Digital Theses Archive


Tesi etd-07192017-182729

Type of thesis
Semi-natural habitat typology affects wild bee community diversity in a sunflower-based agroecosystem
Scientific disciplinary sector
relatore Dott.ssa MOONEN, ANNA CAMILLA
  • Agroecology
  • Agroecosystem
  • Apoidea
  • Semi-natural habitats
  • Wild bees
Exam session start date
General context - Agroecology aims to understand the ecology and functioning of species in a farming systems,as well as the mechanisms that govern their functioning and interactions among them. Semi-natural habitats (SNHs) are part of the agroecosystem and were recently introduced in the EU’s Common Agricultural Policy (CAP) since 2014, under the wider groups of Ecological Focus Areas. Farmers needs to be informed about the ecosystem services rovided by SNHs to crops, and their management and balance in the landscape. The correct management of SNHs will benefit biodiversity in agroecosystems, interrupting the constant decline registered in the recent past. Among beneficial insects, wild bees (Hymenoptera: Apoidea: Apiformes) provide pollination service to crops while, nowadays, the amount of insect pollinated crops worldwide is growing. At the same time many stressors for the wild bee populations are present in agroecosystems, such as lack of flower resources, use of agrochemicals, spread of pathogens, and simplification of agricultural landscapes. Those stressor are the cause of the reduction of many wild bees and honey bees populations registered worldwide.<br>Aim of the research - In order to better understand agroecological processes and contribute knowledge that can be useful for the design and management of sustainable agroecosystems, the present thesis investigates the role of SNHs to sustain wild bee diversity, and how wild bee spill-over (if do) from SNHs to sunflower influenced sunflower pollination in the Pisa plain. More specifically this PhD thesis explores: (i) the relation between SNHs typology and the wild bees community at local and landscape scale (Chapter 2); (ii) floral resources amount, diversity, and stability in the SNHs and how wild bees use these resources, analysed through network analysis (Chapter 3); (iii) the relation between pollinator visits and the yield of modern commercial sunflower varieties for oil production (Chapter 4); (iv) the actual pollinators of sunflower in the Pisa plain and how they relate with local and landscape factors (Chapter 5).<br>Results - Chapter 2 demonstrates that SNH types had different wild bee communities. Vegetation structure of woody elements favoured the turnover of wild bee species, enhancing diversity especially in woody linear habitats where also ecotone effect favoured wild bees. On the other hand, herbaceous elements had a higher average richness because flowering resources steadily attracted wild bees, but low turnover in space and time guaranteed less diversity. At landscape scale, a high amount of herbaceous linear SNHs favoured wild bee richness in June and July, while, in June a greater amount of herbaceous areal diminished wild bee richness, as well as the amount of woody areal and the total surface of semi-natural habitats in July.<br>Chapter 3 reveals that herbaceous elements had a higher stability of flower resources and robustness of plant-wild bees networks, but at the same time woody elements host peculiar, abundant resources which seem to be crucial for the community of wild bees and are keystones for the networks. At the landscape scale the role of the amount of herbaceous linear elements in the landscape in sustaining both wild bees and flowering plants was very important, favouring robustness of the network.<br>Chapter 4 provides evidence that sunflower yields are greatly dependent on cross-pollination events and those events are exclusively driven by sunflower visitors, which were mainly honey bee. There was no clear evidence of pollination deficits lessening crop productivity.<br>Chapter 5 demonstrates that in the Pisa plain the principal wild bee genus visiting sunflower was Bombus, however 28 wild bee morphospecies were also found. Bumble bee richness and abundance were negatively related to minimum tillage of the field, probably affected by the high amount of herbicides used in minimum tillage systems. Bumble bees were also positively related to the percentage of urban areas in the surrounding landscape.<br>Discussion and future perspectives - In conclusion, from the various approaches applied in this study aimed at elucidating spatial and temporal patterns of wild bees in a sunflower-based agroecosystem in the Mediterranean region, we can conclude that although pollination in sunflower seems to be guaranteed by honey bees, wild bees do rely on unflower, and at a landscape scale, the diversity of floral resources offered by semi-natural habitats provide the basis for several mutualistic wild bee networks in space and in time. Thus all the SNHs types are worthy of protection and need specific management programmes involving the entire agroecosystem, including all local and land managers such as farmers, public land managers, beekeepers and the general public.