong evidence of population-specific selection and evidence of genetic variants associated with social nesting behaviour. Both the sets of associated loci and differentially expressed ‘social’ genes had evidence of positive selection, suggesting that alleles at genes associated with social nesting might provide different fitness benefits.
Habitat loss and edge effects resulting from habitat fragmentation are key processes implicated in the decline of bee populations globally. Their effects on wild bees and their pollination services in natural ecosystems are poorly understood, particularly in North American prairies. Our objectives were to determine whether natural habitat loss and edge effects affect bee abundance and pollination services in the Northern Great Plains. We sampled bee abundance and pollination services along transects beginning at road or tree edges in grasslands located in Manitoba, Canada. We measured bee abundance using pan traps, and pollination services using seed-set of Brassica rapa (L.) (Brassicales: Brassicaceae) phytometers. We collected local-scale habitat data by measuring occurrence of flowering species, vegetation type, and vegetation structure, and we measured habitat amount at 1-km radii using GIS analysis of landscape cover. Increasing amounts of habitat loss resulted in declines in bee abundance, and sometimes in pollination services. Results varied with bee life-history: proximity to road edges negatively affected social bees, and litter depth had negative effects on below- ground-nesting bees. Surprisingly, few effects on bees led to corresponding impacts on pollination services. This suggests that conservation of intact natural habitat across the northern Great Plains is important for maintaining resilient and diverse bee communities, but that efforts to conserve bee populations cannot be assumed to also maintain all associated pollination services.
Pollinators of most of the plants cultivated in the Mediterranean regions of Europe are still unknown. We provide new data and we review previously available information on bees (Apoidea) associated with three economically important crops in Spain: melon (Cucumis melo L.), watermelon (Citrullus lanatus (Thunb.) Matsum. & Nakai) and almond (Prunus dulcis (Mill.) D.A.Webb). We found that, overall, 98 bee species spanning four families visit flowers of the studied crop species, and 46 additional species were sampled within the crops with pan-traps. The bee assemblages visiting melon include 7-33 species, with moderate to high importance of small Lasioglossum (Halictidae) and of honey bee (Apis mellifera Linnaeus, 1758: Apidae), and in one case of small Ceratina: Apidae. Watermelon flowers are visited by 11-14 species of bees, with highest abundance of honey bees or of small Lasioglossum, depending on the locality. Bees collected on almond trees included 12-37 species, with the honey bee and medium-size to large Andrena (Andrenidae) and Osmia (Megachilidae) being predominant. The new samples expanded the geographical distributions of nearly one-fourth of the collected species. Diversity estimators slightly varied even within fields of the same crop, and a cluster analysis suggested both a certain overlap between melon and watermelon and a role of geographical distance on similarity among bee assemblages, though these patterns were much clearer using presence data rather than abundances. Below-ground-nesting and solitary species were more frequently collected than above-ground-nesting and eusocial species, but for melon and watermelon the highest abundances were recorded for eusocial species. Almost exclusively polylectic species visited the flowers of the three studied crops. The results of this study could help in planning conservation actions to maintain this important diversity of potential pollinators in Spanish areas covered by these crops.
Stingless bees (Meliponini) are the largest and most diverse group of social bees, yet their largely tropical distribution means that they are less studied than their relatives, the bumble bees and honey bees. Stingless bees produce honey and collect pollen from tens of thousands of tropical plant species and, in the process, provide critical pollination services in the tropics. Like many other insects, they are struggling with new human-made challenges like habitat destruction, climate change and new diseases.
This book provides an overview of stingless bee biology, with chapters on the evolutionary history, nesting biology, colony organisation and division of labour of stingless bees. In addition, it explores their defence strategies, foraging ecology, and varied communication methods. Accordingly, the book offers an accessible introduction and reference guide for students, researchers and laypeople interested in the biology of bees.
• About 3/4 of all wild bee species nest in the soil and spend much of their life cycle underground. These insects require suitable environmental conditions for nest construction and for the development and survival of their offspring. However, there is little quantitative information on the nesting habitat requirements and preferences of ground‐nesting bees. Moreover, there are almost no data on the effects of nesting conditions on these bees' fitness.
• Here, to better understand the factors that influence nest‐site selection in ground‐nesting bees, we synthesise the literature on the nesting‐habitat associations of these important pollinators. We also review techniques that can be used to study the nesting preferences of ground‐nesting bees.
• Our review reveals enormous variation among bee species in their associations with such nesting‐habitat attributes as soil texture, compaction, moisture, temperature, ground surface features, and proximity to conspecifics or floral resources. However, more studies—particularly experimental ones—are needed to segregate the influence of each factor on bees' choices of nesting location, since multiple factors are often correlated. It is also unclear whether nesting‐habitat associations vary geographically or seasonally within species, or phylogenetically among ground‐nesting bee species, partly because we lack information on nesting habitat for many species.
• We argue that studies using established habitat‐selection methods are essential to properly identify nesting‐habitat preferences of ground‐nesting species. Finally, more research on nesting ecology is needed (especially in agroecosystems) to determine how best to support this diverse group of bees and the vital ecosystem service they provide.
en Land‐use intensification for agricultural purposes modifies the structure of natural environments in various ways and at different spatial scales. These modifications can affect ecological processes and the community structure of multi‐environment users such as solitary bees and wasps. Understanding the role of distinct habitat descriptors in promoting such changes is one of the major challenges of empirical studies. In this study, we use a multi‐scale approach to evaluate how landscape compositional and configurational heterogeneity, vegetation structural complexity, and the proportion of agricultural landscape composition affect communities of bees and wasps that nest in pre‐existing cavities in remnants of native vegetation bordering agroecosystems. We selected 25 sampling points along a gradient of amount of surrounding agriculture and landscape diversity within natural physiognomies located in Chapada Diamantina, Bahia, Brazil. Through model selection using Akaike's information criterion, we verified the complementary roles of landscape heterogeneity and local vegetation in structuring these hymenopteran communities. Abundance in the groups showed different tendencies depending on the descriptors employed, pointing to the importance of evaluating within‐group specificity. Furthermore, bees and wasps presented differential responses to landscape composition, but they did not differ in relation to configurational complexity. In more heterogeneous landscapes or sites with more complex local vegetation, the proportion of agriculture had a positive influence on the response evaluated. Efficient management of agricultural landscapes therefore requires increased landscape heterogeneity and conservation or restoration of native vegetation remnants at the local scale.
Resumo
pt A intensificação do uso do solo para fins agrícolas modifica a estrutura dos ambientes naturais de várias maneiras e em diferentes escalas espaciais. Essas modificações podem afetar processos ecológicos e a estrutura das comunidades de animais que usam múltiplos hábitats, como abelhas e vespas solitárias. Compreender o papel das variáveis que descrevem o hábitat na mudança da estrutura das comunidades é um dos principais desafios dos estudos empíricos. Neste estudo, usamos uma abordagem em várias escalas espaciais para avaliar como a heterogeneidade da composição e da configuração da paisagem, a proporção de agricultura, bem como a complexidade estrutural da vegetação afetam comunidades de abelhas e vespas que nidificam em cavidades pré‐existentes em remanescentes de vegetação nativa em agroecossistemas. Foram selecionados 25 pontos amostrais ao longo de um gradiente de proporção de agricultura e diversidade da paisagem em fitofisionomias naturais localizadas na Chapada Diamantina, Bahia, Brasil. Através da seleção de modelos usando o Critério de Informação de Akaike (AIC), verificamos os papéis complementares da heterogeneidade da paisagem e vegetação local na estruturação dessas comunidades de himenópteros. A abundância nos grupos mostrou tendências diferentes dependendo dos descritores empregados, apontando a importância de avaliar a especificidade dentro do grupo. Além disso, abelhas e vespas apresentaram respostas diferentes à composição da paisagem, mas não diferiram em relação à complexidade da configuração. Em paisagens mais heterogêneas ou locais com vegetação local mais complexa, a proporção da agricultura teve uma influência positiva na resposta avaliada. Portanto, o manejo eficiente de paisagens agrícolas requer maior heterogeneidade da paisagem e conservação ou restauração de remanescentes de vegetação nativa em escala local.
Urban areas are growing worldwide and alter landscapes in a persistent fashion, thereby affecting biodiversity and ecosystem services such as pollination in a little understood way. Here we present a systematic review of the peer-reviewed literature to identify the drivers of urban pollinator populations and pollination. A total of 141 studies were reviewed and qualitatively analyzed. Pollinator responses to urbanization were contrasting. We contend that positive responses were often associated with urban sprawl, i.e. moderate levels of urbanization of rural, mostly agricultural land below 50% impervious surface, whereas high levels of densification with high percentages of sealed and built-up area (above 50%), largely led to pollinator declines and loss of pollination services. Further, urbanization generally reduced pollinator diversity when compared to natural or semi-natural areas, but enhanced it when compared to intensified agricultural landscapes. In addition, pollinator responses were commonly highly trait-and scale-specic. Cavity nesters and generalist species usually profited more from urbanization than ground nesters and specialists. Overall, urban pollinator communities still seem to provide sufficient pollination services to wild vegetation and crops. Pollinator diversity generally increased with the amount of urban green spaces at the landscape scale, and locally with availability of nesting resources and flowering plants. Positive effects of floral additions were largely independent of the plant's origin, whether native or non-native. Only a few studies included landscape configuration. Likewise, abiotic urban drivers, e.g. heat island effects and air and light pollution, remain little studied. Tropical and developing regions, most heavily impacted by current and future urbanization, are strongly underrepresented. We conclude that biodiversity friendly urbanization can make a valuable contribution to pollinator conservation, in particular in face of the continued intensification of rural agriculture.
When animals become sick, infected cells and an armada of activated immune cells attempt to eliminate the pathogen from the body. Once infectious particles have breached the body's physical barriers of the skin or gut lining, an initially local response quickly escalates into a systemic response, attracting mobile immune cells to the site of infection. These cells complement the initial, unspecific defense with a more specialized, targeted response. This can also provide long-term immune memory and protection against future infection. The cell-autonomous defenses of the infected cells are thus aided by the actions of recruited immune cells. These specialized cells are the most mobile cells in the body, constantly patrolling through the otherwise static tissue to detect incoming pathogens. Such constant immune surveillance means infections are noticed immediately and can be rapidly cleared from the body. Some immune cells also remove infected cells that have succumbed to infection. All this prevents pathogen replication and spread to healthy tissues. Although this may involve the sacrifice of some somatic tissue, this is typically replaced quickly. Particular care is, however, given to the reproductive organs, which should always remain disease free (immune privilege).
A diverse array of wild bee species may provide more effective pollination than the widely employed European honey bee (Apis mellifera L.). High species richness within crop pollinator assemblages has been linked to enhanced fruit and seed yields, but species richness is often confounded with abundance in studies of pollinator communities. We investigated the effects of bee diversity and species identity on pollen deposition and crop yield in the strawberry (Fragaria x ananassa) variety Jewel through a field experiment that independently manipulated the species richness and abundance of flower visitors. We used a new pollen deposition measurement technique to determine the pollen contribution of individual bees in an assemblage of flower visits. We compared the performance of wild bee species and managed honey bees, as pollinators of strawberry. We also calculated the influence of species richness, visit frequency, and visitor identity on fruit mass, using the fruit that developed from each sampled flower. Species richness of flower visitors did not influence floral pollen loads or strawberry mass. Honey bees and wild bees deposited the same amount of pollen per visited flower. However, strawberries that developed from flowers visited by wild bees were heavier than flowers visited by honey bees. In addition, flowers visited by a combination of wild and honey bees produced strawberries that weighed less than flowers receiving purely wild bee visits. Synthesis and applications. Our findings show that honey bee pollination results in lower yields than wild bee pollination in a strawberry crop. Consequently, if managed honey bees in strawberry fields displace wild pollinators, growers may obtain suboptimal yields. Management efforts aimed at the maintenance or enhancement of wild pollinator populations may therefore be a cost‐effective way to increase both crop yield and biodiversity on strawberry farms. This article is protected by copyright. All rights reserved.
Understanding the relationships between biodiversity and ecosystem functioning has major implications. Biodiversity–ecosystem functioning relationships are generally investigated at the interspecific level, although intraspecific diversity (i.e. within‐species diversity) is increasingly perceived as an important ecological facet of biodiversity. Here, we provide a quantitative and integrative synthesis testing, across diverse plant and animal species, whether intraspecific diversity is a major driver of community dynamics and ecosystem functioning. We specifically tested (i) whether the number of genotypes/phenotypes (i.e. intraspecific richness) or the specific identity of genotypes/phenotypes (i.e. intraspecific variation) in populations modulate the structure of communities and the functioning of ecosystems, (ii) whether the ecological effects of intraspecific richness and variation are strong in magnitude, and (iii) whether these effects vary among taxonomic groups and ecological responses. We found a non‐linear relationship between intraspecific richness and community and ecosystem dynamics that follows a saturating curve shape, as observed for biodiversity–function relationships measured at the interspecific level. Importantly, intraspecific richness modulated ecological dynamics with a magnitude that was equal to that previously reported for interspecific richness. Our results further confirm, based on a database containing more than 50 species, that intraspecific variation also has substantial effects on ecological dynamics. We demonstrated that the effects of intraspecific variation are twice as high as expected by chance, and that they might have been underestimated previously. Finally, we found that the ecological effects of intraspecific variation are not homogeneous and are actually stronger when intraspecific variation is manipulated in primary producers than in consumer species, and when they are measured at the ecosystem rather than at the community level. Overall, we demonstrated that the two facets of intraspecific diversity (richness and variation) can both strongly affect community and ecosystem dynamics, which reveals the pivotal role of within‐species biodiversity for understanding ecological dynamics.
Darwin famously described special difficulties in explaining social evolution in insects. More than a century later, the evolution of sociality - defined broadly as cooperative group living - remains one of the most intriguing problems in biology. Providing a unique perspective on the study of social evolution, this volume synthesizes the features of animal social life across the principle taxonomic groups in which sociality has evolved. The chapters explore sociality in a range of species, from ants to primates, highlighting key natural and life history data and providing a comparative view across animal societies. In establishing a single framework for a common, trait-based approach towards social synthesis, this volume will enable graduate students and investigators new to the field to systematically compare taxonomic groups and reinvigorate comparative approaches to studying animal social evolution.
Background:
In recent years, concern has been raised over honey bee colony losses, and also among wild bees there is evidence for extinctions and range contractions in Europe and North America. Pesticides have been proposed as a potential cause of this decline. Bees are exposed simultaneously to variety of agrochemicals, which may cause synergistically detrimental impacts, which are incompletely understood. We investigated the toxicity of the fungicide imazalil in mixture with four common insecticides: fipronil (phenylpyrazoid); cypermethrin (pyrethroid); thiamethoxam; and imidacloprid (neonicotinoids). EBI fungicides like imazalil can inhibit P450 detoxification systems in insects and therefore fungicide-insecticide co-occurrence might produce synergistic toxicity in bees. We assessed the impact of dietary fungicide-insecticide mixtures on the mortality and feeding rates of laboratory bumble bees (Bombus terrestris L.).
Results:
Regarding mortality, imazalil synergised the toxicity of fipronil, cypermethrin and thiamethoxam, but not imidacloprid. We found no synergistic effects on feeding rates.
Conclusion:
Our findings suggest that P450-based detoxification processes are differentially important in mitigating the toxicity of certain insecticides, even those of the same chemical class. Our evidence that cocktail effects can arise in bumble bees should extend concern over the potential impacts of agrochemical mixtures to include wild bee species in farmland.
Pollinator conservation is of increasing interest in light of managed honeybee (Apis mellifera) declines, and declines in some species of wild bees. Much work has gone into understanding the effects of habitat enhancements in agricultural systems on wild bee abundance, richness, and pollination services. However, the effects of ecological restoration targeting “natural” ecological endpoints (e.g., restoring former agricultural fields to historic vegetation types or improving degraded natural lands) on wild bees have received relatively little attention, despite their potential importance for countering habitat loss. 2.We conducted a meta-analysis to evaluate the effects of ecological restoration on wild bee abundance and richness, focusing on unmanaged bee communities in lands restored and managed to increase habitat availability and quality. Specifically, we assessed bee abundance and/or richness across studies comparing restored vs. unrestored treatments and studies investigating effects of specific habitat restoration techniques, such as burning, grazing, invasive plant removal and seeding. 3.We analysed 28 studies that met our selection criteria: these represented 11 habitat types and 7 restoration techniques. Nearly all restorations associated with these studies were performed without explicit consideration of habitat needs for bees or other pollinators. The majority of restorations targeted plant community goals, which could potentially have ancillary benefits for bees. 4.Restoration had overall positive effects on wild bee abundance and richness across multiple habitat types. Specific restoration actions, tested independently, also tended to have positive effects on wild bee richness and abundance. 5.Synthesis and applications. We found strong evidence that ecological restoration advances wild bee conservation. This is important given that habitat loss is recognized as a leading factor in pollinator decline. Pollinator responses to land management are rarely evaluated in non-agricultural settings and so support for wild bees may be an underappreciated benefit of botanically focused management. Future restoration projects that explicitly consider the needs of wild bees could be more effective at providing nesting, foraging and other habitat resources. We encourage land managers to design and evaluate restoration projects with the habitat needs of wild bee species in mind. This article is protected by copyright. All rights reserved.
Phylogenetic diversity indices are widely used to characterize the structure and diversity of ecological communities. Most indices are based on a metric that is expected to vary with species richness, so they are standardized to remove this richness‐dependence. With this standardization, values of 0 are consistent with random phylogenetic structure, while phylogenetic clustering is associated with either negative or positive values (depending on the index). One common interpretation of phylogenetic clustering is that it indicates some combination of environmental and biological filtering that restricts the species that can be present in a community. Increasingly, studies are comparing phylogenetic indices along environmental gradients to infer differences in the factors structuring communities. This comparison implicitly assumes that index values are comparable among communities with different numbers of species.
Using a set of simulations, I show here that this assumption is incorrect. Holding the strength of filtering constant, communities composed of more species show larger absolute index values. This problem is most pronounced when the environmental filter favors a moderate‐sized clade strongly over others and when using the net relatedness index (NRI) to measure clustering. This bias potentially casts doubt on studies studying phylogenetic index patterns along gradients where richness also varies. Fortunately, the arising generality that more stressful environments have lower species richness and stronger clustering is opposite to this bias and therefore robust. I also show that a simple rarefaction can remove the richness‐dependence of these indices, at the expense of increased error.
Bee populations are declining in the industrialized world, raising concerns for the sustainable pollination of crops. Pesticides, pollutants, parasites, diseases, and malnutrition have all been linked to this problem. We consider here neurobiological, ecological, and evolutionary reasons why bees are particularly vulnerable to these environmental stressors. Central-place foraging on flowers demands advanced capacities of learning, memory, and navigation. However, even at low intensity levels, many stressors damage the bee brain, disrupting key cognitive functions needed for effective foraging, with dramatic consequences for brood development and colony survival. We discuss how understanding the relationships between the actions of stressors on the nervous system, individual cognitive impairments, and colony decline can inform constructive interventions to sustain bee populations.
Wild and managed pollinators provide a wide range of benefits to society in terms of contributions to food security, farmer and beekeeper livelihoods, social and cultural values, as well as the maintenance of wider biodiversity and ecosystem stability. Pollinators face numerous threats, including changes in land-use and management intensity, climate change, pesticides and genetically modified crops, pollinator management and pathogens, and invasive alien species. There are well-documented declines in some wild and managed pollinators in several regions of the world. However, many effective policy and management responses can be implemented to safeguard pollinators and sustain pollination services.
Overwintered gynes establish haplometrotic nests in spring. A single brood of workers is produced in the northern region; two broods are common in C Europe and S Spain; up to three broods occur in some parts of the Mediterranean area. Nests in the first phase contain 3-12 cells, arranged in a comb and surrounded by a cavity. Nests of later phases are deeper with increasing numbers of cells. The caste system is based on conspicuous morphometric and physiological differences. Gynes are reared on big pollen balls, and required a diapause before nest foundation in spring. Queens lay virtually all diploid eggs for worker and gyne production. Workers are raised on small provisions, lack a diapause, but commence activities immediately after emergence. Their main tasks include foraging, defence and construction. Males acount for only 2% of the first brood, but their numbers increase throughout the summer. Populations of nests in the last phase can range from a handful to close to 90 bees. Productivity is commensurate, exending from a low of half a dozen gynes to more than several hundred sexuals. Fecundity of this magnitude explains the colonising efficacy of the species, both with regards to newly created nest sites and old aggregations recently devastated by the depredations of brood parasites. -from Author