Factors contributing to the natural reproductive performance of flowers, plants and populations of British and Mediterranean Orchidaceae are considered. Reproductive success is found to be pollinator limited, with most European orchids failing to achieve their maximum potential within the season, particularly nectarless species. There is a consistent discrepancy in gender function, with many more pollinia being removed than returned, because of pollinator foraging behaviour. Patterns of insect visitation to orchids are influenced by inflorescence and labellum characters, such as floral spurs. Spurs vary in size and shape between species, and many are nectarless. Trichomes are often present on the inner surface, and may prolong insect visits. The principal orchid pollinators are all members of the Hymenoptera, Lepioptera and Diptera, which normally visit other plants for food. Co-occurring species can act in a facilitative way to maintain a band of local pollinator, and pollination of all species examined is found to be significantly associated with the presence of 1 or 2 key foreign species or a guild of such plants. Under conditions of infrequent pollination, various features of the European Orchidaceae act to maximise their reproductive success when pollination does occur. The flowers are found to be long-lived and remain receptive to additional pollinations which may lead to increased seed quantity and diversity. Pollen maintains viability for several week which prolongs the opportunity of insect transported pollinia to effect pollination. Break up of pollinia into smaller dispersal units increases the likelihood of widespread dispersal and reduces pollen wastage. Even the smallest pollen load is found to stimulate embryogenesis, but more seeds are set with larger loads. PL:O ratios of 2-3:1 are most commonly found, which should result in both maximal seed set and increased quality of the offspring. Furthermore, seed output is significantly associated with fruit set and average levels of capsule formation are consistently higher in nectariferous orchids than in nectarless ones. Most rare British orchids are nectarless, and are particularly vulnerable to environmental alterations which influence the floral composition of their habitat, and density and distribution of supporting species.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:593211 |
| Date | January 1994 |
| Creators | Neiland, Mary Ruth Miller |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU072992 |
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