Flowering native weeds for the conservation of wild pollinators in agroecosystems
- Autores: Jane Morrison
- Directores de la Tesis: Jordi Izquierdo (dir. tes.), José Luis González Andújar (codir. tes.)
- Lectura: En la Universitat Politècnica de Catalunya (UPC) ( España ) en 2018
- Idioma: español
- Tribunal Calificador de la Tesis: Francisco Javier Sans Serra (presid.), Jordi Comas Angelet (secret.), Alicia Cirujeda Ranzenberger (voc.)
- Programa de doctorado: Programa de Doctorado en Tecnología Agroalimentaria y Biotecnología por la Universidad Politécnica de Catalunya
- Materias:
- Enlaces
- Tesis en acceso abierto en: TDX
- Resumen
Concerns about a global decline in pollinators have called for more knowledge about the drivers of wild pollinator abundance and diversity in agroecosystems. Agricultural intensification has been identified as the main cause of this “global pollinator crisis”, particularly, due to reductions in natural areas holding critical floral and nesting resources. Maintaining flowering weeds in agricultural field margins is often recommended as a cost-effective and efficient method of offering natural or semi-natural habitats for wild pollinator conservation.
In this study, the role of flowering weeds in supporting wild bees and other flower visiting insects in Mediterranean cereal agroecosystems was investigated. This research involved a three-year, multi-farm study (Part A) which compared field margin characteristics, including the functional constitution of their floral communities, with wild bee community composition and functional structure, from sites with landscapes of varying agricultural intensity in Catalonia, Spain. The aim of this work was to investigate the value of field margins in differing landscapes and determine which biotic and abiotic margin characteristics, and which functional attributes of margin plant communities, were important for sustaining wild bee abundance and diversity. This work also involved a two-year field trial (Part B) to compare five native flowering weed species common in Catalan cereal agroecosystems: C. arvensis, D. carota, M. sylvestris, P. rhoeas and S oleraceus. The goal was to compare the attractiveness of these species to different flower visiting insect groups, assess their value in supporting wild pollinators and analyze relationships between particular floral characteristics and insect visitation rates.
Overall, more than 4000 bees were collected and identified to genus and a database was compiled listing the morphophysiological features and behaviours of the observed genera. A large database was also compiled of all the flowering plant species observed in Part A, documenting the trait values relevant for this work. In Part A, generalized linear models indicated a strong inverse relationship between surrounding landscape diversity and wild bee abundance. The proportion of Halictidae bees (common generalists) increased with decreasing landscape complexity. Floral richness exhibited a positive association with number of foraging bees and morphospecies richness, and was positively correlated with the proportion of shrubs and trees represented in the margins. It was observed that wider margins held a higher proportion of perennial plants and a lower proportion of Halictidae bees. The functional attributes of margin plant communities that were observed to promote wild bee community robustness included: high nectar availability, diversity in flower colour, diversity in flower morphology and diversity in vegetation height. In Part B, the most visited species were P. rhoeas and D. carota (more visits to P. rhoeas in 2015 and more visits to D. carota in 2016), followed by mixed plots, M. sylvestris, C. arvensis and S. oleraceus. The influence of the specific floral traits of the studied species on visitation rates, calculated using general linear models, varied depending on the insect group. This study suggests that field margins are more crucial in intensively farmed areas than in heterogeneous landscapes where foraging resources are more abundant. Maintaining wide margins with high flowering plant richness, comprising perennial and shrub species, best supports a dense and diverse bee community. If necessary, it is recommended that margins be sown with native perennial flowers, with differing and overlapping flowering periods, high in nectar and pollen, with a diverse assortment of colours, shapes and plant heights, and that they be managed so that a diversity of nesting features are offered.
