Browsing by Subject "Pollinators"

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Zierpflanzen als Nahrungsquelle und Bewertung der Blütenmerkmale für die Attraktivität der Bestäuberinsekten im urbanen Raum
(2022) Marquardt, Melanie; Rosenkranz, Peter
Currently, an increasing extension of urban areas can be observed worldwide, which implies a concurrent loss in natural habitats. If the current biodiversity shall be preserved, efforts must be reinforced in order to provide alternative habitats for the flora and fauna in urban areas. Regarding the assessment of the ecological value of the habitat ‘city’, scientific studies came to varying conclusions. However, all of them emphasize the importance of green urban areas in promoting the urban biodiversity. It has been frequently pointed out that sufficient and suitable foraging resources are an important and basic requirement for the survival of flower-visiting insects. However, it has hardly been investigated whether ornamental plants are suitable foraging resources for insect pollinators. While this is still highly contentious, there is growing evidence that ornamental plants could contribute to the provision of pollen and nectar. But apparently, the attractivity of different ornamental plants varies widely and furthermore, not all pollinator groups can profit equally from the mostly exotic ornamental plants. At present, scientific data for all ornamental genera or even species are not available. So, the first aim of this study was the comparison of the attractivity of certain ornamental plants, in particular those with a high market value. In order to conduct such trials, already existing acquisition methods have been assessed and refined. A further and so far rarely considered focus of this thesis is the analysis of impact factors that might affect the composition and abundance of urban pollinators. In order to identify the pollinator friendliness of ornamental plants, field tests in urban areas and semi-field tests in flight tents were conducted during the years 2017 – 2019. In the first trail, raised flower beds with an identical set of ornamental plants were installed at 13 different locations in the city area of Stuttgart. During the summer months of the years 2017 and 2018, all flower beds were visited in weekly intervals. Over a time period of 20 minutes, the number of foraging insects – divided into different groups of insect pollinators – was recorded. In total, 10,565 nectar and/or pollen foraging insects were counted. First of all, this confirms that our selection of ornamental plants was used as a foraging resource by pollinating insects. The attractivity of the tested ornamental plants, however, varied to a considerable degree among the plant species and the number of counts ranged from 1.2 flower visits in 20 minutes on Bracteantha bracteata (strawflower) to 5.3 flower visits on Bidens (beggar-ticks). It is noteworthy, that the attractivity also varied within the cultivars of the same species, partly even to a greater extent than between species. Interestingly, not only the abundance but also the composition of pollinators varied among the different test plants. Furthermore, the applied statistical models indicate significant impacts of the study year and the location on the results. This highlights the need of a continuously testing of all ornamental plants in regard to insect friendliness, for which the described methods were found to be very appropriate (publication I). Pollinating insects often use characteristic floral traits of the plants for their decision to visit the respective flower. These floral traits are often genera-, species- or even cultivar-specific and have been well studied in the native plants. In contrast, very little is known about the role of floral traits in ornamental plants. This includes e. g. the petal colour, several floral morphomet-rics or the floral scent of different plants. The impact of these traits on attractivity for insects was analysed in semi-field experiments using Calibrachoa cultivars and Bombus terrestris as model pollinator. Similar to the first part of the thesis, the attractivity of the different cultivars varied significantly. While the floral scent explained the observed differences in attractivity only to a small extend, it could be shown unequivocally that the petal colour constitutes a significant factor in the attractivity on B. terrestris. For a better understanding on the impact of certain floral traits for pollinating insects, however, there is further research required (publication II).