1,721,029 research outputs found
Contrasting effects of past and present mass-flowering crop cultivation on bee pollinators shaping yield components in oilseed rape
No full textThe cultivation of mass-flowering crops (MFC) can promote pollinators by providing floral resources. However, there is missing knowledge about the effect of MFC cultivation history on bees and their pollination services in agricultural landscapes. We investigated how bee densities in oilseed rape (Brassica napus L.) (OSR) fields were affected by past (cultivation area of the preceding three years) and current MFC area coverages in the surrounding landscape. Moreover, we analyzed how insect pollination, its possible interaction with the plants` pod numbers and MFC covers influence yield components of individual OSR plants and calculated yields (t/ha). To test this, we conducted pollinator surveys and a pollinator exclusion experiment in one oilseed rape field in 17 agricultural landscapes in Germany. We found that wild bee densities were positively affected by past MFC covers and negatively impacted by current OSR covers, indicating enhanced pollinator populations due to previous MFC cultivation and contemporary pollinator dilution. In contrast, honeybees showed opposite responses to past and present MFC cultivation. Furthermore, seed weight per plant of open pollinated plants was positively correlated with past MFC covers. Pollinator exclusion decreased the seed number per pod and increased thousand-seed weight, while yields were unaffected. Pod number interacted with insect pollination in shaping yields, such that pollinator exclusion led to a steeper increase of yield with higher pod numbers. Insect pollination compensated for low pod numbers by increasing the plants` seed number per pod and ultimately yields. Our findings demonstrate a beneficial effect of high MFC covers in the past on bee densities and potentially yield components in the current year. Our study highlights the need for further research on how past and present landscape composition in terms of MFC cultivation interactively affect pollinator communities and their pollination services in agricultural landscapes
Landscape composition modifies pollinator densities, foraging behavior and yield formation in faba beans
No full textWildlife-friendly management practices promote pollinators and pollination services in agricultural landscapes. Wild bee densities are driven by landscape composition, as they benefit from an increased availability of nesting and foraging resources at landscape scale. However, effects of landscape composition on bee foraging decisions and consequences for crop pollination have rarely been studied. We investigated, how landscape composition affects bee densities and foraging behavior in faba bean (Vicia faba L.) fields and how this impacts faba bean yield. We recorded densities and nectar robbing behavior of honeybees, long- tongued and short-tongued bumblebees in faba bean fields in eleven landscapes with varying landscape composition (e.g. land cover of oilseed rape, faba bean and semi-natural habitats). Moreover, we assessed yield components of faba beans via pollinator exclusion experiments. Increasing covers of faba bean and semi-natural habitats positively influenced bumblebee densities, while high oilseed rape covers negatively affected short-tongued bumblebee densities in bean fields. Increased faba bean covers enhanced the proportion of nectar-robbing short-tongued bumblebees. The number of beans per pod was increased by insect pollination, while the number of pods was decreased; these effects however depended on variety. Landscape composition interacted with bee densities in shaping yield components in V. faba. Our study emphasizes the importance of considering landscape management to maximize crop yields, as shown for the case of faba beans. The composition of agricultural landscape can modulate bee densities in crop fields, bees` foraging behavior and pollination services
Beta diversity at different spatial scales: Plant communities in organic and conventional agriculture
No full textBiodiversity studies that guide agricultural subsidy policy have generally compared farming systems at a single spatial scale: the field. However, diversity patterns vary across spatial scales. Here, we examined the effects of farming system (organic vs. conventional) and position in the field (edge vs. center) on plant species richness in wheat fields at three spatial scales. We quantified alpha-, beta-, and gamma-diversity at the microscale in 800 plots, at the mesoscale in 40 fields, and at the macroscale in three regions using the additive partitioning approach, and evaluated the relative contribution of beta-diversity at each spatial scale to total observed species richness. We found that alpha-, beta-, and gamma-diversity were higher in organic than conventional fields and higher at the field edge than in the field center at all spatial scales. In both farming systems, beta-diversity at the meso- and macroscale explained most of the overall species richness (up to 37% and 25%, respectively), indicating considerable differences in community composition among fields and regions due to environmental heterogeneity. The spatial scale at which beta-diversity contributed the most to overall species richness differed between rare and common species. Total richness of rare species (present in 25% of total samples) was explained by differences in community composition at the micro- and mesoscale (up to 29% and 47%, respectively), i.e., among plots and fields, independent offarming system. Our results show that organic farming made the greatest contribution to total species richness at the meso (among fields) and macro (among regions) scale due to environmental heterogeneity. Hence, agri-environment schemes should exploit this large-scale contribution of beta-diversity by tailoring schemes at regional scales to maximize dissimilarity between conservation areas using geographic information systems rather than focusing entirely at the classical local-field scale, which is the current practice
The effects of landscape complexity on arable weed species diversity in organic and conventional farming
No full text1.There is growing concern about declining species diversity in agro-ecosystemscaused by agricultural intensification at the field and landscape scales. Species diversityof arable weeds is classically related to local abiotic factors and resource conditions. Itis believed to be enhanced by organic farming but the surrounding landscape may alsobe important. 2. This study assessed the ruderal vegetation, seed bank and seed rain in 24 winterwheat fields to examine the relative importance of organic vs. conventional farming andlandscape complexity for weed species diversity. Diversity was partitioned into itsadditive components: alpha, beta and gamma diversity. Percentage arable land in acircular landscape sector of 1-km radius around each study site was used as an indicatorof landscape complexity. 3. Weed species diversity in the vegetation, seed rain and seed bank was higher inorganic than in conventional fields. Increasing landscape complexity enhanced speciesdiversity more strongly in the vegetation of conventional than organic fields, to the extentthat diversity was similar in both farming systems when the landscape was complex.Species diversity of the seed bank was increased by landscape complexity irrespective offarming system. 4. Overall diversity was largely determined by the high heterogeneity between andwithin the fields (beta diversity). Only in very few cases could higher weed species diversityin complex landscapes and/or organic farming be related to species dependence onlandscape or farming system. 5. Synthesis and applications. Local weed species diversity was influenced by bothlandscape complexity and farming system. Species diversity under organic farmingsystems was clearly higher in simple landscapes. Conventional vegetation reached similardiversity levels when the surrounding landscape was complex through the presence ofrefugia for weed populations. Consequently, agri-environment schemes designed topreserve and enhance biodiversity should not only consider the management of singlefields but also of the surrounding landscape
Crop pollination services: Complementary resource use by social vs solitary bees facing crops with contrasting flower supply
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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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