Abstract
The PhD thesis has studied the pollination ecology of two popular fruit trees used in agro-forestry parklands in The Gambia and Burkina Faso. Both species are economically and nutritionally important.
The methods used have been a combination of size-based exclusion trials and direct observations of the potential pollinators in the flowers. For one of the species, a number of seeds from the resulting pods were genotyped and the distances to the assigned father trees were found. Due to relatively few flower-visitors it was possible to assign the effective pollinators for both species.
The main results for Vitellaria paradoxa subsp. paradoxa are the findings that honey bees were the most efficient pollinators, and that stingless bees and solitary bees partly could compensate honey bees. The stingless bees often construct nests in older V. paradoxa trees, and when excluding honey bees, these trees yielded significantly more than trees without nests. Furthermore, a relationship between fertilisation percentages and number of honey bee colonies within radii of 900 m and 1,000 m was found.
Parkia biglobosa is known to be pollinated by bats, and the study in The Gambia showed that honey bees were also effective pollinators. Furthermore, in absence of bats and honey bees, stingless bees were found to be able to partly compensate honey bees, but the pods had more aborted seeds. In Burkina Faso, two climatically different study sites were used for studying the potential impact of climate changes on the pollination ecology of P. biglobosa. In the drier site, the tree density was lower and only few bats were present. Honey bees were found to be the main pollinators, and the pollination by small bees (stingless and solitary bees) resulted in very few pods. In the more humid site, tree density was higher and many bats were present. Still, the treatment excluding bats gave statistically the same yield, except that the mean pollen flow distance was larger for the open-pollinated flowers. The treatment allowing access to only small bees resulted in few pods but significantly more than at the drier site. Other differences between sites were the higher rate of abortion, higher percentage of selfing, fewer pollen donors, and larger median pollen flow distances found at the drier site.
The methods used have been a combination of size-based exclusion trials and direct observations of the potential pollinators in the flowers. For one of the species, a number of seeds from the resulting pods were genotyped and the distances to the assigned father trees were found. Due to relatively few flower-visitors it was possible to assign the effective pollinators for both species.
The main results for Vitellaria paradoxa subsp. paradoxa are the findings that honey bees were the most efficient pollinators, and that stingless bees and solitary bees partly could compensate honey bees. The stingless bees often construct nests in older V. paradoxa trees, and when excluding honey bees, these trees yielded significantly more than trees without nests. Furthermore, a relationship between fertilisation percentages and number of honey bee colonies within radii of 900 m and 1,000 m was found.
Parkia biglobosa is known to be pollinated by bats, and the study in The Gambia showed that honey bees were also effective pollinators. Furthermore, in absence of bats and honey bees, stingless bees were found to be able to partly compensate honey bees, but the pods had more aborted seeds. In Burkina Faso, two climatically different study sites were used for studying the potential impact of climate changes on the pollination ecology of P. biglobosa. In the drier site, the tree density was lower and only few bats were present. Honey bees were found to be the main pollinators, and the pollination by small bees (stingless and solitary bees) resulted in very few pods. In the more humid site, tree density was higher and many bats were present. Still, the treatment excluding bats gave statistically the same yield, except that the mean pollen flow distance was larger for the open-pollinated flowers. The treatment allowing access to only small bees resulted in few pods but significantly more than at the drier site. Other differences between sites were the higher rate of abortion, higher percentage of selfing, fewer pollen donors, and larger median pollen flow distances found at the drier site.
| Original language | English |
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| Publisher | Department of Geosciences and Natural Resource Management, Faculty of Science, University of Copenhagen |
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| Number of pages | 140 |
| Publication status | Published - 2016 |