Dokument: Behavioural and ecological dynamics in competitive pollination networks
| Titel: | Behavioural and ecological dynamics in competitive pollination networks | |||||||
| URL für Lesezeichen: | https://docserv.uni-duesseldorf.de/servlets/DocumentServlet?id=34439 | |||||||
| URN (NBN): | urn:nbn:de:hbz:061-20150602-090541-6 | |||||||
| Kollektion: | Dissertationen | |||||||
| Sprache: | Englisch | |||||||
| Dokumententyp: | Wissenschaftliche Abschlussarbeiten » Dissertation | |||||||
| Medientyp: | Text | |||||||
| Autor: | Papiorek, Sarah [Autor] | |||||||
| Dateien: |
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| Dewey Dezimal-Klassifikation: | 500 Naturwissenschaften und Mathematik » 570 Biowissenschaften; Biologie | |||||||
| Beschreibung: | Flowers interact with several flower-visitors that remarkably differ, among others, in their morphologies, foraging strategies, and nutritional requirements, and thus in their efficiency to act as pollinators. In order to forage as effective as possible, flower-visitors rely on specific floral traits to detect and handle flowers in the heterogeneous environment they inhabit. Classical pollination syndromes comprise the identity and combination of specific floral traits, e.g. long corolla tubes or sweet scent. These flower traits are traditionally assumed to bear an adaptive value in relation to those flower-visitors that act as pollinators. However, the network between flowers and flower-visitors includes mutualistic as well as antagonistic relationships. Hence, floral traits may have not solely evolved to attract pollinators, but rather evolved to diminish antagonistic relationships with non-pollinating flower-visitors, and thus structure competitive pollination networks. Due to striking differences in colour vision systems, neural processing, and colour choice behaviours across flower-visitor taxa, floral colouration may have developed private communication channels between flowers and selective flower-visitors.
Focusing on bees and birds as flower-visitors and on bee- and bird-pollinated flowers, the present study reveals that floral colouration partially acts as such a floral filter structuring pollination networks. Choice experiments show that specific colour parameters selectively attract bees. Thereby bees prefer colours of high bee-subjective spectral purity, whereas flower-visiting birds do not show any preferences for colours or specific colour parameters. Consequently, the colour choice behaviour of flower-visitors affects the colouration of flowers pollinated by them. The comparison of flower colours reveals marked differences between those flowers pollinated by either bees or birds. We found that the floral colouration is well adapted to the visual capabilities of pollinators, but, at times, in addition negatively affects the visitation frequency of antagonistically operating visitors due to comparably less attractive colours. This is true for red and white flowers, which differ in their spectral reflectance depending on the pollinator guild, i.e. bees or birds. We show that the main differences in spectral reflectance arise in ultraviolet (UV)-reflectance properties. Here, the amount of UV-light determines bee-subjective spectral purity, making red and white bee-pollinated flowers more attractive for bees than red and white bird-pollinated ones, respectively. Red and white colours of bird-pollinated flowers display such a low spectral purity and low colour contrast to the background that the flowers are difficult to detect for the bees’ eye. Hence, the red and white colouration of bird-pollinated flowers acts as a sensorial floral filter, almost exclusively attracting the beneficial visitors. The attractive function for birds has not arisen from colour-preferences per se, but has rather result from learning in birds that associate these colours with higher amounts of nectar rewards, which are not depleted by bees. In contrast, for yellow flowers we show that the main colour does not differ between those pollinated exclusively by either bees or birds, and that yellow bird-pollinated flowers do not create a private niche for birds via a colour-based communication channel. However, we show that intra-floral colour patterns exclusively appear in yellow bee-, but not in yellow bird-pollinated flowers. Nonetheless, bees are known to prefer colour patterns as they guide them to the site of reward and thus, enhance their foraging efficiency due to decreased handling time. Hence, we conclude that yellow bee-pollinated flowers and their pollinators are well adapted to each other and that yellow bird-pollinated flowers hamper bees as antagonistically operating non-pollinating visitors from effective foraging. Furthermore, the present study investigates the impact of pigment chemistry and cell morphology on floral colouration. We show that an increase of pigment concentration causes a parallel increase of the bees' subjective spectral purity. However, this is true only up to intermediate concentrations, with even higher concentrations the spectral purity decreases. In accordance, choice experiments show that bees prefer colours of intermediate rather than of low or high pigment concentration. In addition, the flowers’ epidermal cell structure may affect floral colouration and structure the network of flowers, their mutual pollinators and antagonists. We show that bee-pollinated flowers on average possess more often conical epidermal cells, whereas bird-pollinated ones possess flat epidermal cells. Conical epidermal cells are assumed to act as light traps, enhancing the strength of the flowers’ colour signal. However, we show that the ambiguity of epidermal cell shape depends on the main pollinator as well as on the flower part, but does not affect the petals’ colouration as predicted. Nevertheless, epidermal cell shape affects mechanical properties in respect of floral grip, which influence the handling by bees that land on flowers, but not that by hovering birds. It is known that the possession of conical epidermal cells facilitates the bees’ grip, whereas flat epidermal cells cause a slippery surface. As grip is furthermore important for nectar robbing bees, the possession of flat epidermal cells on those flower parts that are vulnerable to nectar robbing is assumed to represent a mechanical floral filter. In fact, this is the case for bee- as well as bird-pollinated flowers. | |||||||
| Lizenz: |  Urheberrechtsschutz | |||||||
| Fachbereich / Einrichtung: | Mathematisch- Naturwissenschaftliche Fakultät » WE Biologie | |||||||
| Dokument erstellt am: | 02.06.2015 | |||||||
| Dateien geändert am: | 02.06.2015 | |||||||
| Promotionsantrag am: | 15.12.2014 | |||||||
| Datum der Promotion: | 02.02.2015 |
