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Habitat preference influences response to changing agricultural landscapes in two long-horned bees
Journal of Apicultural Research
Abstract
Agricultural intensification and urban development have drastically influenced pollinators living in semi-natural grasslands. Pollinators are likely to have different responses to more intensive land uses; some decline rapidly, whereas others maintain or increase their populations. We predicted that differences in interspecific responses to different land uses are partly attributed to differences in habitat preference. We examined the distribution and flower use patterns of two closely related Eucera species with different habitat preferences. Study sites were narrow belt-like meadows within traditional, intensified, and urbanised agricultural lands in the Osaka-Kobe metropolitan area, Japan. Forest-associated Eucera nipponensis were significantly fewer in consolidated and urbanised meadows than in traditional meadows, whereas open land-associated E. spurcatipes exhibited the opposite pattern. A significant negative relationship between their abundance was also found. Both species foraged on legume flowers most frequently (83.5%), but their floral use patterns differed significantly in traditional and consolidated meadows. The bee species that preferred stable habitats were vulnerable to land consolidation and urbanisation, while the species associated with disturbed habitats maintained or increased its population size in meadows with these intensive land uses. Thus, recent land-use changes may have different impacts on species with different habitat preferences.
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In response to the qualitative and quantitative changes in floral resources, bumble bees flexibly forage multiple plant species throughout the growing season. During the short summer in an alpine ecosystem, the activity of worker bees is maximized in the middle of the season, when the competition for floral resources may be intense. We predicted that the foraging patterns of bumble bees are affected by both relative floral abundance and interactions between bumble bee species. We recorded the floral abundance of individual plant species and the foraging frequency of bumble bees in an alpine meadow during the major flowering period over 3 years. Two bumble bee species were common during the major flowering period. Although they tended to visit abundant floral species, the shorter-tongued species (Bombus hypocrita) showed a more diverse and flexible floral choice than the longer-tongued species (Bombus beaticola). The degree of floral use overlap between two bumble bee species tended to decrease when the foraging density of the longer-tongued species was high. These results indicated that multiple bumble bee species are able to coexist when certain bee species can flexibly change targeting flowers in response to the temporal variations in flowering species and the density of competing bee species. The extent of foraging flexibility is related to the morphological traits of bee species and availability of floral resources.
Flowers on the ground of orchards can provide substantial resources for wild pollinators of orchard trees. Few studies, however, have examined the relative importance of groundcover flowers to orchard pollination by analyzing pollen on the body surface of pollinators. Oriental persimmon trees bloom within the longer blooming period of white clover, which is occasionally found as a flowering plant on the ground of persimmon orchards in Japan. The present study compared the insect species assemblage collected on persimmon flowers with that on clover. Before persimmon bloomed, Bombus ardens ardens and Apis cerana japonica were the major visitors of clover flowers. Once persimmon bloomed, the former was the most abundant bee that visited persimmon flowers over the flowering period. Apis mellifera was captured only on clover flowers. We found numerous clover pollen grains on the body surface of bumblebees captured on persimmon flowers, but far fewer persimmon pollen grains on bees that visited clover. These findings show that B. ardens ardens utilized the clover flowers under the orchards before persimmon bloomed. Before persimmon bloomed, Bombus ardens ardens and Apis cerana japonica were the major visitors of clover flowers. Once persimmon bloomed, the former was the most abundant bee that visited persimmon flowers over the flowering period. It was suggested that this bumblebee utilized the clover flowers under the orchards before persimmon bloomed.
Rewardless plants use various strategies to attract pollinators. Generalized food-deceptive species exploit the nonspecific food-seeking responses of their pollinators. Because past experiences are important for establishing the food-seeking behaviors of insects, previous flower visits by pollinators should play crucial roles in rewardless plants. In this study, we investigated previous experiences of insects that visited the rewardless orchid Bletilla striata based on pollen attached to their bodies to clarify whether experience of visiting flowers with similar colors as rewardless flowers is necessary. Contrary to the expectation, less than half of the flower visitors carried pollen of flowers with similar colors as B. striata, implying that past experience is not essential. Furthermore, we investigated the effects of learning based on the association between the flower position and fruit set assuming that the fruit set would decrease with the progression of the flowering season. A significant association was found at only one of the three study sites. Among flower visitors, male long-horned bees (Eucera spurcatipes) and honeybees (Apis mellifera) primarily carried B. striata pollinia. We hypothesize that B. striata uses generalized food deception to attract honeybees and rendezvous attraction to attract mate-searching male long-horned bees and that this mixed strategy invalidates the associations assumed in generalized food deception.
Despite growing concern over consequences of global changes, we still know little about potential interactive effects of anthropogenic perturbations and diversity loss on the stability of local communities, especially for taxa other than plants. Here we analyse the relationships among landscape composition, biodiversity and community stability looking at time series of three types of communities, i.e., bats, birds and butterflies, monitored over the years by citizen science programs in France. We show that urban and intensive agricultural landscapes as well as diversity loss destabilize these communities but in different ways: while diversity loss translates into greater population synchrony, urban and intensive agricultural landscapes mainly decrease mean population stability. In addition to highlight the stabilizing effects of diversity on ecologically important but overlooked taxa, our results further reveal new pathways linking anthropogenic activities to diversity and stability. Environmental change and species diversity could jointly affect the stability of animal communities. Here the authors use citizen science data on bats, birds, and butterflies along urbanization and agricultural intensification gradients in France to show that both environmental change and diversity loss destabilise communities, but in different ways.
The role of urban expansion on bee diversity is poorly understood, but it may play an important role in restructuring pollinator diversity observed in rural regions at the urban perimeter. We studied bee communities in two habitats essential for pollinators (residential gardens and semi-natural areas) at 42 sites situated at the edge of greater Montreal, Canada. Bee species richness, abundance and functional diversity all increased with urbanization in both habitat types, but gardens and semi-natural areas supported distinct bee communities with unique responses to urbanization in terms of species turnover. Compared to semi-natural sites, residential gardens supported bees that foraged from a greater number but a lower proportion of available plant species. Bees did not discriminate between exotic and indigenous plant species in either gardens or semi-natural sites and were attracted to flowers in either habitat irrespective of their origins. Protecting semi-natural ruderal areas and providing residential garden habitats for pollinators are both effective means of promoting regional bee diversity in urbanizing regions.
Functional diversity loss among pollinators has rapidly progressed across the globe and is expected to influence plant–pollinator interactions in natural communities. Although recent findings suggest that the disappearance of a certain pollinator functional group may cause niche expansions and/or shifts in other groups, no study has examined this prediction in natural com- munities with high plant and pollinator diversities. By comparing coastal pollination networks on continental and oceanic islands, we examined how community-level flower visit patterns are influenced by the relative biomass of long-tongued pollinators (RBLP). We found that RBLP significantly corre- lated with pollinator functional diversity and was lower in oceanic than in continental islands. Pollinator niches shifted with decreasing RBLP, such that diverse species with various proboscis lengths, especially short- tongued species, increasingly visited long-tubed flowers. However, we found no conspicuous negative impacts of low RBLP and the consequent niche shifts on pollinator visit frequencies to flowers in oceanic island communities. Notably, fruit set significantly decreased as RBLP decreased in a study plant species. These results suggest that niche shifts by other func- tional groups can generally compensate for a decline in long-tongued pollinators in natural communities, but there may be negative impacts on plant reproduction.
Pollinators are fundamental to maintaining both biodiversity and agricultural productivity, but habitat destruction, loss
of flower resources, and increased use of pesticides are causing declines in their abundance and diversity. Using historical
records, we assessed the rate of extinction of bee and flower-visiting wasp species in Britain from the mid-19th century to
the present. The most rapid phase of extinction appears to be related to changes in agricultural policy and practice beginning
in the 1920s, before the agricultural intensification prompted by the Second World War, often cited as the most important
driver of biodiversity loss in Britain. Slowing of the extinction rate from the 1960s onward may be due to prior loss of the
most sensitive species and/or effective conservation programs.
Land use is known to reduce the diversity of species and complexity of biotic interactions. In theory, interaction networks can be used to predict the sensitivity of species against co‐extinction, but this has rarely been applied to real ecosystems facing variable land‐use impacts. We investigated plant–pollinator networks on 119 grasslands that varied quantitatively in management regime, yielding 25 401 visits by 741 pollinator species on 166 plant species.
Species‐specific plant and pollinator responses to land use were significantly predicted by the weighted average land‐use response of each species' partners. Moreover, more specialized pollinators were more vulnerable than generalists. Both predictions are based on the relative interaction strengths provided by the observed interaction network. Losses in flower and pollinator diversity were linked, and mutual dependence between plants and pollinators accelerates the observed parallel declines in response to land‐use intensification. Our findings confirm that ecological networks help to predict natural community responses to disturbance and possible secondary extinctions.
We review direct and indirect impacts of invasive alien species (focussing on plants and insects) on native bees worldwide.
Although there is a rapidly growing body of research into the effects of invasive alien plants on native plant pollination
via disruption of native mutualisms, there has been little research on the impacts of invasive alien plants directly on bees.
Such impacts are likely to vary according to the taxon of plant, the functional specificity of the native bees, and ecosystem
context. Conversely, there have been more attempts to document impacts of invasive alien social bees on native bees. Most
of these studies only indirectly evaluate competition for resources, have focused on a few native species and findings are
sometimes contradictory. However, some studies showed strong negative impacts, suggesting that effects might be species-specific.
Additionally, pathogen spillover and reproductive disruption due to interspecific mating has been demonstrated among some
closely related taxa. Where we lack unequivocal evidence for impacts however, this should not be interpreted as lack of effect.
We recommend that future studies are robustly designed and consider impacts on genetic, species (particularly solitary bees)
and ecosystem biodiversity.
We describe the richness, abundance, and ecological characteristics of bees in community gardens located in heavily developed neighborhoods of the Bronx and East Harlem, NY. In total, 1,145 individual bees, representing 54 species (13% of the recorded New York State bee fauna) were collected over 4 yr. The nesting habits of these species include bees that nest in cavities (33% of species), hives (11% of species), pith (1.9% of species), wood (1.9% of species), or soft/rotting wood (7.4% of species) substrates. Soil-nesting individuals were relatively rare (25% of individuals), perhaps due to a lack of proper soils for nesting sites. Parasitic species were scarce (5.6% of species, 2.6% of individuals), most likely because of an absence or rarity of host species. Overall, exotic species were abundant and constituted 27% of the total individuals collected and 19% of the identified species. We compare these results to several bee faunal surveys in New Jersey and New York State, including newly reported species lists for Central Park and Prospect Park in New York City. Relative to other studies, bee richness of the urban gardens is reduced and composition is biased toward exotic and cavity-nesting species. Nevertheless, despite their small size and location within highly urbanized areas, urban community gardens harbor a diverse assemblage of bees that may provide pollination services and opportunities for ecological exposure and education.
The pollination of flowering plants by animals represents a critical ecosystem service of great value to humanity, both monetary and otherwise. However, the need for active conservation of pollination interactions is only now being appreciated. Pollination systems are under increasing threat from anthropogenic sources, including fragmentation of habitat, changes in land use, modem agricultural practices, use of chemicals such as pesticides and herbicides, and invasions of non-native plants and animals. Honeybees, which themselves are non-native pollinators on most continents, and which may harm native bees and other pollinators, are nonetheless critically important for crop pollination. Recent declines in honeybee numbers in the United States and Europe bring home the importance of healthy pollination systems, and the need to further develop native bees and other animals as crop pollinators. The 'pollination crisis' that is evident in declines of honeybees and native bees, and in damage to webs of plant-pollinator interaction, may be ameliorated not only by cultivation of a diversity of crop pollinators, but also by changes in habitat use and agricultural practices, species reintroductions and removals, and other means. In addition, ecologists must redouble efforts to study basic aspects of plant-pollinator interactions if optimal management decisions are to be made for conservation of these interactions in natural and agricultural ecosystems.
Recent declines of bee species have led to great interest in preserving and promoting bee populations for agricultural and wild plant pollination. Many correlational studies have examined the indirect effects of factors such as landscape context and land management practices and found great variation in bee response. We focus here on the evidence for effects of direct factors (i.e., food resources, nesting resources, and incidental risks) regulating bee populations and then interpret varied responses to indirect factors through their species-specific and habitat-specific effects on direct factors. We find strong evidence for food resource availability regulating bee populations, but little clear evidence that other direct factors are commonly limiting. We recommend manipulative experiments to illuminate the effects of these different factors. We contend that much of the variation in impact from indirect factors, such as grazing, can be explained by the relationships between indirect factors and floral resource availability based on environmental circumstances.
The world's only intensively managed ground-nesting bee, the alkali bee (Nomia melanderi Cockerell), has been used for 50 years as an effective pollinator of alfalfa (Medicago sativa L.) grown for seed in the western USA. Across a 240 km watershed in Washington, the 24 most populous of 56 nest sites found were annually surveyed for nesting bees for 8 years. Alkali bees multiplied 9-fold to 17 million females, the largest reported metapopulation of non-social bees. Several sites have remained populous for an unprecedented 50 years. The most populous nesting bed (1.5 ha) grew to 5.3 million nesting females (median = 278 nests/m, the largest bee nesting aggregation ever recorded. This first-ever exhaustive landscape-level survey for any non-social bee reveals that even amid intensive conventional agriculture, a native bee can sustainably multiply to vast numbers, its nesting aggregations persisting for decades.
Urban bee ecology is an emerging field that holds promise for advancing knowledge of bee community dynamics and promoting bee conservation. Published studies of bee communities in urban and suburban habitats are fewer than those documenting bees in agricultural and wildland settings. As land lost to urbanization is predicted to increase in coming years the necessity of studying urban bee populations is growing. We reviewed 59 publications on urban bee ecology with the following goals, to assess current knowledge, to highlight areas in need of further research, and to suggest applications of study findings to bee conservation. Identified trends in urban areas included the following, negative correlation between bee species richness and urban development, increase in abundance of cavity-nesters in urban habitats, and scarcity of floral specialists. Future directions for studying urban bee ecology include incorporation of landscape-scale assessments, conducting manipulative experiments and actively designing urban bee habitats.
Despite widespread concern about declines in pollination services, little is known about the patterns of change in most pollinator
assemblages. By studying bee and hoverfly assemblages in Britain and the Netherlands, we found evidence of declines (pre-versus
post-1980) in local bee diversity in both countries; however, divergent trends were observed in hoverflies. Depending on the
assemblage and location, pollinator declines were most frequent in habitat and flower specialists, in univoltine species,
and/or in nonmigrants. In conjunction with this evidence, outcrossing plant species that are reliant on the declining pollinators
have themselves declined relative to other plant species. Taken together, these findings strongly suggest a causal connection
between local extinctions of functionally linked plant and pollinator species.
Traditional farming landscapes in China consist of small irregular fields with an intimately interspersed semi-natural habitat network of field margins, but are increasingly converted into consolidated ones that consist of standardized fields with reduced areas of field margins and other semi-natural habitat. It is unclear how such farmland consolidation influences pollinator communities, and if there is a negative effect, whether this effect is mitigated by semi-natural habitat present in the wider landscape. We compared the diversity and abundance of wild pollinators in oilseed rape fields that were embedded in landscapes that consisted either of traditional or consolidated farmland. The landscapes spanned a range of semi-natural habitat area from 10% to 73% at a scale of one km radius in Jiangxi Province, China. Pollinators were sampled using pan traps during two years (2015 and 2019). Results showed that pollinator diversity was positively associated with the proportion of semi-natural habitat in both traditional and consolidated farming landscapes, but was higher in traditional farming landscapes. In both years, there was no difference in pollinator abundance between landscapes with traditional and consolidated fields. The results indicate that the network of field margins in traditional farmland supports a diverse pollinator community, and that land consolidation has equivalent effects on pollinator diversity as substantial decreases in semi-natural habitat in the wider landscape. The role of semi-natural habitat in supporting farmland biodiversity and its associated services needs therefore to be considered in plans for farmland consolidation.
Male solitary bees typically use emergence‐nesting areas and/or flower patches of food plants, where receptive females are relatively numerous, as rendezvous sites. However, mate‐seeking males have been also observed at food‐deceptive orchid patches, where numerous encounters with foraging females can hardly be expected, owing to the lack of floral rewards. Here, we describe the male mate‐seeking and mating behaviors of the Japanese long‐horned bee Eucera nipponensis at habitats of the food‐deceptive orchid Cymbidium goeringii. On the basis of the results, we report empty flower patches are not necessarily fruitless sites for mate‐seeking males because naive female bees, which are highly likely to be recently emerged and unmated, can be attracted to non‐rewarding orchids. We also suggest a possibility that a small number of the males could receive a “sexual reward” (i.e. mating opportunities), owing to the food‐deceptive orchid, in return for their pollination work. This occasional interaction could represent the initial stage in the evolution of sexually deceptive orchids from food‐deceptive orchids. Male mate‐seeking and mating behaviors of the Japanese long‐horned bee Eucera nipponensis were studied at habitats of the food‐deceptive orchid Cymbidium goeringii. On the basis of the results, we report empty flower patches are not necessarily fruitless sites for mate‐seeking males because naive female bees, which are highly likely to be recently emerged and unmated, can be attracted to non‐rewarding orchids.
Land-use changes cause biodiversity loss in semi-natural ecosystems worldwide. Biotic homogenization has led to biodiversity loss, mainly through declines in species composition turnover. Elucidating patterns of turnover in species composition could enhance our understanding of how anthropogenic activities affect community assembly. Here, we focused on whether the decreasing patterns in plant diversity and turnover of species composition resulting from land-use change vary in two regions. We estimated the species diversity and composition of semi-natural grasslands surrounding paddy fields in satoyama landscapes. We examined the differences in species diversity and composition across three land-use types (abandoned, traditional, and intensified) in two regions (Hyogo and Niigata Prefectures, Japan), which were characterized by different climatic conditions. We then assessed alpha-, beta-, and gamma-diversity to compare the patterns of diversity losses in the two regions as a result of land-use changes. In each region, gamma-diversity was consistently higher in the traditional sites compared to abandoned or intensified sites. The analyses revealed that most of the beta-diversity in traditional sites differed significantly from those of abandoned and intensified sites in both regions. However, the beta-diversity of total and perennial species did not differ between traditional and abandoned sites in the Hyogo region. We noted that the beta-diversity of total and perennial species in intensified sites was much lower than that in the traditional sites of the Niigata region. Overall, the patterns of alpha- and gamma-diversity loss were similar in both study regions. Although the biotic homogenization was caused by intensified land-use in the Niigata region, this hypothesis did not completely explain the loss of biodiversity in the abandoned sites in the Hyogo region. The present study contributes to the growing body of work investigating changes in biodiversity as a result of both biotic homogenization and differentiation in semi-natural ecosystems. Conservationists and policy makers should focus on patterns of species composition responded to land-use changes that continue to increase worldwide.
We briefly review current understanding of wild pollinators and pollination services on farmlands.
We consider how concepts in plant ecology – community assembly and functional trait diversity ‐ may be applied to create diverse, wild pollinator communities across scales in agroecosystems.
We also make recommendations for best practices to enhance pollination services and create more sustainable food production systems under changing environmental conditions, including creating greater landscape connectivity, embracing pollinator dynamics, and providing incentives and other motivations to support these practices.
Synthesis . We highlight the opportunity for agricultural lands to serve a dual role for both food production and pollinator conservation, and conclude by posing unanswered questions and top priorities for future studies.
Plant–pollinator interactions are affected by global change, with largely negative impacts on pollination and plant reproduction. Urban areas provide a unique and productive study system for understanding the impacts of many global change drivers on plant–pollinator interactions.
We review the mechanistic pathways through which urban drivers alter plant–pollinator interactions. The literature on urban drivers of plant–pollinator interactions is small but growing and has already produced exciting insights about how population processes or pollinator behaviour interacts with landscape urban drivers to affect pollination outcomes.
Habitat loss and fragmentation can change flower visitation rates and pollination success through changes in pollinator foraging behaviour or through population‐level effects on pollinators. Urban environments, where impermeable surface provides an inhospitable matrix, may allow researchers to identify habitat fragments more clearly than in many other environments.
Recent studies have found that non‐native plants are not differently preferred by pollinators relative to native plants, therefore removing the basis for expecting pollinator‐mediated competition between native and non‐native plants in urban habitats. However, non‐native species together with managed vegetation may have powerful effects in urban habitats via changes in community‐level plant phenology and consequent changes in pollinator phenology.
The current level of climate warming has not caused plants and pollinators to become detectably temporally separated, although at the same time, diversity among species’ phenological responses could buffer plant–pollinator interactions from climate variation. Due to the urban warming effect, cities provide a promising system for better understanding the warming effects on plant–pollinator interactions.
Environmental contaminants such as soil nitrogen and heavy metal pollution have been examined with respect to plant–pollinator interactions in small‐scale, mechanistic studies. The extent to which environmental contaminants drive plant–pollinator interactions in actual urban landscapes is, however, currently unknown.
Important knowledge gaps that require research attention include understanding the consequences of plant and pollinator trait filtering on plant–pollinator interactions, and expanding the literature to include underrepresented biomes and pollinator taxa.
Declines in plants and herbivorous insects due to land-use abandonment and intensification, have been studied in agricultural areas worldwide. We tested four hypotheses, which were complementary rather than mutually exclusive, to understand the mechanisms driving biodiversity decline due to abandonment and intensification. These predict that biodiversity decline is caused by a decline in resource diversity, changes in disturbance regime, surrounding landscape conversion and a decrease in biomass production. We compared plant richness and butterfly and orthopteran richness and diversity among three land-use types in semi-natural grasslands: abandoned, traditional, and intensified terraces. Then, we examined effects of changes in resource (plant) richness, frequency of disturbance (mowing), and surrounding landscapes on butterfly and orthopteran diversity to understand the mechanisms driving decline after land abandonment and intensification. Plant and herbivore richness and diversity were significantly lower in abandoned and intensified grasslands than in traditional grasslands. This trend was consistent throughout the seasons in both years of study. Changes in mowing frequency and the surrounding landscape explained plant richness decline as a consequence of land abandonment and intensification. Declines in herbivorous insects were explained by plant richness declines and changes in mowing frequency but not by landscape changes. Plant and herbivore richness were maximized at an intermediate mowing frequency (ca. twice per year), which is typical practice on traditional terraces. This is the first report demonstrating that the intermediate disturbance hypothesis well explained the biodiversity declines in agricultural ecosystems. The richness and diversity responses of herbivore functional groups to plant richness, mowing frequency, and surrounding landscapes were generally inconsistent with predictions. We found significant trends in which butterfly and orthopteran species with low abundance in traditional terraces were lost in abandoned and/or intensive terraces. This may suggest that the number of individuals of most herbivorous species decreased randomly with respect to life-history traits following a decline in plant richness after changes in disturbance frequency. This study demonstrates that declines in herbivorous insects can be explained by multiple factors and provides a unified explanation for biodiversity decline in both abandoned and intensified of agricultural lands, which have often been studied separately.
Major drivers of amphibian declines via urbanization include land-use changes that cause loss, fragmentation, splits, and degradation of habitat. The effects of these changes in habitat conditions on the persistence of populations are expected to differ among species depending on their dispersal habits: species with strong site fidelity would likely be more affected by habitat loss and degradation, whereas species with highly dispersive habits would be more threatened by habitat fragmentation and split (the dispersal-dependent-decline hypothesis). To test this hypothesis, we examined the distribution patterns of two paddy-associated frog species (Pelophylax nigromaculatus and Hyla japonica) with different dispersal habits along a rural–urban gradient of the Osaka–Kobe metropolitan area, Japan. Our results partially support the dispersal-dependent-decline hypothesis in that the species with strong site fidelity, i.e., P. nigromaculatus, was threatened by habitat-area (agricultural field) decline and habitat-quality degradation (prevalence of concrete levees) rather than by habitat fragmentation. To the best of our knowledge, our study is the first report that suggests paddy-associated amphibian declines via urbanization in the Asian region. However, the second half of the hypothesis, i.e., that the dispersive species (H. japonica) would be more strongly affected by habitat fragmentation via roads and habitat split via declines in surrounding forests was not supported. The lack of support for this portion of the hypothesis may be due to the high adaptability of H. japonica to artificial landscapes. We discuss the value of the dispersal-dependent-decline hypothesis for conservation planning in agricultural lands of urban areas.
Animals pollinate 87% of the world's flowering plant species. Therefore, how pollinators respond to human-induced land-use change has important implications for plants and the species that depend on them. Here, we syn-thesize the published literature on how land-use change affects the main groups of pollinators: bees, butterflies, flies, birds, and bats. Responses to land-use change are predominantly negative but are highly variable within and across taxa. The directionality of pollinator response varies according to study design, with comparisons across gradients in surrounding land-scape cover finding largely negative responses and comparisons across local land-use types finding largely positive responses. Furthermore, among the studies using landscape designs, most were performed in systems where land-use change is extreme, and such studies find stronger negative effects than those performed in more moderate systems. Across multiple taxa, dietary specialists show greater sensitivity to land use than do generalists. There is a need for studies of pollinator species composition and relative abundance, rather than simply species richness and aggregate abundance, to identify the species that are lost and gained with increasing land-use change.
In intensively farmed agricultural landscapes, many species are confined to very small uncultivated areas such as field margins. However, it has been suggested that these small habitat elements cannot support viable populations of all the species observed there. Instead, species richness and abundance in these small habitat fragments may, at least partly, be dependent on dispersal from larger semi‐natural grassland fragments.
We tested this hypothesis for butterflies and bumble bees in 12 independent landscapes in a region of intense agriculture in southern Sweden. In each landscape we surveyed abundance and species richness in one semi‐natural grassland, one linear habitat (uncultivated field margin) adjacent to this (called proximate) and one similar linear habitat (called distant) situated at least 1000 m from the semi‐natural grassland patch.
Both species richness and density (individuals per unit area) of butterflies and bumble bees were significantly higher in proximate linear habitats than in distant ones. Moreover, butterfly species richness was higher for a given area in grasslands than in any of the linear habitat types. Butterfly density in grasslands did not differ from that in proximate linear habitats but was lower in distant linear habitats. The effect of isolation on density was stronger for less mobile butterfly species. For bumble bees there was no difference in species richness between grasslands and proximate linear habitats.
For at least some of the butterfly species even these relatively small fragments of semi‐natural grasslands act as population sources from which individuals disperse to the surrounding habitats and thereby contribute to higher densities and species richness in adjacent areas. For bumble bees, it is more likely that the grasslands contain a higher density of nests than the surrounding intensively cultivated landscape, and that the density of foraging bumble bees decreases with increasing distance from the nest.
Synthesis and application. Habitat fragmentation and intensified agricultural practices are considered to be a threat against services provided by pollinators. In order to sustain the abundance and diversity of insect pollinators in intensively farmed agricultural landscapes, we suggest that preservation of the remaining semi‐natural grasslands or re‐creation of flower‐rich grasslands is essential.
It is clear that the majority of flowering plants are pollinated by insects and other animals, with a minority utilising abiotic pollen vectors, mainly wind. However there is no accurate published calculation of the proportion of the ca 352 000 species of angiosperms that interact with pollinators. Widely cited figures range from 67% to 96% but these have not been based on firm data. We estimated the number and proportion of flowering plants that are pollinated by animals using published and unpublished community-level surveys of plant pollination systems that recorded whether each species present was pollinated by animals or wind. The proportion of animal-pollinated species rises from a mean of 78% in temperate-zone communities to 94% in tropical communities. By correcting for the latitudinal diversity trend in flowering plants, we estimate the global number and proportion of animal pollinated angiosperms as 308 006, which is 87.5% of the estimated species-level diversity of flowering plants. Given current concerns about the decline in pollinators and the possible resulting impacts on both natural communities and agricultural crops, such estimates are vital to both ecologists and policy makers. Further research is required to assess in detail the absolute dependency of these plants on their pollinators, and how this varies with latitude and community type, but there is no doubt that plant–pollinator interactions play a significant role in maintaining the functional integrity of most terrestrial ecosystems.
Although traditional agricultural land use maintains biodiversity, recent land-use changes involving abandonment or use intensification have rapidly reduced the biodiversity of agricultural landscapes. Organisms living in agricultural landscapes are likely to respond differently to these changes, with some species declining rapidly and others remaining unchanged. However, few studies have focused on this interspecific difference in susceptibility to land abandonment and intensification in agricultural landscapes. We hypothesize that rarer herb species are more susceptible to both abandonment and intensification than are common herbs due to habitat preferences in the semi-natural grasslands of agricultural landscapes. To test this hypothesis, we examined the distributions of two pairs of congeneric grasslands species on abandoned and consolidated (production-intensified) paddy fields to assess differences in vulnerability to paddy abandonment and consolidation between the rarer and the more common species in an agricultural landscape. We found that higher, steeper fields farther from roads in the upper areas of paddy terraces were more frequently abandoned in our study area. The two rarer species had significantly more overlap with the distribution of fields at risk of abandonment than did the two more common congeneric species. In addition, the two rarer species were significantly less widely distributed in consolidated fields. Thus, both land abandonment and intensification appear to asymmetrically decrease habitats of rarer species. In light of our findings, we also discuss biodiversity conservation in agricultural landscapes with changing land use.
The ability to predict the responses of ecological communities and individual species to human-induced environmental change remains a key issue for ecologists and conservation managers alike. Responses are often variable among species within groups making general predictions difficult. One option is to include ecological trait information that might help to disentangle patterns of response and also provide greater understanding of how particular traits link whole clades to their environment. Although this “trait-guild” approach has been used for single disturbances, the importance of particular traits on general responses to multiple disturbances has not been explored. We used a mixed model analysis of 19 data sets from throughout the world to test the effect of ecological and life-history traits on the responses of bee species to different types of anthropogenic environmental change. These changes included habitat loss, fragmentation, agricultural intensification, pesticides and fire. Individual traits significantly affected bee species responses to different disturbances and several traits were broadly predictive among multiple disturbances. The location of nests – above vs. below ground – significantly affected response to habitat loss, agricultural intensification, tillage regime (within agriculture) and fire. Species that nested above ground were on average more negatively affected by isolation from natural habitat and intensive agricultural land use than were species nesting below ground. In contrast below-ground-nesting species were more negatively affected by tilling than were above-ground nesters. The response of different nesting guilds to fire depended on the time since the burn. Social bee species were more strongly affected by isolation from natural habitat and pesticides than were solitary bee species. Surprisingly, body size did not consistently affect species responses, despite its importance in determining many aspects of individuals’ interaction with their environment. Although synergistic interactions among traits remain to be explored, individual traits can be useful in predicting and understanding responses of related species to global change.
Species distributional or trait data based on range map (extent-of-occurrence) or atlas survey data often display spatial autocorrelation, i.e. locations close to each other exhibit more similar values than those further apart. If this pattern remains present in the residuals of a statistical model based on such data, one of the key assumptions of standard statistical analyses, that residuals are independent and identically distributed (i.i.d), is violated. The violation of the assumption of i.i.d. residuals may bias parameter estimates and can increase type I error rates (falsely rejecting the null hypothesis of no effect). While this is increasingly recognised by researchers analysing species distribution data, there is, to our knowledge, no comprehensive overview of the many available spatial statistical methods to take spatial autocorrelation into account in tests of statistical significance. Here, we describe six different statistical approaches to infer correlates of species' distributions, for both presence/absence (binary response) and species abundance data (poisson or normally distributed response), while accounting for spatial autocorrelation in model residuals: autocovariate regression; spatial eigenvector mapping; generalised least squares; (conditional and simultaneous) autoregressive models and generalised estimating equations. A comprehensive comparison of the relative merits of these methods is beyond the scope of this paper. To demonstrate each method's implementation, however, we undertook preliminary tests based on simulated data. These preliminary tests verified that most of the spatial modeling techniques we examined showed good type I error control and precise parameter estimates, at least when confronted with simplistic simulated data containing spatial autocorrelation in the errors. However, we found that for presence/absence data the results and conclusions were very variable between the different methods. This is likely due to the low information content of binary maps. Also, in contrast with previous studies, we found that autocovariate methods consistently underestimated the effects of environmental controls of species distributions. Given their widespread use, in particular for the modelling of species presence/absence data (e.g. climate envelope models), we argue that this warrants further study and caution in their use. To aid other ecologists in making use of the methods described, code to implement them in freely available software is provided in an electronic appendix.
Pollinators are a key component of global biodiversity, providing vital ecosystem services to crops and wild plants. There is clear evidence of recent declines in both wild and domesticated pollinators, and parallel declines in the plants that rely upon them. Here we describe the nature and extent of reported declines, and review the potential drivers of pollinator loss, including habitat loss and fragmentation, agrochemicals, pathogens, alien species, climate change and the interactions between them. Pollinator declines can result in loss of pollination services which have important negative ecological and economic impacts that could significantly affect the maintenance of wild plant diversity, wider ecosystem stability, crop production, food security and human welfare.
Factors that determine the relative abundance of bumblebee species remain poorly understood, rendering management of rare and declining species difficult. Studies of bumblebee communities in the Americas suggest that there are strong competitive interactions between species with similar length tongues, and that this competition determines the relative abundance of species. In contrast, in Europe it is common to observe several short-tongued species coexisting with little or no evidence for competition shaping community structure. In this study we examine patterns of abundance and distribution in one of the most diverse bumblebee communities in Europe, found in the mountains of southern Poland. We quantify forage use when collecting nectar and pollen for 23 bumblebee species, and examine patterns of co-occurrence and niche overlap to determine whether there is evidence for inter-specific competition. We also test whether rarity can be explained by diet breadth. Up to 16 species were found coexisting within single sites, with species richness peaking in mountain pasture at ~1000m altitude. Results concur with previous studies indicating that the majority of pollen collected by bumblebees is from Fabaceae, but that some bee species (e.g. B. ruderatus) are much more heavily dependent on Fabaceae than others (e.g. B. lucorum). Those species that forage primarily on Fabaceae tended to have long tongues. In common with studies in the UK, diet breadth was correlated with abundance: rarer species tended to visit fewer flower species, after correcting for differences in sample size. No evidence was found for similarity in tongue length or dietary overlap influencing the likelihood of co-occurrence of species. However, the most abundant species (which co-occurred at most sites) occupied distinct dietary niche space. While species with tongues of similar length tended, overall, to have higher dietary niche overlap, among the group of abundant short-tongued species that commonly co-occurred there was marked dietary differentiation which may explain their coexistence.
As urbanisation increases globally and the natural environment becomes increasingly fragmented, the importance of urban green spaces for biodiversity conservation grows. In many countries, private gardens are a major component of urban green space and can provide considerable biodiversity benefits. Gardens and adjacent habitats form interconnected networks and a landscape ecology framework is necessary to understand the relationship between the spatial configuration of garden patches and their constituent biodiversity. A scale-dependent tension is apparent in garden management, whereby the individual garden is much smaller than the unit of management needed to retain viable populations. To overcome this, here we suggest mechanisms for encouraging 'wildlife-friendly' management of collections of gardens across scales from the neighbourhood to the city.
Pollinators may be declining globally, a matter of concern because animal pollination is required by most of the world's plant species, including many crop plants. Human land use and the loss of native habitats is thought to be an important driver of decline for wild, native pollinators, yet the findings of published studies on this topic have never been quantitatively synthesized. Here we use meta-analysis to synthesize the literature on how bees, the most important group of pollinators, are affected by human disturbances such as habitat loss, grazing, logging, and agriculture. We obtained 130 effect sizes from 54 published studies recording bee abundance and/or species richness as a function of human disturbance. Both bee abundance and species richness were significantly, negatively affected by disturbance. However, the magnitude of the effects was not large. Furthermore, the only disturbance type showing a significant negative effect, habitat loss and fragmentation, was statistically significant only in systems where very little natural habitat remains. Therefore, it would be premature to draw conclusions about habitat loss having caused global pollinator decline without first assessing the extent to which the existing studies represent the status of global ecosystems. Future pollinator declines seem likely given forecasts of increasing land-use change.
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Phenology and flower preferences of wild bees on the campus of Ibaraki University, Mito, Central Japan
- N Saito
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- Saito N.
Species composition of wild bees and their flower utilization in coastal sand dune vegetation at Ajigaura Beach, Ibaraki, central Japan
- M Hisamatsu
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